Tek 2235A re-cap


vdonisa
 

Hi All,

I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)

The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.

What I noticed:

- there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)

- C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)

- all other caps were looking OK

For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.

Now for the questions:

- does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)

- there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?

- looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?

- any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?

- anything else that you gentlemen know to be frequently failing and should be replaced?

Thanks!


 

On Sat, 30 Mar 2013 15:57:23 -0000, "vdonisa" <vdonisa@yahoo.com>
wrote:

Hi All,

I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)

The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.

What I noticed:

- there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)

- C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)

- all other caps were looking OK

For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.

Now for the questions:

- does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)
They look like fine choices to me. I like the comparable Nichicon PW
series myself. One of that advantages of the saturable core inverter
design that Tektronix liked to use is its lower ripple current
compared to pulse width modulator based designs.

- there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?
The small distributed bulk decoupling capacitors can still wear out
with age. If you have an impedance bridge or similar, you could test
a couple of the easier to reach ones to see what condition they are
in. If they are marginal, then I would change them all.

- looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?
I do not think there is any reason to over specify them. They
probably wore out do to temperature and age. I thought there might
have been a service bulletin where they were changed but did not find
anything.

- any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?
I do not. I just make modifications to I can use a good radial or
snap in replacement.


vdonisa
 

Hi David,

And thanks for your reply.

Just wanted to let you know that Kemet is still doing those 4-pin capacitors, however nobody has in stock the particular 270u/450V value. The closest available is 330u/450V, available at mouser, Kemet part number is ALC10C331ED450, however it has 40mm diameter (instead of 35mm the original United Chemi), I was afraid that it won't fit (the EMI filter cover is too close) so I didn't order one. According to Kemet's catalog they also manufacture some 270u and 330u with 35mm diameter however I wasn't able to find any stock. The key to searching is to look for "ALC10C" the last letter (C) indicates 4 pin construction. The ALC10A's are 2 pin.

If anyone finds them in stock somewhere please kindly let us know :-)

I was partial to Panasonic since I was able to find in stock nearly the whole set of values I needed - it just looks neat to have all the caps in same color and top vent shape :-) Otherwise I think they key is to check the specs and buy from authorized dealers only, I wouldn't trust any cap from e-bay or alibaba :-)

I'll check those 22uF on the daughter boards too. I was just wondering - those that are used just for local power decoupling, could they be replaced with 10uF ceramics? (this is the largest size of ceramics available to me at decent price). Given the lowest ESR and better frequency response, they might work as well?

Otherwise, what's the group's experience with aluminum organic polymer ones, from a reliability POV? (I mean small caps like the 22u mentioned above).

Given the amount of work to disassemble / reassemble the daughter boards / shields etc I'd rather use something reliable from the beginning so I wouldn't need to revisit them later :-)

Thanks again!!!

--- In TekScopes@yahoogroups.com, David <davidwhess@...> wrote:

On Sat, 30 Mar 2013 15:57:23 -0000, "vdonisa" <vdonisa@...>
wrote:

Hi All,

I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)

The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.

What I noticed:

- there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)

- C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)

- all other caps were looking OK

For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.

Now for the questions:

- does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)
They look like fine choices to me. I like the comparable Nichicon PW
series myself. One of that advantages of the saturable core inverter
design that Tektronix liked to use is its lower ripple current
compared to pulse width modulator based designs.

- there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?
The small distributed bulk decoupling capacitors can still wear out
with age. If you have an impedance bridge or similar, you could test
a couple of the easier to reach ones to see what condition they are
in. If they are marginal, then I would change them all.

- looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?
I do not think there is any reason to over specify them. They
probably wore out do to temperature and age. I thought there might
have been a service bulletin where they were changed but did not find
anything.

- any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?
I do not. I just make modifications to I can use a good radial or
snap in replacement.


 

On Sat, 30 Mar 2013 17:45:30 -0000, "vdonisa" <vdonisa@yahoo.com>
wrote:

Hi David,

And thanks for your reply.

Just wanted to let you know that Kemet is still doing those 4-pin capacitors, however nobody has in stock the particular 270u/450V value. The closest available is 330u/450V, available at mouser, Kemet part number is ALC10C331ED450, however it has 40mm diameter (instead of 35mm the original United Chemi), I was afraid that it won't fit (the EMI filter cover is too close) so I didn't order one. According to Kemet's catalog they also manufacture some 270u and 330u with 35mm diameter however I wasn't able to find any stock. The key to searching is to look for "ALC10C" the last letter (C) indicates 4 pin construction. The ALC10A's are 2 pin.
I do not even bother looking for them any more. Either they are
difficult to find or they cost a lot more than a snap in or radial
capacitor. For the same reason I usually do not bother looking for
axial replacements either.

I was partial to Panasonic since I was able to find in stock nearly the whole set of values I needed - it just looks neat to have all the caps in same color and top vent shape :-) Otherwise I think they key is to check the specs and buy from authorized dealers only, I wouldn't trust any cap from e-bay or alibaba :-)
Besides being long life and low impedance, I like the PW series
because they have good availability, are inexpensive, and are
available with ratings up to 450 volts.

There are lots of other electrolytic capacitors which are just as good
though.

I'll check those 22uF on the daughter boards too. I was just wondering - those that are used just for local power decoupling, could they be replaced with 10uF ceramics? (this is the largest size of ceramics available to me at decent price). Given the lowest ESR and better frequency response, they might work as well?
The very low ESR of ceramic capacitors can sometimes cause problems
but I doubt that would happen in this case because the power trace
impedance would decouple them from the power supply and other
circuits. For the same reason though, I would not expect them to
improve the performance and high dielectric constant ceramic
capacitors tend to be very sensitive to temperature and voltage so
10uF units could easily end up being 2.2uF in practice.

If cost is not a problem, I think voltage derated solid tantalums with
a minimum value of 4.7uF (to replace a 22uF aluminum electrolytic)
would be better.

Otherwise, what's the group's experience with aluminum organic polymer ones, from a reliability POV? (I mean small caps like the 22u mentioned above).
They have a low ESR like ceramic capacitors without the disadvantages
of high voltage coefficient and temperature coefficient of capacitance
and they have very high ripple current ratings compared to aluminum
electrolytic capacitors.

In high ripple current applications they are great but as a general
replacement for aluminum electrolytics in other applications, I
suspect they will not last as long. Most of the ones I have seen are
rated from 1000 to 2000 hours while long life aluminum electrolytics
could be 4 times that in low ripple current applications.

I am unclear about the long life wearout mechanism for aluminum
organic polymer capacitors.

Given the amount of work to disassemble / reassemble the daughter boards / shields etc I'd rather use something reliable from the beginning so I wouldn't need to revisit them later :-)
I do the same thing. I often use larger packages if possible and/or
use more voltage derating for greater reliability.


Tom Jobe <tomjobe@...>
 

For whatever reason, the three capacitors in the right rear corner of the mainboard fail on the 22xx scopes with your kind of power supply (C925, C942, C943) but they are easy to change without removing anything. Also in the same corner of the mainboard the SCR Q935 often fails on 22xx scopes, but your 2235A probably has the upgraded MCR72-4 SCR just like this one has, so you may have no worries there. I was just looking inside of this 2235A power supply to see how it differs from an ordinary 2235 and it is all quite similar, but upgraded in several ways.
tom jobe...
 
 

----- Original Message -----
From: vdonisa
Sent: Saturday, March 30, 2013 8:57 AM
Subject: [TekScopes] Tek 2235A re-cap

 

Hi All,

I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)

The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.

What I noticed:

- there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)

- C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)

- all other caps were looking OK

For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.

Now for the questions:

- does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)

- there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?

- looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?

- any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?

- anything else that you gentlemen know to be frequently failing and should be replaced?

Thanks!


vdonisa
 

This is interesting, maybe the gentleman that replaced C942 & C943 with 4.7u/250V knew something, anyway his repair has lasted. In my case C925 was OK and looked like being the original one.

Maybe I should find some 10u/250v although by looking at the schematic I can't understand how they would get so much voltage. Unless there's some weird transient action there at power turn on/off.

Other than this it might be the heat in that compartment, I probably should pull out the infrared thermometer and check what's going on.

Thanks!

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@...> wrote:

For whatever reason, the three capacitors in the right rear corner of the mainboard fail on the 22xx scopes with your kind of power supply (C925, C942, C943) but they are easy to change without removing anything. Also in the same corner of the mainboard the SCR Q935 often fails on 22xx scopes, but your 2235A probably has the upgraded MCR72-4 SCR just like this one has, so you may have no worries there. I was just looking inside of this 2235A power supply to see how it differs from an ordinary 2235 and it is all quite similar, but upgraded in several ways.
tom jobe...


----- Original Message -----
From: vdonisa
To: TekScopes@yahoogroups.com
Sent: Saturday, March 30, 2013 8:57 AM
Subject: [TekScopes] Tek 2235A re-cap



Hi All,

I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)

The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.

What I noticed:

- there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)

- C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)

- all other caps were looking OK

For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.

Now for the questions:

- does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)

- there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?

- looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?

- any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?

- anything else that you gentlemen know to be frequently failing and should be replaced?

Thanks!


Tom Jobe <tomjobe@...>
 

Your observation that heat might be what kills those capacitors in the right rear corner of the mainboard, is probably worth considering.
The 2235A has a much improved aluminum heat sink for Q946, Q947 and Q9070 which might further aggravate the situation for those capacitors, while helping the transistors and the MOSFET attached to the heat sink.
Something you might consider is to use the onboard power supply for the 2236A case fan. The 2235A has the complete fan circuit less the capacitor C965. All of this is just in front of that aluminum heat sink, and the place for C965 is marked "2236A only". The back panel on the 2235A has a hole pattern to accept a standard 12 volt fan (50mm square bolt pattern on a 60mm diameter fan?), and the pins to connect the fan's power are just ahead of the heat sink and marked "W9965".
If you look at the power supply schematic for a 2232 or a 2236A you will see the fan circuit and component numbers. I may have a copy of the fan schematic around here somewhere, but I think there is a free copy of the 2232 manual in several places. You don't even need the schematic if you decide to do this mod, just connect the fan with the polarity that moves the air in whichever direction you prefer.
I have added this fan circuit to several 22xx scopes. Many of the older 22xx scopes had some kind of an undocumented fan circuit on the mainboard but you had to populate it. The 2215A and 2235 scopes would be examples that had the undocumented fan circuit.
tom jobe...
 
 
 

----- Original Message -----
From: vdonisa
Sent: Saturday, March 30, 2013 6:19 PM
Subject: [TekScopes] Re: Tek 2235A re-cap

 

This is interesting, maybe the gentleman that replaced C942 & C943 with 4.7u/250V knew something, anyway his repair has lasted. In my case C925 was OK and looked like being the original one.

Maybe I should find some 10u/250v although by looking at the schematic I can't understand how they would get so much voltage. Unless there's some weird transient action there at power turn on/off.

Other than this it might be the heat in that compartment, I probably should pull out the infrared thermometer and check what's going on.

Thanks!

--- In TekScopes@..., "Tom Jobe" wrote:
>
> For whatever reason, the three capacitors in the right rear corner of the mainboard fail on the 22xx scopes with your kind of power supply (C925, C942, C943) but they are easy to change without removing anything. Also in the same corner of the mainboard the SCR Q935 often fails on 22xx scopes, but your 2235A probably has the upgraded MCR72-4 SCR just like this one has, so you may have no worries there. I was just looking inside of this 2235A power supply to see how it differs from an ordinary 2235 and it is all quite similar, but upgraded in several ways.
> tom jobe...
>
>
> ----- Original Message -----
> From: vdonisa
> To: TekScopes@...
> Sent: Saturday, March 30, 2013 8:57 AM
> Subject: [TekScopes] Tek 2235A re-cap
>
>
>
> Hi All,
>
> I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)
>
> The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.
>
> What I noticed:
>
> - there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)
>
> - C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)
>
> - all other caps were looking OK
>
> For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.
>
> Now for the questions:
>
> - does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)
>
> - there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?
>
> - looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?
>
> - any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?
>
> - anything else that you gentlemen know to be frequently failing and should be replaced?
>
> Thanks!
>


vdonisa
 

Hi Tom,

Thanks for your answer!

I was thinking of a fan too (a low noise low RPM one that would just move the air a little bit without sounding like a vacuum cleaner like my HP 3325A lol). But then I was not sure where I could connect it without disturbing the power supply too much. Now that I know.... I do remember that connector, with an empty place for a capacitor nearby, I just didn't know what exactly it was for.

Otherwise if I can't find a decent fan solution, I already identified some 10u/100V that should be able to take some heat: Nichicon has them in their BT series (automotive 125 Celsius) also Rubycon in RX30 series.

Thanks again!

Valentin

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@...> wrote:

Your observation that heat might be what kills those capacitors in the right rear corner of the mainboard, is probably worth considering.
The 2235A has a much improved aluminum heat sink for Q946, Q947 and Q9070 which might further aggravate the situation for those capacitors, while helping the transistors and the MOSFET attached to the heat sink.
Something you might consider is to use the onboard power supply for the 2236A case fan. The 2235A has the complete fan circuit less the capacitor C965. All of this is just in front of that aluminum heat sink, and the place for C965 is marked "2236A only". The back panel on the 2235A has a hole pattern to accept a standard 12 volt fan (50mm square bolt pattern on a 60mm diameter fan?), and the pins to connect the fan's power are just ahead of the heat sink and marked "W9965".
If you look at the power supply schematic for a 2232 or a 2236A you will see the fan circuit and component numbers. I may have a copy of the fan schematic around here somewhere, but I think there is a free copy of the 2232 manual in several places. You don't even need the schematic if you decide to do this mod, just connect the fan with the polarity that moves the air in whichever direction you prefer.
I have added this fan circuit to several 22xx scopes. Many of the older 22xx scopes had some kind of an undocumented fan circuit on the mainboard but you had to populate it. The 2215A and 2235 scopes would be examples that had the undocumented fan circuit.
tom jobe...



----- Original Message -----
From: vdonisa
To: TekScopes@yahoogroups.com
Sent: Saturday, March 30, 2013 6:19 PM
Subject: [TekScopes] Re: Tek 2235A re-cap



This is interesting, maybe the gentleman that replaced C942 & C943 with 4.7u/250V knew something, anyway his repair has lasted. In my case C925 was OK and looked like being the original one.

Maybe I should find some 10u/250v although by looking at the schematic I can't understand how they would get so much voltage. Unless there's some weird transient action there at power turn on/off.

Other than this it might be the heat in that compartment, I probably should pull out the infrared thermometer and check what's going on.

Thanks!

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@> wrote:
>
> For whatever reason, the three capacitors in the right rear corner of the mainboard fail on the 22xx scopes with your kind of power supply (C925, C942, C943) but they are easy to change without removing anything. Also in the same corner of the mainboard the SCR Q935 often fails on 22xx scopes, but your 2235A probably has the upgraded MCR72-4 SCR just like this one has, so you may have no worries there. I was just looking inside of this 2235A power supply to see how it differs from an ordinary 2235 and it is all quite similar, but upgraded in several ways.
> tom jobe...
>
>
> ----- Original Message -----
> From: vdonisa
> To: TekScopes@yahoogroups.com
> Sent: Saturday, March 30, 2013 8:57 AM
> Subject: [TekScopes] Tek 2235A re-cap
>
>
>
> Hi All,
>
> I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)
>
> The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.
>
> What I noticed:
>
> - there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)
>
> - C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)
>
> - all other caps were looking OK
>
> For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.
>
> Now for the questions:
>
> - does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)
>
> - there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?
>
> - looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?
>
> - any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?
>
> - anything else that you gentlemen know to be frequently failing and should be replaced?
>
> Thanks!
>


Tom Jobe <tomjobe@...>
 

Hi Valentin,
Do yourself a favor and change those three capacitors in the right rear corner. If your scope has cooked C970 on the front side of the heat sink, things have been getting very hot in there.
I don't have a copy of the 2236A service manual so I ordered one today from Qservice in Greece. I would like to see what component values are specified for the 2236A fan supply.
This very nice 2235A I have had some ordinary problems in the power supply which I fixed a year or two ago. It had one remaining problem with channel 2 which had not been fixed. It turns out that U180 was dead in the vertical amplifier, so I replaced it with the similar part out of a 2235 (which has a different part number). The channel 2 voltage gain is now too low, so I removed the U180 that came from the 2235 and ordered the proper U180 part number for the 2235A.
It will be a week or two before the U180 part and the 2236A service manual arrive. I will let you know what I find out about this fan mod, etc.
tom jobe...
PS If anyone has a 2236A service manual, could I get you to look up the values of a few components in the electrical parts list?
 
 
 

----- Original Message -----
From: vdonisa
Sent: Monday, April 01, 2013 2:39 PM
Subject: [TekScopes] Re: Tek 2235A re-cap

 

Hi Tom,

Thanks for your answer!

I was thinking of a fan too (a low noise low RPM one that would just move the air a little bit without sounding like a vacuum cleaner like my HP 3325A lol). But then I was not sure where I could connect it without disturbing the power supply too much. Now that I know.... I do remember that connector, with an empty place for a capacitor nearby, I just didn't know what exactly it was for.

Otherwise if I can't find a decent fan solution, I already identified some 10u/100V that should be able to take some heat: Nichicon has them in their BT series (automotive 125 Celsius) also Rubycon in RX30 series.

Thanks again!

Valentin

--- In TekScopes@..., "Tom Jobe" wrote:
>
> Your observation that heat might be what kills those capacitors in the right rear corner of the mainboard, is probably worth considering.
> The 2235A has a much improved aluminum heat sink for Q946, Q947 and Q9070 which might further aggravate the situation for those capacitors, while helping the transistors and the MOSFET attached to the heat sink.
> Something you might consider is to use the onboard power supply for the 2236A case fan. The 2235A has the complete fan circuit less the capacitor C965. All of this is just in front of that aluminum heat sink, and the place for C965 is marked "2236A only". The back panel on the 2235A has a hole pattern to accept a standard 12 volt fan (50mm square bolt pattern on a 60mm diameter fan?), and the pins to connect the fan's power are just ahead of the heat sink and marked "W9965".
> If you look at the power supply schematic for a 2232 or a 2236A you will see the fan circuit and component numbers. I may have a copy of the fan schematic around here somewhere, but I think there is a free copy of the 2232 manual in several places. You don't even need the schematic if you decide to do this mod, just connect the fan with the polarity that moves the air in whichever direction you prefer.
> I have added this fan circuit to several 22xx scopes. Many of the older 22xx scopes had some kind of an undocumented fan circuit on the mainboard but you had to populate it. The 2215A and 2235 scopes would be examples that had the undocumented fan circuit.
> tom jobe...
>
>
>
> ----- Original Message -----
> From: vdonisa
> To: TekScopes@...
> Sent: Saturday, March 30, 2013 6:19 PM
> Subject: [TekScopes] Re: Tek 2235A re-cap
>
>
>
> This is interesting, maybe the gentleman that replaced C942 & C943 with 4.7u/250V knew something, anyway his repair has lasted. In my case C925 was OK and looked like being the original one.
>
> Maybe I should find some 10u/250v although by looking at the schematic I can't understand how they would get so much voltage. Unless there's some weird transient action there at power turn on/off.
>
> Other than this it might be the heat in that compartment, I probably should pull out the infrared thermometer and check what's going on.
>
> Thanks!
>
> --- In TekScopes@..., "Tom Jobe" wrote:
> >
> > For whatever reason, the three capacitors in the right rear corner of the mainboard fail on the 22xx scopes with your kind of power supply (C925, C942, C943) but they are easy to change without removing anything. Also in the same corner of the mainboard the SCR Q935 often fails on 22xx scopes, but your 2235A probably has the upgraded MCR72-4 SCR just like this one has, so you may have no worries there. I was just looking inside of this 2235A power supply to see how it differs from an ordinary 2235 and it is all quite similar, but upgraded in several ways.
> > tom jobe...
> >
> >
> > ----- Original Message -----
> > From: vdonisa
> > To: TekScopes@...
> > Sent: Saturday, March 30, 2013 8:57 AM
> > Subject: [TekScopes] Tek 2235A re-cap
> >
> >
> >
> > Hi All,
> >
> > I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)
> >
> > The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.
> >
> > What I noticed:
> >
> > - there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)
> >
> > - C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)
> >
> > - all other caps were looking OK
> >
> > For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.
> >
> > Now for the questions:
> >
> > - does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)
> >
> > - there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?
> >
> > - looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?
> >
> > - any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?
> >
> > - anything else that you gentlemen know to be frequently failing and should be replaced?
> >
> > Thanks!
> >
>


vdonisa
 

Hi Tom,

I already did, all electrolytic caps in the power supply were replaced with new, long life, 105C rated Panasonic and Rubycon. I was just musing that if that still doesn't work then I might go for 125 Celsius automotive rated ones :-)

But then I think the fan solution makes the most sense. As you mentioned, the 3 damaged caps were all having something in common - close proximity to the same heat sink (on one side or the other of it). A fan would blow right into that heat sink and help keep everything much cooler....

I just measured the distance between the holes and it appears that a 60mm fan (50mm hole distance) would fit just right. Mouser has in stock stuff like Ebm Papst 612FL - 12V, 0.4W, 11.2cfm, 16dBA - seems just right as a low noise solution. I'll wait though until you can get a look at the fan specs for the 2236A so I could know the proper voltage and max power it could draw. BTW I got my manuals from exactly the same source (together with a trigger knob) :-)

Thanks,
Valentin

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@...> wrote:

Hi Valentin,
Do yourself a favor and change those three capacitors in the right rear corner. If your scope has cooked C970 on the front side of the heat sink, things have been getting very hot in there.
I don't have a copy of the 2236A service manual so I ordered one today from Qservice in Greece. I would like to see what component values are specified for the 2236A fan supply.
This very nice 2235A I have had some ordinary problems in the power supply which I fixed a year or two ago. It had one remaining problem with channel 2 which had not been fixed. It turns out that U180 was dead in the vertical amplifier, so I replaced it with the similar part out of a 2235 (which has a different part number). The channel 2 voltage gain is now too low, so I removed the U180 that came from the 2235 and ordered the proper U180 part number for the 2235A.
It will be a week or two before the U180 part and the 2236A service manual arrive. I will let you know what I find out about this fan mod, etc.
tom jobe...
PS If anyone has a 2236A service manual, could I get you to look up the values of a few components in the electrical parts list?



----- Original Message -----
From: vdonisa
To: TekScopes@yahoogroups.com
Sent: Monday, April 01, 2013 2:39 PM
Subject: [TekScopes] Re: Tek 2235A re-cap



Hi Tom,

Thanks for your answer!

I was thinking of a fan too (a low noise low RPM one that would just move the air a little bit without sounding like a vacuum cleaner like my HP 3325A lol). But then I was not sure where I could connect it without disturbing the power supply too much. Now that I know.... I do remember that connector, with an empty place for a capacitor nearby, I just didn't know what exactly it was for.

Otherwise if I can't find a decent fan solution, I already identified some 10u/100V that should be able to take some heat: Nichicon has them in their BT series (automotive 125 Celsius) also Rubycon in RX30 series.

Thanks again!

Valentin

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@> wrote:
>
> Your observation that heat might be what kills those capacitors in the right rear corner of the mainboard, is probably worth considering.
> The 2235A has a much improved aluminum heat sink for Q946, Q947 and Q9070 which might further aggravate the situation for those capacitors, while helping the transistors and the MOSFET attached to the heat sink.
> Something you might consider is to use the onboard power supply for the 2236A case fan. The 2235A has the complete fan circuit less the capacitor C965. All of this is just in front of that aluminum heat sink, and the place for C965 is marked "2236A only". The back panel on the 2235A has a hole pattern to accept a standard 12 volt fan (50mm square bolt pattern on a 60mm diameter fan?), and the pins to connect the fan's power are just ahead of the heat sink and marked "W9965".
> If you look at the power supply schematic for a 2232 or a 2236A you will see the fan circuit and component numbers. I may have a copy of the fan schematic around here somewhere, but I think there is a free copy of the 2232 manual in several places. You don't even need the schematic if you decide to do this mod, just connect the fan with the polarity that moves the air in whichever direction you prefer.
> I have added this fan circuit to several 22xx scopes. Many of the older 22xx scopes had some kind of an undocumented fan circuit on the mainboard but you had to populate it. The 2215A and 2235 scopes would be examples that had the undocumented fan circuit.
> tom jobe...
>
>
>
> ----- Original Message -----
> From: vdonisa
> To: TekScopes@yahoogroups.com
> Sent: Saturday, March 30, 2013 6:19 PM
> Subject: [TekScopes] Re: Tek 2235A re-cap
>
>
>
> This is interesting, maybe the gentleman that replaced C942 & C943 with 4.7u/250V knew something, anyway his repair has lasted. In my case C925 was OK and looked like being the original one.
>
> Maybe I should find some 10u/250v although by looking at the schematic I can't understand how they would get so much voltage. Unless there's some weird transient action there at power turn on/off.
>
> Other than this it might be the heat in that compartment, I probably should pull out the infrared thermometer and check what's going on.
>
> Thanks!
>
> --- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@> wrote:
> >
> > For whatever reason, the three capacitors in the right rear corner of the mainboard fail on the 22xx scopes with your kind of power supply (C925, C942, C943) but they are easy to change without removing anything. Also in the same corner of the mainboard the SCR Q935 often fails on 22xx scopes, but your 2235A probably has the upgraded MCR72-4 SCR just like this one has, so you may have no worries there. I was just looking inside of this 2235A power supply to see how it differs from an ordinary 2235 and it is all quite similar, but upgraded in several ways.
> > tom jobe...
> >
> >
> > ----- Original Message -----
> > From: vdonisa
> > To: TekScopes@yahoogroups.com
> > Sent: Saturday, March 30, 2013 8:57 AM
> > Subject: [TekScopes] Tek 2235A re-cap
> >
> >
> >
> > Hi All,
> >
> > I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)
> >
> > The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.
> >
> > What I noticed:
> >
> > - there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)
> >
> > - C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)
> >
> > - all other caps were looking OK
> >
> > For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.
> >
> > Now for the questions:
> >
> > - does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)
> >
> > - there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?
> >
> > - looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?
> >
> > - any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?
> >
> > - anything else that you gentlemen know to be frequently failing and should be replaced?
> >
> > Thanks!
> >
>


vdonisa
 

It's me again... after doing a little bit more research (looking at other 2200 series oscilloscopes with fans) I came to the following conclusions:

- the case is designed so that the fan should be installed as an "exhaust" (outblow) fan; the air flow would be from the intake located on the left side near the middle of the CRT's length and gradually heat up until it flows along the hottest heat sink (the one between the 3 damaged caps) then gets exhausted through the rear vent

- installed like this it will also help with the power resistor located on the mainboard, under the CRT, near the intake - i saw some slight coloration of the PCB around it so I believe it heats up handsomely

This being said I'm tempted to go for:

- Sunon HA60251V4-000U-999 fan (13.8dBa)
installed on
- Qualtek QLM-60-30-10 vibration dampening sleeve

The fan draws only 60mA from 12V so it should not be such a burden for the power supply. Also Tek is using (beefier) Sunon fans in other 2200 series models so the brand would not look out of place in the 2235A.

Cheers,
Valentin

--- In TekScopes@yahoogroups.com, "vdonisa" <vdonisa@...> wrote:

Hi Tom,

I already did, all electrolytic caps in the power supply were replaced with new, long life, 105C rated Panasonic and Rubycon. I was just musing that if that still doesn't work then I might go for 125 Celsius automotive rated ones :-)

But then I think the fan solution makes the most sense. As you mentioned, the 3 damaged caps were all having something in common - close proximity to the same heat sink (on one side or the other of it). A fan would blow right into that heat sink and help keep everything much cooler....

I just measured the distance between the holes and it appears that a 60mm fan (50mm hole distance) would fit just right. Mouser has in stock stuff like Ebm Papst 612FL - 12V, 0.4W, 11.2cfm, 16dBA - seems just right as a low noise solution. I'll wait though until you can get a look at the fan specs for the 2236A so I could know the proper voltage and max power it could draw. BTW I got my manuals from exactly the same source (together with a trigger knob) :-)

Thanks,
Valentin

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@> wrote:

Hi Valentin,
Do yourself a favor and change those three capacitors in the right rear corner. If your scope has cooked C970 on the front side of the heat sink, things have been getting very hot in there.
I don't have a copy of the 2236A service manual so I ordered one today from Qservice in Greece. I would like to see what component values are specified for the 2236A fan supply.
This very nice 2235A I have had some ordinary problems in the power supply which I fixed a year or two ago. It had one remaining problem with channel 2 which had not been fixed. It turns out that U180 was dead in the vertical amplifier, so I replaced it with the similar part out of a 2235 (which has a different part number). The channel 2 voltage gain is now too low, so I removed the U180 that came from the 2235 and ordered the proper U180 part number for the 2235A.
It will be a week or two before the U180 part and the 2236A service manual arrive. I will let you know what I find out about this fan mod, etc.
tom jobe...
PS If anyone has a 2236A service manual, could I get you to look up the values of a few components in the electrical parts list?



----- Original Message -----
From: vdonisa
To: TekScopes@yahoogroups.com
Sent: Monday, April 01, 2013 2:39 PM
Subject: [TekScopes] Re: Tek 2235A re-cap



Hi Tom,

Thanks for your answer!

I was thinking of a fan too (a low noise low RPM one that would just move the air a little bit without sounding like a vacuum cleaner like my HP 3325A lol). But then I was not sure where I could connect it without disturbing the power supply too much. Now that I know.... I do remember that connector, with an empty place for a capacitor nearby, I just didn't know what exactly it was for.

Otherwise if I can't find a decent fan solution, I already identified some 10u/100V that should be able to take some heat: Nichicon has them in their BT series (automotive 125 Celsius) also Rubycon in RX30 series.

Thanks again!

Valentin

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@> wrote:
>
> Your observation that heat might be what kills those capacitors in the right rear corner of the mainboard, is probably worth considering.
> The 2235A has a much improved aluminum heat sink for Q946, Q947 and Q9070 which might further aggravate the situation for those capacitors, while helping the transistors and the MOSFET attached to the heat sink.
> Something you might consider is to use the onboard power supply for the 2236A case fan. The 2235A has the complete fan circuit less the capacitor C965. All of this is just in front of that aluminum heat sink, and the place for C965 is marked "2236A only". The back panel on the 2235A has a hole pattern to accept a standard 12 volt fan (50mm square bolt pattern on a 60mm diameter fan?), and the pins to connect the fan's power are just ahead of the heat sink and marked "W9965".
> If you look at the power supply schematic for a 2232 or a 2236A you will see the fan circuit and component numbers. I may have a copy of the fan schematic around here somewhere, but I think there is a free copy of the 2232 manual in several places. You don't even need the schematic if you decide to do this mod, just connect the fan with the polarity that moves the air in whichever direction you prefer.
> I have added this fan circuit to several 22xx scopes. Many of the older 22xx scopes had some kind of an undocumented fan circuit on the mainboard but you had to populate it. The 2215A and 2235 scopes would be examples that had the undocumented fan circuit.
> tom jobe...
>
>
>
> ----- Original Message -----
> From: vdonisa
> To: TekScopes@yahoogroups.com
> Sent: Saturday, March 30, 2013 6:19 PM
> Subject: [TekScopes] Re: Tek 2235A re-cap
>
>
>
> This is interesting, maybe the gentleman that replaced C942 & C943 with 4.7u/250V knew something, anyway his repair has lasted. In my case C925 was OK and looked like being the original one.
>
> Maybe I should find some 10u/250v although by looking at the schematic I can't understand how they would get so much voltage. Unless there's some weird transient action there at power turn on/off.
>
> Other than this it might be the heat in that compartment, I probably should pull out the infrared thermometer and check what's going on.
>
> Thanks!
>
> --- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@> wrote:
> >
> > For whatever reason, the three capacitors in the right rear corner of the mainboard fail on the 22xx scopes with your kind of power supply (C925, C942, C943) but they are easy to change without removing anything. Also in the same corner of the mainboard the SCR Q935 often fails on 22xx scopes, but your 2235A probably has the upgraded MCR72-4 SCR just like this one has, so you may have no worries there. I was just looking inside of this 2235A power supply to see how it differs from an ordinary 2235 and it is all quite similar, but upgraded in several ways.
> > tom jobe...
> >
> >
> > ----- Original Message -----
> > From: vdonisa
> > To: TekScopes@yahoogroups.com
> > Sent: Saturday, March 30, 2013 8:57 AM
> > Subject: [TekScopes] Tek 2235A re-cap
> >
> >
> >
> > Hi All,
> >
> > I just finished replacing a bunch of old aluminum capacitors in a recently received 2235A and I'm posting here to share my experience and ask a few questions. This is my first post here so please bear with me :-)
> >
> > The scope was in working status so it was about replacing any easily accessible capacitor in sight :-) So far I replaced only those located on the main board that can be accessed without removing the daughter boards. This means complete power supply cap replacement plus a few other cap spread elsewhere on the main board.
> >
> > What I noticed:
> >
> > - there was a previous repair work on C942 ad C943 (both 10u/100V), they were replaced with 4.7u/250V of types not normally found in a Tek; this looked like an old repair (not recent)
> >
> > - C970 (4700u/10V, +5V supply filter) was bulged and cracked at the base rubber vent and sitting in a weird position (because of the bulge lol)
> >
> > - all other caps were looking OK
> >
> > For replacements I used mainly Panasonic EEU-FR and EEU-ED series except C906 (Panasonic EET-ED) and the 10u/100V ones where I used Rubycon YXF.
> >
> > Now for the questions:
> >
> > - does this look like a decent choice of caps or could I have done better? (I'm looking at it as a "restoration of memorabilia" for myself; I'm interested in doing good work, cost is no objection)
> >
> > - there's a bunch of small electrolytics on the daughter boards, they seem to be mostly 22u/10V of Nichicon VX type, should I have a second session and replace these too? Are these prone to fail?
> >
> > - looking on the schematic C942 ad C943 don't seem to be stressed too much, any known reason why they failed and needed to be replaced (long time ago)? Should I over spec them (higher voltage than the original 100V)?
> >
> > - any good source for C906 270u/450V with 4 pins? I couldn't find any so I used a standard 10mm pin spaced snap-in, fortunately the PCB layout helped me and I was able to drill 2 extra holes and fit it there?
> >
> > - anything else that you gentlemen know to be frequently failing and should be replaced?
> >
> > Thanks!
> >
>


 

On Tue, 02 Apr 2013 15:02:28 -0000, "vdonisa" <vdonisa@yahoo.com>
wrote:

It's me again... after doing a little bit more research (looking at other 2200 series oscilloscopes with fans) I came to the following conclusions:

- the case is designed so that the fan should be installed as an "exhaust" (outblow) fan; the air flow would be from the intake located on the left side near the middle of the CRT's length and gradually heat up until it flows along the hottest heat sink (the one between the 3 damaged caps) then gets exhausted through the rear vent

- installed like this it will also help with the power resistor located on the mainboard, under the CRT, near the intake - i saw some slight coloration of the PCB around it so I believe it heats up handsomely
Those resistors are the load resistors for the output of the CRT
vertical amplifier and they do run hot. They are a common failure
point in the 22xx series oscilloscopes that lack fans. I replaced a
set not too long ago and someone on the list here has also done so
recently.

Some of the 22xx series use 3 resistors in series on each side instead
of 2 which distributes the heat load somewhat.


Tom Jobe <tomjobe@...>
 

On the later 22xx scopes (but before the 2235A, 2236A modifications) Tektronix raised some of the hot resistors under the CRT up off of the mainboard. From the "burn" marks you can see that a couple of the other resistors could use a bit of raising too.
Attached is a picture of Tektronix's later raised resistor solution, and another of the "homemade" raised resistors some of us have done on 22xx scopes. Also a picture of the mainboard burn spots is attached, the larger burn spot is from the resistors in question, the smaller burn spot is from the focus resistors that often fail on 22xx scopes. Many 22xx scopes have these burn spots on the mainboard.
tom jobe...
 
 
 

----- Original Message -----
From: David
Sent: Tuesday, April 02, 2013 9:37 AM
Subject: Re: [TekScopes] Re: Tek 2235A re-cap

 

On Tue, 02 Apr 2013 15:02:28 -0000, "vdonisa" <vdonisa@...>
wrote:

>It's me again... after doing a little bit more research (looking at other 2200 series oscilloscopes with fans) I came to the following conclusions:
>
>- the case is designed so that the fan should be installed as an "exhaust" (outblow) fan; the air flow would be from the intake located on the left side near the middle of the CRT's length and gradually heat up until it flows along the hottest heat sink (the one between the 3 damaged caps) then gets exhausted through the rear vent
>
>- installed like this it will also help with the power resistor located on the mainboard, under the CRT, near the intake - i saw some slight coloration of the PCB around it so I believe it heats up handsomely

Those resistors are the load resistors for the output of the CRT
vertical amplifier and they do run hot. They are a common failure
point in the 22xx series oscilloscopes that lack fans. I replaced a
set not too long ago and someone on the list here has also done so
recently.

Some of the 22xx series use 3 resistors in series on each side instead
of 2 which distributes the heat load somewhat.


vdonisa
 

Yes Sir, my PCB has that large brown spot exactly like in the right side of the 3rd photo... maybe not that dark brown but easily visible anyway.

Digikey just got an order for a fan + vibration dampener, it definitely seems to be the best solution.

Thanks all again for your explanations and suggestions!

Valentin

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@...> wrote:

On the later 22xx scopes (but before the 2235A, 2236A modifications) Tektronix raised some of the hot resistors under the CRT up off of the mainboard. From the "burn" marks you can see that a couple of the other resistors could use a bit of raising too.
Attached is a picture of Tektronix's later raised resistor solution, and another of the "homemade" raised resistors some of us have done on 22xx scopes. Also a picture of the mainboard burn spots is attached, the larger burn spot is from the resistors in question, the smaller burn spot is from the focus resistors that often fail on 22xx scopes. Many 22xx scopes have these burn spots on the mainboard.
tom jobe...



----- Original Message -----
From: David
To: TekScopes@yahoogroups.com
Sent: Tuesday, April 02, 2013 9:37 AM
Subject: Re: [TekScopes] Re: Tek 2235A re-cap



On Tue, 02 Apr 2013 15:02:28 -0000, "vdonisa" <vdonisa@...>
wrote:

>It's me again... after doing a little bit more research (looking at other 2200 series oscilloscopes with fans) I came to the following conclusions:
>
>- the case is designed so that the fan should be installed as an "exhaust" (outblow) fan; the air flow would be from the intake located on the left side near the middle of the CRT's length and gradually heat up until it flows along the hottest heat sink (the one between the 3 damaged caps) then gets exhausted through the rear vent
>
>- installed like this it will also help with the power resistor located on the mainboard, under the CRT, near the intake - i saw some slight coloration of the PCB around it so I believe it heats up handsomely

Those resistors are the load resistors for the output of the CRT
vertical amplifier and they do run hot. They are a common failure
point in the 22xx series oscilloscopes that lack fans. I replaced a
set not too long ago and someone on the list here has also done so
recently.

Some of the 22xx series use 3 resistors in series on each side instead
of 2 which distributes the heat load somewhat.


vdonisa
 


vdonisa
 

Part list for re-cap. It covers all the easily accessible aluminum caps on the main board and trigger board. It does not cover the caps located on the cluster of daughter boards near the front panel which is more difficult to dis/re assemble.

All part nr are manufacturer part numbers.

10u/100V Rubycon 100YXF10MEFC6.3X11 3 pcs A1C942, A1C943, A1C956

22u/50V Panasonic EEU-FR1H220 5pcs A1C292, A1C540, A1C646, A5C606, A5C641

33u/160V Panasonic EEU-ED2C330 1 pcs A1C954

100u/25V Panasonic EEU-FR1E101 1pcs A1C925

270u/50V Panasonic EEU-FR1H271 2pcs A1C881, A1C957

270u/450V Panasonic EET-ED2W271DA 1pcs A1C906 has only 2 pins need to shift position and drill 2 extra holes

1000u/16V Panasonic EEU-FR1C102 5pcs A1C960, A1C961, A1C962, A1C963, A1C968

1000u/50V Panasonic EEU-FR1H102 1pcs A1C940

4700u/10V Panasonic EEU-FR1A472S 1 pcs A1C970

If you want to address the 3 heat stressed capacitors circled in red with 125/130 Celsius rated parts, an alternative recommendation would be:

10u/100V Rubycon 100RX3010MTA8X11.5 3 pcs A1C942, A1C943, A1C956 (130 Celsius rated)

4700u/16V Nichicon UBT1C472MHD 1 pcs A1C970 (125 Celsius rated)

Also if you plan a replacement of the X2 and Y2 caps (located under the power plug and inside the line filter), the parts are:

68nF/275V Kemet PME271M568MR30 1pcs
2.2nF/250V Kemet PME271Y422MR30 2pcs

Cheers,
Valentin VE3VDO


vdonisa
 


Hi All,

I've since done some more research on the available 10uF/100V+ capacitors, and now I believe that for this power supply where they are particularly prone to failure, a better choice might be  Nichicon UCA2C100MPD1TD as seen in this photo:

http://groups.yahoo.com/group/TekScopes/photos/album/1314606778/pic/405367259/view

So I would like to add here a recommendation for the Nichicon UCA2C100MPD1TD as a subsitute for the original 10uF/100V caps.

Cheers,
Valentin VE3VDO


--- In TekScopes@..., "vdonisa" wrote:
>
> Part list for re-cap. It covers all the easily accessible aluminum caps on the main board and trigger board. It does not cover the caps located on the cluster of daughter boards near the front panel which is more difficult to dis/re assemble.
>
> All part nr are manufacturer part numbers.
>
> 10u/100V Rubycon 100YXF10MEFC6.3X11 3 pcs A1C942, A1C943, A1C956
>
> 22u/50V Panasonic EEU-FR1H220 5pcs A1C292, A1C540, A1C646, A5C606, A5C641
>
> 33u/160V Panasonic EEU-ED2C330 1 pcs A1C954
>
> 100u/25V Panasonic EEU-FR1E101 1pcs A1C925
>
> 270u/50V Panasonic EEU-FR1H271 2pcs A1C881, A1C957
>
> 270u/450V Panasonic EET-ED2W271DA 1pcs A1C906 has only 2 pins need to shift position and drill 2 extra holes
>
> 1000u/16V Panasonic EEU-FR1C102 5pcs A1C960, A1C961, A1C962, A1C963, A1C968
>
> 1000u/50V Panasonic EEU-FR1H102 1pcs A1C940
>
> 4700u/10V Panasonic EEU-FR1A472S 1 pcs A1C970
>
> If you want to address the 3 heat stressed capacitors circled in red with 125/130 Celsius rated parts, an alternative recommendation would be:
>
> 10u/100V Rubycon 100RX3010MTA8X11.5 3 pcs A1C942, A1C943, A1C956 (130 Celsius rated)
>
> 4700u/16V Nichicon UBT1C472MHD 1 pcs A1C970 (125 Celsius rated)
>
> Also if you plan a replacement of the X2 and Y2 caps (located under the power plug and inside the line filter), the parts are:
>
> 68nF/275V Kemet PME271M568MR30 1pcs
> 2.2nF/250V Kemet PME271Y422MR30 2pcs
>
> Cheers,
> Valentin VE3VDO
>


vdonisa
 

Hi All,

Since the capacitor forensics in the 2467B was quite popular here, I decided to do the measurements on the caps extracted from the 2235A too. They were in much worse shape, only two or three of them were passable. Obviously this scope had many more hours on it. The interesting thing was to find that those innocuous looking small blue Nichicons VX spread all over the mainboard (not in the power supply) were quite worn out too. I'm mentioning this since the general recommendation is to not bother replacing them.

So lets get to the list. First column capacity in uF, second column dissipation factor, measurements at 100Hz.

Big can 5 pin snap-in brown Nichicon 270u/450V nominal (original):

256.3 0.062

Original Tektronix labeled 3 pin nominal 1000uf/12V:

1542.9 0.118
1466.6 0.143
1563.6 0.632
1533.1 0.416
1545.3 0.902 (did not vent/leak though)

original Tek 270u/40V:

330 0.079

replacement for another 270/40V from previous repair, orange Sprague 220/63:

196.7 0.045

United Chemi 1000u/50V:

896.2 0.108

Blue original "USA" 4700/10:

3812 0.463 this one had bulge and big crack at bottom rubber vent, did not leak though; probably had slowly dried

United 4.7/250V:

5.36 0.07

Two capacitors of 4.7/250 used in previous old repair to replace 10/100, the two ones that are prone to failure:

5.36 0.07
4.08 0.029 (nice, this was an axial orange "Sprague Atom")

Nichicon 33u/160V

34.49 0.037

United 10u/100V:

10.58 0.071

Nichicon VX 100/25:

70.28 0.194

Nichicon VX 22/10:

21.15 0.055
18.98 0.086
20.80 0.066
17.46 0.098
18.17 0.099

pretty high.

Note for Tom J.: since your Y2 caps measured as high as 3n - like mine - judging by their degradation there's a good chance that your electrolytics are in similar shape too. Time to heat the iron :-)

Cheers,
Valentin VE3VDO


Tom Jobe <tomjobe@...>
 

Thanks Valentin!
Your results show it is all worse than I thought.
It's time to change some more capacitors!
tom jobe...
 
 
 

----- Original Message -----
From: vdonisa
Sent: Wednesday, April 17, 2013 5:01 PM
Subject: [TekScopes] Re: Tek 2235A re-cap

 

Hi All,

Since the capacitor forensics in the 2467B was quite popular here, I decided to do the measurements on the caps extracted from the 2235A too. They were in much worse shape, only two or three of them were passable. Obviously this scope had many more hours on it. The interesting thing was to find that those innocuous looking small blue Nichicons VX spread all over the mainboard (not in the power supply) were quite worn out too. I'm mentioning this since the general recommendation is to not bother replacing them.

So lets get to the list. First column capacity in uF, second column dissipation factor, measurements at 100Hz.

Big can 5 pin snap-in brown Nichicon 270u/450V nominal (original):

256.3 0.062

Original Tektronix labeled 3 pin nominal 1000uf/12V:

1542.9 0.118
1466.6 0.143
1563.6 0.632
1533.1 0.416
1545.3 0.902 (did not vent/leak though)

original Tek 270u/40V:

330 0.079

replacement for another 270/40V from previous repair, orange Sprague 220/63:

196.7 0.045

United Chemi 1000u/50V:

896.2 0.108

Blue original "USA" 4700/10:

3812 0.463 this one had bulge and big crack at bottom rubber vent, did not leak though; probably had slowly dried

United 4.7/250V:

5.36 0.07

Two capacitors of 4.7/250 used in previous old repair to replace 10/100, the two ones that are prone to failure:

5.36 0.07
4.08 0.029 (nice, this was an axial orange "Sprague Atom")

Nichicon 33u/160V

34.49 0.037

United 10u/100V:

10.58 0.071

Nichicon VX 100/25:

70.28 0.194

Nichicon VX 22/10:

21.15 0.055
18.98 0.086
20.80 0.066
17.46 0.098
18.17 0.099

pretty high.

Note for Tom J.: since your Y2 caps measured as high as 3n - like mine - judging by their degradation there's a good chance that your electrolytics are in similar shape too. Time to heat the iron :-)

Cheers,
Valentin VE3VDO


vdonisa
 

Yes, after seeing this I think I'll replace the small VX caps on the difficult-to-dissasemble daughter boards too. I was secretly hoping I don't need to :-)

--- In TekScopes@yahoogroups.com, "Tom Jobe" <tomjobe@...> wrote:

Thanks Valentin!
Your results show it is all worse than I thought.
It's time to change some more capacitors!
tom jobe...



----- Original Message -----
From: vdonisa
To: TekScopes@yahoogroups.com
Sent: Wednesday, April 17, 2013 5:01 PM
Subject: [TekScopes] Re: Tek 2235A re-cap



Hi All,

Since the capacitor forensics in the 2467B was quite popular here, I decided to do the measurements on the caps extracted from the 2235A too. They were in much worse shape, only two or three of them were passable. Obviously this scope had many more hours on it. The interesting thing was to find that those innocuous looking small blue Nichicons VX spread all over the mainboard (not in the power supply) were quite worn out too. I'm mentioning this since the general recommendation is to not bother replacing them.

So lets get to the list. First column capacity in uF, second column dissipation factor, measurements at 100Hz.

Big can 5 pin snap-in brown Nichicon 270u/450V nominal (original):

256.3 0.062

Original Tektronix labeled 3 pin nominal 1000uf/12V:

1542.9 0.118
1466.6 0.143
1563.6 0.632
1533.1 0.416
1545.3 0.902 (did not vent/leak though)

original Tek 270u/40V:

330 0.079

replacement for another 270/40V from previous repair, orange Sprague 220/63:

196.7 0.045

United Chemi 1000u/50V:

896.2 0.108

Blue original "USA" 4700/10:

3812 0.463 this one had bulge and big crack at bottom rubber vent, did not leak though; probably had slowly dried

United 4.7/250V:

5.36 0.07

Two capacitors of 4.7/250 used in previous old repair to replace 10/100, the two ones that are prone to failure:

5.36 0.07
4.08 0.029 (nice, this was an axial orange "Sprague Atom")

Nichicon 33u/160V

34.49 0.037

United 10u/100V:

10.58 0.071

Nichicon VX 100/25:

70.28 0.194

Nichicon VX 22/10:

21.15 0.055
18.98 0.086
20.80 0.066
17.46 0.098
18.17 0.099

pretty high.

Note for Tom J.: since your Y2 caps measured as high as 3n - like mine - judging by their degradation there's a good chance that your electrolytics are in similar shape too. Time to heat the iron :-)

Cheers,
Valentin VE3VDO