465B recapping and tantalum caps


pdxareaid
 

Greetings 465/465B repairers and recappers.
I have just spent time with a couple of broken 465B's and thought I'd pass along the experience.

1. Recapping low PS
I recapped the low power supplies and used the ebay discs to install snap-in caps. https://www.ebay.com/itm/273254508468
I now regret having used those discs.
After I ordered the discs, I noticed a TekScopes member "n4buq" had a much better solution (bravo!) and may still in fact
offer his standoff board for sale. If not, it could be made with a low tech copper-clad hole board, resist pen and etch acid.
With that solution, everything is easily accessible.
I did, in fact, break one trace, not discovering it until after the new discs/caps were installed.
Even though I did a continuity check to avoid exactly this, I think I damaged the trace when doing some minor work nearby just before cap installation.
I had to jump the trace off the board for a fix. I could have easily fixed it on the A4 board if I had used his standoff board solution.
n4buq writeup https://groups.io/g/TekScopes/files/Replacing%20Electrolytic%20Filter%20Capacitors%20in%20a%20Tektronix%20465.pdf

2. Tantalum Caps
Years ago I put together an HTML file identifying the dipped tantalum caps that tend to fail so often.
I lost access to it in the Yahoo/GroupsIO move but that has been fixed recently.
I have uploaded an updated HTML file with the following addition (as well as updated contact info):
C4331 47uF 20V with a note. It is a confusing one. Should it be a tant or a film cap? Read the note.
The file is https://groups.io/g/TekScopes/files/465Btants.html

3. Mysterious Cap
While I was scratching my head over 2. above, I notice a tiny dipped tant on all three of my (early build) A4 boards. I had missed it in the original
survey. I tried to look it up in the manual (ARTEK early build 465B) but it is not there. The pads are there but the tant does not show up.
I looked for an add/delete change in the manual but did not see any appropriate.
I think it is a filter cap in the horizonal amplifier circuitry but it is not in the diagram either.
It physically sits between R4373 and R4374 on the A4 board. The pads are even on the manual's A4 diagram, but no cap.
If that thing shorts, it is going to be one confusing debug.
Here is a pic of it https://groups.io/g/TekScopes/photo/269282/3324900
Does anyone know what is going on here? Can anyone identify this cap and point to Tek documentation?


n4buq
 

I do still have some of those boards available.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "pdxareaid via groups.io" <mousterious=yahoo.com@groups.io>
To: "tekscopes" <TekScopes@groups.io>
Sent: Saturday, October 23, 2021 4:29:14 AM
Subject: [TekScopes] 465B recapping and tantalum caps
Greetings 465/465B repairers and recappers.
I have just spent time with a couple of broken 465B's and thought I'd pass along
the experience.

1. Recapping low PS
I recapped the low power supplies and used the ebay discs to install snap-in
caps. https://www.ebay.com/itm/273254508468
I now regret having used those discs.
After I ordered the discs, I noticed a TekScopes member "n4buq" had a much
better solution (bravo!) and may still in fact
offer his standoff board for sale. If not, it could be made with a low tech
copper-clad hole board, resist pen and etch acid.
With that solution, everything is easily accessible.
I did, in fact, break one trace, not discovering it until after the new
discs/caps were installed.
Even though I did a continuity check to avoid exactly this, I think I damaged
the trace when doing some minor work nearby just before cap installation.
I had to jump the trace off the board for a fix. I could have easily fixed it
on the A4 board if I had used his standoff board solution.
n4buq writeup
https://groups.io/g/TekScopes/files/Replacing%20Electrolytic%20Filter%20Capacitors%20in%20a%20Tektronix%20465.pdf

2. Tantalum Caps
Years ago I put together an HTML file identifying the dipped tantalum caps that
tend to fail so often.
I lost access to it in the Yahoo/GroupsIO move but that has been fixed recently.
I have uploaded an updated HTML file with the following addition (as well as
updated contact info):
C4331 47uF 20V with a note. It is a confusing one. Should it be a tant or a
film cap? Read the note.
The file is https://groups.io/g/TekScopes/files/465Btants.html

3. Mysterious Cap
While I was scratching my head over 2. above, I notice a tiny dipped tant on
all three of my (early build) A4 boards. I had missed it in the original
survey. I tried to look it up in the manual (ARTEK early build 465B) but it is
not there. The pads are there but the tant does not show up.
I looked for an add/delete change in the manual but did not see any appropriate.
I think it is a filter cap in the horizonal amplifier circuitry but it is not in
the diagram either.
It physically sits between R4373 and R4374 on the A4 board. The pads are even
on the manual's A4 diagram, but no cap.
If that thing shorts, it is going to be one confusing debug.
Here is a pic of it https://groups.io/g/TekScopes/photo/269282/3324900
Does anyone know what is going on here? Can anyone identify this cap and point
to Tek documentation?



Mark Vincent
 

C4331 is 47mfd. It should be 25V or 35V. Using a larger value, 100mfd 25V ULD for example, will work.

The mysterious cap you mention is a 50 ohm thermistor in parallel with the 27 ohm resistor.

Mark


pdxareaid
 

"The mysterious cap you mention is a 50 ohm thermistor in parallel with the 27 ohm resistor."

thanks Mark. I have seen no documentation of that thermistor. How do you know this? Where can i look? Did i just miss something simple?


pdxareaid
 

On Sat, Oct 23, 2021 at 08:00 AM, Mark Vincent wrote:


C4331 is 47mfd. It should be 25V or 35V. Using a larger value, 100mfd 25V ULD
for example, will work.
I agree the V rating should be higher. even 25V seems a little low but 35+ is likely sufficient.


pdxareaid
 

On Sat, Oct 23, 2021 at 10:00 AM, pdxareaid wrote:


"The mysterious cap you mention is a 50 ohm thermistor in parallel with the 27
ohm resistor."

thanks Mark. I have seen no documentation of that thermistor. How do you know
this? Where can i look? Did i just miss something simple?
Ahhh...i see it now in the circuit diagram. it is just not depicted on the A4 board for some reason. Thanks.


Ozan
 

On Sat, Oct 23, 2021 at 10:12 AM, pdxareaid wrote:


On Sat, Oct 23, 2021 at 10:00 AM, pdxareaid wrote:


"The mysterious cap you mention is a 50 ohm thermistor in parallel with the
27
ohm resistor."

thanks Mark. I have seen no documentation of that thermistor. How do you
know
this? Where can i look? Did i just miss something simple?
Ahhh...i see it now in the circuit diagram. it is just not depicted on the A4
board for some reason. Thanks.
-------

It is RT4373, on A4 board diagram it is shown to the left of R4373 trimpot. In your picture if you look at the same location there are two empty solder islands, instead the thermistor is in the "mystery component" location. Tracing connection in the picture shows it is parallel to R4374 (27-ohm) which matches the schematic. It looks like there are two alternate locations for the thermistor.

Ozan


pdxareaid
 

On Sat, Oct 23, 2021 at 11:02 AM, Ozan wrote:


It looks like there are two alternate locations for the thermistor.
yep, i see that now. odd but REALLY resolved now. thanks, phil


David Austerman
 

Barry-
I haven't looked and compared 465 and 465B board layouts on the prints, but I figure you might have been down the road before of being asked if these are compatible with a 465? If so, how would I obtain one of these? Do you have a website? I have a 465 that is working fine with original electros right now anyway, but you know how that goes. I'd like to maybe get ahead of the problem, or at the very least be ready if I put it off until that fateful day. I might actually not procrastinate if I had a nice little board!
Thanks, dave austerman KG5IPO


n4buq
 

Hi Dave,

I think the subject has come up and I _think_ the filter sections for both are the same - or at least with very little changes but I can't really be sure.

Send me your address and I'll get a board out to you if you still want one. You can send me a couple of bucks to cover costs if you want but not a big deal.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "David Austerman" <737builder@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Sunday, October 24, 2021 4:49:48 PM
Subject: Re: [TekScopes] 465B recapping and tantalum caps
Barry-
I haven't looked and compared 465 and 465B board layouts on the prints, but I
figure you might have been down the road before of being asked if these are
compatible with a 465? If so, how would I obtain one of these? Do you have a
website? I have a 465 that is working fine with original electros right now
anyway, but you know how that goes. I'd like to maybe get ahead of the problem,
or at the very least be ready if I put it off until that fateful day. I might
actually not procrastinate if I had a nice little board!
Thanks, dave austerman KG5IPO



David Austerman
 

Thanks Barry!
I can paypal you some money for the board and shipping. I can email you my address or whatever you think is the safest way to exchange info. I will need to get your paypal send-to address. My email is 737builder-at-gmail.com. I appreciate it.
73


barry.ballenger@...
 

You got wrong person my call is KD0MUY and don’t have any boards. Sorry for
mixup

On Wed, Oct 27, 2021 at 11:43 PM David Austerman <737builder@gmail.com>
wrote:

Thanks Barry!
I can paypal you some money for the board and shipping. I can email you my
address or whatever you think is the safest way to exchange info. I will
need to get your paypal send-to address. My email is
737builder-at-gmail.com. I appreciate it.
73