Topics

Just got a 475, nothing showing on display


donald collie
 

Don`t keep us in suspence Jake, how are you going with your 475? [I have
one of these too]
Cheers!...................................................................Donald

On Fri, Jul 31, 2020 at 11:53 AM Steph L <stephlan@...> wrote:

Crt filament not open?




Steph L
 

Crt filament not open?


Michael W. Lynch
 

On Thu, Jul 30, 2020 at 09:35 AM, David Kuhn wrote:


" Change ALL tantalum caps"

Tantalum? Unless they are shorted and burned, why woiuld you change a
bunch of tantalums? Granted they can put off a firework show when they
blow, but that's fairly rare. I've had more brand news ones pop than old
ones (probable black bar marked on wrong end).
David,

I wholeheartedly agree. This is where my comment about "shotgun" repairs above originated. Just to make the scope operate, it is way too much trouble and expense to just wholesale replace them all. The tantalum caps will generally let you know when they are bad. My practice is to replace obviously burned or discolored dry ones or leaking, burned or discolored cases on the wet ones. Once this is done, then diagnosis on the individual circuits may lead you to other components that have less obvious failures. This method works very well for me.

Best of luck!

--
Michael Lynch
Dardanelle, AR


Renée
 

years ago I ( We-the company i worked for) had a batch come into the production line that were marked incorrectly...what a pain that was!
Renée

On 7/30/20 8:29 AM, Chuck Harris wrote:
You are aware that the polarity marker on tantalum
capacitors is always the "+" terminal, right?

-Chuck Harris

David Kuhn wrote:
" Change ALL tantalum caps"

Tantalum? Unless they are shorted and burned, why woiuld you change a
bunch of tantalums? Granted they can put off a firework show when they
blow, but that's fairly rare. I've had more brand news ones pop than old
ones (probable black bar marked on wrong end).

Dave

On Wed, Jul 29, 2020 at 2:48 AM Alexandre Souza <
alexandre.tabajara@...> wrote:

Change ALL tantalum caps. Probably it will work =)

---8<---Corte aqui---8<---
http://www.tabajara-labs.blogspot.com
http://www.tabalabs.com.br
---8<---Corte aqui---8<---


Em ter., 28 de jul. de 2020 às 18:24, <jakenicholasward@...>
escreveu:

Hey guys,

I just got a Tektronix 475 from ebay. The fan spins, lights come on, but
there’s no trace and no dot when I hit “beam finder”. I measured the
power
supply test points and got these results:

+5: 4.99v, 48.5 ohm to ground, 0mv ripple voltage
-8: -7.96v, 40.8 ohm, 0mv ripple
+15: 14.98v, 68 ohm, 4mv ripple
+50: 50.00v, 2.78k ohm, 36v* ripple
+50 unregulated: 67v, OL, 31.9v* ripple
+105/160: 139.4v, OL, 13.8v* ripple
+110: 111.1v, OL, 20.9v* ripple

* where I measured high ripple voltages, my multimeter switched back and
forth from That voltage to zero in about 1 second intervals. Not sure
what
that means.

The resistance on the +5, -8, and +15 volt rails seems very low, is that
normal? I didn’t see any expected values in the service manual (although
I
haven’t read too deep).

I also noticed some kind of corrosion around where the giant caps(?) are.

It might be worth noting that the beam finder seemed to work on the ebay
listing, but I haven’t been able to make it work.

I’m new here and fairly new to electronics in general so I’d appreciate
any help. Thanks!






Chuck Harris
 

You are aware that the polarity marker on tantalum
capacitors is always the "+" terminal, right?

-Chuck Harris

David Kuhn wrote:

" Change ALL tantalum caps"

Tantalum? Unless they are shorted and burned, why woiuld you change a
bunch of tantalums? Granted they can put off a firework show when they
blow, but that's fairly rare. I've had more brand news ones pop than old
ones (probable black bar marked on wrong end).

Dave

On Wed, Jul 29, 2020 at 2:48 AM Alexandre Souza <
alexandre.tabajara@...> wrote:

Change ALL tantalum caps. Probably it will work =)

---8<---Corte aqui---8<---
http://www.tabajara-labs.blogspot.com
http://www.tabalabs.com.br
---8<---Corte aqui---8<---


Em ter., 28 de jul. de 2020 às 18:24, <jakenicholasward@...>
escreveu:

Hey guys,

I just got a Tektronix 475 from ebay. The fan spins, lights come on, but
there’s no trace and no dot when I hit “beam finder”. I measured the
power
supply test points and got these results:

+5: 4.99v, 48.5 ohm to ground, 0mv ripple voltage
-8: -7.96v, 40.8 ohm, 0mv ripple
+15: 14.98v, 68 ohm, 4mv ripple
+50: 50.00v, 2.78k ohm, 36v* ripple
+50 unregulated: 67v, OL, 31.9v* ripple
+105/160: 139.4v, OL, 13.8v* ripple
+110: 111.1v, OL, 20.9v* ripple

* where I measured high ripple voltages, my multimeter switched back and
forth from That voltage to zero in about 1 second intervals. Not sure
what
that means.

The resistance on the +5, -8, and +15 volt rails seems very low, is that
normal? I didn’t see any expected values in the service manual (although
I
haven’t read too deep).

I also noticed some kind of corrosion around where the giant caps(?) are.

It might be worth noting that the beam finder seemed to work on the ebay
listing, but I haven’t been able to make it work.

I’m new here and fairly new to electronics in general so I’d appreciate
any help. Thanks!








David Kuhn
 

" Change ALL tantalum caps"

Tantalum? Unless they are shorted and burned, why woiuld you change a
bunch of tantalums? Granted they can put off a firework show when they
blow, but that's fairly rare. I've had more brand news ones pop than old
ones (probable black bar marked on wrong end).

Dave

On Wed, Jul 29, 2020 at 2:48 AM Alexandre Souza <
alexandre.tabajara@...> wrote:

Change ALL tantalum caps. Probably it will work =)

---8<---Corte aqui---8<---
http://www.tabajara-labs.blogspot.com
http://www.tabalabs.com.br
---8<---Corte aqui---8<---


Em ter., 28 de jul. de 2020 às 18:24, <jakenicholasward@...>
escreveu:

Hey guys,

I just got a Tektronix 475 from ebay. The fan spins, lights come on, but
there’s no trace and no dot when I hit “beam finder”. I measured the
power
supply test points and got these results:

+5: 4.99v, 48.5 ohm to ground, 0mv ripple voltage
-8: -7.96v, 40.8 ohm, 0mv ripple
+15: 14.98v, 68 ohm, 4mv ripple
+50: 50.00v, 2.78k ohm, 36v* ripple
+50 unregulated: 67v, OL, 31.9v* ripple
+105/160: 139.4v, OL, 13.8v* ripple
+110: 111.1v, OL, 20.9v* ripple

* where I measured high ripple voltages, my multimeter switched back and
forth from That voltage to zero in about 1 second intervals. Not sure
what
that means.

The resistance on the +5, -8, and +15 volt rails seems very low, is that
normal? I didn’t see any expected values in the service manual (although
I
haven’t read too deep).

I also noticed some kind of corrosion around where the giant caps(?) are.

It might be worth noting that the beam finder seemed to work on the ebay
listing, but I haven’t been able to make it work.

I’m new here and fairly new to electronics in general so I’d appreciate
any help. Thanks!






David Kuhn
 

" It makes no mention of being able to measure ripple values with a DMM"

Would not a DVm measure ripple in RMS mode? I always tend to measure
ripple in Peak to Peak mode with a scope. So any ripple you can measure
with a DVM you would multiply by 2.828??

Dave

On Wed, Jul 29, 2020 at 2:29 AM Brian Cockburn <
brian.cockburn.1959@...> wrote:

Hi,

Jake's point about having an issue or uncertainty about measuring ripple
with a multimeter reminded me about a similar question that's been in my
mind for a while.

In the service manual of the 2245A (the 'scope I have), Table 4-1 calls
for a 'DMM DC Volts range: 0 to 140 V. DC voltage accuracy: ±0.15%. 4½
digit display. e.g. Tektronix DM 501A'. It makes no mention of being able
to measure ripple values with a DMM, suggesting instead that a 'scope is
used. So is measuring ripple with a DMM valid? Is it useful given that
maximum allowable ripple is given for two distinct bands: 60-150 Hz and
20-40 kHz (which I take to mean 20 kHz to 40 kHz, rather than 20 Hz to 40
kHz). Do I need a DMM that 'goes' to at least 40 kHz on ACV to make a
useful measurement here?

For instance, my 5½ digit 220,000 count bench DMM claims to have a 3 dB
bandwidth of 300 kHz. On the 200 mVAC range it clearly doesn't meet the
required ±0.15% accuracy figure, but it's what I've got. (Accuracy is
given as %rdg + counts: 20 Hz to 50 Hz => 1.00 + 100, 50 Hz to 10 kHz =>
0.35 + 100, 10 kHz to 20 kHz => 0.6 + 200, 20 kHz to 50 kHz => 1.5 + 250,
50 kHz to 100 kHz => 5 + 400.) Do I just need to make the calculations
about my DMM's worst case error in each (of its) bands and make sure that
my measured value including the error is below the required (specified)
level?

Thanks, Brian.




Michael W. Lynch
 

On Wed, Jul 29, 2020 at 04:47 AM, donald collie wrote:

Is the fse on the main PCB at the back left blown? If so, it is almost
certain that the Tantalum capacitor associated with this circuit is
shorted......................Donald Collie
Check F1318 as Donald mentioned. Is it open? You should have 15V Unregulated at that fuse. If F1318 is open, check C1318, which is a tantalum cap in the primary of the HV transformer, this can short and stop the HV circuit from working. Check the power transistor Q1318, this is a common failure point as well on the same circuit.

+5: 4.99v, 48.5 ohm to ground, 0mv ripple voltage<
-8: -7.96v, 40.8 ohm, 0mv ripple<
+15: 14.98v, 68 ohm, 4mv ripple<
+50: 50.00v, 2.78k ohm, 36v* ripple<
+50 unregulated: 67v, OL, 31.9v* ripple<
+105/160: 139.4v, OL, 13.8v* ripple<
+110: 111.1v, OL, 20.9v* ripple<
Your Low Voltage power supplies seem to be working, the voltages are very close to ideal. Worry about ripple after later. You really need a scope to accurately measure ripple.

Concentrate on getting a spot or a trace. Shotgun replacement of parts which are not known or obviously bad is not the best way to proceed, replace only OBVIOUSLY burned or defective parts at this time.

Clean that beam finder switch with DE-OXIT or other cleaning method and exercise the switch, could be as simple as a dirty switch.

But it sounds like the same problem I have with a 465. I have a dead HV Multiplier<
Regarding the HV Multiplier that Stephen mentioned, this is also a very common failure which will open F1318. On most 465/475 Series scopes there is an isolation jumper on the ground or common side of the HV Multiplier, this can be a simple wire jumper or wire with a plain white ceramic insulator. If present on your scope, this jumper will be located under that HV shield of the bottom board near to and in front of the two nylon nuts that secure the HV Multiplier to the circuit board. This jumper is often not clearly identified in the manual. If you have this jumper, carefully unsolder and lift one end. This will take the HV multiplier out of circuit and allow the HV Transformer to generate the -3kV required for the CRT to partially function . Once the Multiplier is out of circuit, you should be able to observe some sort of visual reaction from the CRT, such as a short trace, a dot or a faint glow (depending on other failures).

WARNING: Keep in mind that you may now have potentials in excess of 3kV present IF you do this step and the HV Circuit comes back to life. Extreme care should be used when working on any component located under that HV Shield as High voltages may remain, even after the power is switched off.

Make sure that you have the correct version of the Service Manual for your scope. Study the Theory of Operation, Schematics and the Circuit descriptions. Do not attempt to proceed without the proper manual, either paper or digital.

A last recommendation (from someone who has been there recently): Focus on one problem at a time, do not try to diagnose/fix everything at once. Systematic diagnosis and repair yields the best results, As I stated previously, "wholesale" or "shotgun" replacement of components is not the most effective way to fix the problem. One lesson that I learned, REGARDLESS of the brand or type of equipment is that you must have the correct power supply voltages at all test points of the supply before proceeding to repair other faults. On this point, you seem to be on track.

Good Luck!

--
Michael Lynch
Dardanelle, AR


donald collie
 

Is the fse on the main PCB at the back left blown? If so, it is almost
certain that the Tantalum capacitor associated with this circuit is
shorted......................Donald Collie

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On Wed, Jul 29, 2020 at 9:24 PM Roger Evans via groups.io <very_fuzzy_logic=
yahoo.com@groups.io> wrote:

The high ripple you measure on the 50V and 100+ Volt supplies is usually
due to the large 'bulk' smoothing capacitors on those supplies drying out
with age and simultaneously losing their capacitance and developing high
series resistance. Both these changes render them ineffective at removing
the ripple at the output of the rectifiers. C1414 is almost certainly the
main culprit, C1412 is suspect but might be OK (it is a somewhat unusual
smoothing arrangement). You can make a temporary fix by using a modern
electrolytic capacitor and attaching it in parallel to the existing
capacitor, if necessary using some short leads to position the new
capacitor out of harm's way. The new cap needs to the same or higher
voltage rating and the same or slightly larger capacitance.

Failed tantalum capacitors usually fail short circuit and pull the suply
rail to almost zero volts. They are a perennial problem with old equipment.

Regards,

Roger




Roger Evans
 

The high ripple you measure on the 50V and 100+ Volt supplies is usually due to the large 'bulk' smoothing capacitors on those supplies drying out with age and simultaneously losing their capacitance and developing high series resistance. Both these changes render them ineffective at removing the ripple at the output of the rectifiers. C1414 is almost certainly the main culprit, C1412 is suspect but might be OK (it is a somewhat unusual smoothing arrangement). You can make a temporary fix by using a modern electrolytic capacitor and attaching it in parallel to the existing capacitor, if necessary using some short leads to position the new capacitor out of harm's way. The new cap needs to the same or higher voltage rating and the same or slightly larger capacitance.

Failed tantalum capacitors usually fail short circuit and pull the suply rail to almost zero volts. They are a perennial problem with old equipment.

Regards,

Roger


Stephen
 

On Tue, Jul 28, 2020 at 07:48 PM, Alexandre Souza wrote:


Change ALL tantalum caps. Probably it will work =)
Just a quick question that I’ve had for a while. Do you have to put back those little blue beads on the tantalum caps? They are not ferrite beads, I don’t think. They break like glass.


Alexandre Souza
 

Change ALL tantalum caps. Probably it will work =)

---8<---Corte aqui---8<---
http://www.tabajara-labs.blogspot.com
http://www.tabalabs.com.br
---8<---Corte aqui---8<---


Em ter., 28 de jul. de 2020 às 18:24, <jakenicholasward@...> escreveu:

Hey guys,

I just got a Tektronix 475 from ebay. The fan spins, lights come on, but
there’s no trace and no dot when I hit “beam finder”. I measured the power
supply test points and got these results:

+5: 4.99v, 48.5 ohm to ground, 0mv ripple voltage
-8: -7.96v, 40.8 ohm, 0mv ripple
+15: 14.98v, 68 ohm, 4mv ripple
+50: 50.00v, 2.78k ohm, 36v* ripple
+50 unregulated: 67v, OL, 31.9v* ripple
+105/160: 139.4v, OL, 13.8v* ripple
+110: 111.1v, OL, 20.9v* ripple

* where I measured high ripple voltages, my multimeter switched back and
forth from That voltage to zero in about 1 second intervals. Not sure what
that means.

The resistance on the +5, -8, and +15 volt rails seems very low, is that
normal? I didn’t see any expected values in the service manual (although I
haven’t read too deep).

I also noticed some kind of corrosion around where the giant caps(?) are.

It might be worth noting that the beam finder seemed to work on the ebay
listing, but I haven’t been able to make it work.

I’m new here and fairly new to electronics in general so I’d appreciate
any help. Thanks!




Brian Cockburn
 

Hi,

Jake's point about having an issue or uncertainty about measuring ripple with a multimeter reminded me about a similar question that's been in my mind for a while.

In the service manual of the 2245A (the 'scope I have), Table 4-1 calls for a 'DMM DC Volts range: 0 to 140 V. DC voltage accuracy: ±0.15%. 4½ digit display. e.g. Tektronix DM 501A'. It makes no mention of being able to measure ripple values with a DMM, suggesting instead that a 'scope is used. So is measuring ripple with a DMM valid? Is it useful given that maximum allowable ripple is given for two distinct bands: 60-150 Hz and 20-40 kHz (which I take to mean 20 kHz to 40 kHz, rather than 20 Hz to 40 kHz). Do I need a DMM that 'goes' to at least 40 kHz on ACV to make a useful measurement here?

For instance, my 5½ digit 220,000 count bench DMM claims to have a 3 dB bandwidth of 300 kHz. On the 200 mVAC range it clearly doesn't meet the required ±0.15% accuracy figure, but it's what I've got. (Accuracy is given as %rdg + counts: 20 Hz to 50 Hz => 1.00 + 100, 50 Hz to 10 kHz => 0.35 + 100, 10 kHz to 20 kHz => 0.6 + 200, 20 kHz to 50 kHz => 1.5 + 250, 50 kHz to 100 kHz => 5 + 400.) Do I just need to make the calculations about my DMM's worst case error in each (of its) bands and make sure that my measured value including the error is below the required (specified) level?

Thanks, Brian.


Stephen
 

I’m almost as new as you are to this, and here. But it sounds like the same problem I have with a 465. I have a dead HV Multiplier. Experts here will guide you and tell you more. I hope I’m wrong.


Jake W
 

Hey guys,

I just got a Tektronix 475 from ebay. The fan spins, lights come on, but there’s no trace and no dot when I hit “beam finder”. I measured the power supply test points and got these results:

+5: 4.99v, 48.5 ohm to ground, 0mv ripple voltage
-8: -7.96v, 40.8 ohm, 0mv ripple
+15: 14.98v, 68 ohm, 4mv ripple
+50: 50.00v, 2.78k ohm, 36v* ripple
+50 unregulated: 67v, OL, 31.9v* ripple
+105/160: 139.4v, OL, 13.8v* ripple
+110: 111.1v, OL, 20.9v* ripple

* where I measured high ripple voltages, my multimeter switched back and forth from That voltage to zero in about 1 second intervals. Not sure what that means.

The resistance on the +5, -8, and +15 volt rails seems very low, is that normal? I didn’t see any expected values in the service manual (although I haven’t read too deep).

I also noticed some kind of corrosion around where the giant caps(?) are.

It might be worth noting that the beam finder seemed to work on the ebay listing, but I haven’t been able to make it work.

I’m new here and fairly new to electronics in general so I’d appreciate any help. Thanks!