Tektronix 535a & 561b - Help needed for repair.

[blitzaxt]

I bought two Tektronix oscilloscopes at a estate sale. I am starting to get into electronics and wanted to get an oscilloscope to learn with. Since they were selling two for a decent price I decided to buy both. I am lucky to have a very Patient wife.

So on to the sick puppies.

I looked them over quickly for anything that looked burnt/particularly bad and did not find anything. I proceeded to turn them on one at a time.

561b:
I started with the smaller 561b and fiddled with the knobs and got a trace but after a while the trace went away. I did not notice any pops, bangs or magic smoke. There is no evidence of a trace even when turning up the intensity.
I checked the low voltages and -100 was -104, I adjusted that down and the other low voltages seemed to come into spec.
I do not know where to go from here as the troubleshooting is not as clear as in the manual for the 535a.

535a:
Took a look at this guy second. Started out with no trace. After a quick google search I read this article: http://www.lydecker.org/Tektronix_535A.htm he mentioned in the article that the contacts on the tubes may be at fault. I wiggled the tubes a little and I got a trace. YAY!



Then I turned it off and started cleaning the contacts for the tubes with contact cleaner. I got part of the way through - I have cleaned all the contacts in the plugin, the left side of the scope, the door on the right side of the scope and the bottom of the inside of the door on the right side of the scope. Now there is no trace  I am hoping I did not fubar something. I did notice that the trace seems to be above the screen as the up arrow light lights up and i can see a faint, fat vertical line about when I turn up the intensity. The vertical position knob did not affect the position of the line. I do have a second plug-in and it seems to give the same issue.



I followed the troubleshooting steps outlined under 'Troubleshooting the vertical amplifier', 'No Spot or Trace on CRT'. When shorting things as instructed it showed the trace near the center as specified. The manual has this to say about my perdicament:
'If tube replacement does not correct the trouble, then look for open peaking coils, defective resistors and shorted or leaky capacitors.'
I cannot exactly go to my local Walmart and pick up different tubes for it (even if I could I don't think I would buy them there). Is there a good way to test tubes without a tube tester, I do not exactly have one at my disposal.

I am going to bring the manual to work and scan in the Schematics on our big scanner. The manual can be found here: INSERT URL but the schematics are separate making it hard to read.

Some background on me:

I am a computer person by trade, my speciality is Cisco networking. I have not done much in the way of electronics repair except a laptop jack replacement and other small repairs of the like that are obvious. This is not obvious to me. I work on my car when it breaks, I dabble in woodworking, I go to school, I work full time, I have 3 kids and a wife. I must have too much time on my hands . I was put down this whole path in part because of the videos on youtube from EEVBlog, it seems like a great community.

Please be patient with my post as I have less than no idea what I am doing. I will try to improve the post and add more information as I troubleshoot more. Let me know if any more information is needed.

TLDR: I have no idea what I am doing and I could use some help repairing two old Tek scopes.

Edit: Images broke.

[VK5RC]

Hi,  I have just finished restoring  a 545, I have a thread on here about it.  I am not an EE,  from my perspective you seem to be doing ok so far,  I bought a tube tracer,  the uTracer I recall from Northern Europe,  not cheap but it was VERY useful as I had 3 dead tubes.  As tubes are quite high impedance devices,  I thought cleaning important  to avoid dust/cig smoke/moisture completely interfering with the circuits.  I don't know what contact cleaner might do. 
If no other help comes here I would try the yahoo Tek group and also you might have a local antique radio group who might help.
I got all the tubes I needed off eBay without much trouble. 
I would comment I did this as a restoration project rather than getting a useful scope,  if that is your aim,  putting the effort directly to that end may be better,  but a 500 series Tek is a thing of beauty!
Robert

[VK5RC]

PS your images are now working,  is the true trace off screen? ,  the vertical position control (adjust till up and down arrow indicators are equal intensity) apologies if you have done this.

[blitzaxt]

 I forgot to mention that moving the vertical position control either way does nothing.
Thanks for the encouragement! I am a form follows function kinda person so I want it clean but I don't have the patience to paint it.

A bit of an update, I checked my voltages (yeah go figure). All the low votlages were quite happy except +100 is at +124 no adjustment of -150 (without going out of range). It does not go up to this voltage until the time delayed relay kicks over, until then it is at a beautiful +100.

[Cyberdragon]

I just got a 561a which should be very close to your model 561b (except for the calibrator). First, remove both plugins and see if you get a dot. If you do then one of the plugins is throwing the trace off the screen. If not then check the filaments of the CRT and the two hv rectifiers with an ohmmeter (careful though, the filements of the rectifiers are electrically fragile and can burn out easily). Check the intensity pot resistance to make sure it's not open.

[tautech]

There's a good thread about restoration of these old Tek classics, I suggest you place a post there with a link back to this one.
https://www.eevblog.com/forum/testgear/vintage-tek-restoration-pictures-by-martin/

Martin will then hopefully come to your rescue.

[VK5RC]

+1 re Martin. M he breathes Tektronix knowledge! HiHi
Re the 535:I would tend to look at the power supply issues first, in the 545 the - 150v rail sets the voltage regulation control for all the others,  I wouldn't be surprised if the 535 is similar,  there are current limiting resistors in each of the  'low voltage'  rails ie 100v to 500v. (in the 545 they are about 5 or 10 ohms on the bottom of the scope).  The voltage drop across each resistor tells you if they are being loaded down by the scope itself.  The expected voltage drop in the 545 was on one of the psu schematics.
It's also worth   checking the 'low voltage'  filter caps (in the 545 on the top RHS shelf at the back,  in front of the high voltage power supply),  mine were close to a short (about 1k ohm).
Also be careful - lots of dangerous voltages. 

[poot36]

I have no experience with either of these scopes but I have seen in other tube equipment the seleanium rectifier diodes go bad and cause all sorts of problems.  If they are used in the high voltage circuit for driving the anode of the CRT (voltage multiplier) then they can cause a weak or nonexistent trace.  I would check that all the variable resistors are still working properly.  If the wiper contact of one of the pots is not making contact then nothing will work or it will work incorrectly.  Make sure to check the power supply for ripple on the output by setting your meter to AC volts and seeing what you get.  If it is over 1V I would be concerned that the filter caps are bad or your meter is not capable of filtering out the DC component of a signal on the AC range (this usually indicates a very cheap meter).  You can do a quick check on the tubes by seeing if the heater glows on all the tubes and you can check them for major shorts by looking up the diagram of the tube and its pinout and using you meter on ohms mode to go between the heater and the cathode, cathode and the grid, grid to grid (if the tube has more then one grid), and gride to anode.  Also look for the cathode glowing red hot that is a sign of a bad or miss biased tube and that will destroy the tube in a few seconds.  I would change out all the wax, paper, and black tubular caps ( known as black beautys or bumblebees in vintage tv's and radios)  with a modern replacements (any of the poly based caps will do unless someone else can recommend a better replacement) if you want to have this scope be reliable.

[Cyberdragon]

I don't think there are any selenium rectifiers but IDK (in the 561B they will definately be mostly silicon).

It's the anode that's not supposed to glow (or the grids), the cathode always glows. You really should get a proper tube checker, a glowing tube can have no shorts and still be stone cold dead (or have heater to cathode leakage which has to be tested for when the tube is hot).

The caps in these things make other caps look stupid, they are designed to be reliable. All of the non-electrolytic ones will be mylar or ceramic (I think there's even an oil cap in mine) which are perfectly fine. The electrolytics should still be ok but if any get warm or test low then they need to be replaced. Check ripple to see if the caps are low, also switch it to the lowest input voltage with the input set to ground and the line should be perfectly flat if there is low ripple.

[blitzaxt]

I just got a 561a which should be very close to your model 561b (except for the calibrator). First, remove both plugins and see if you get a dot. If you do then one of the plugins is throwing the trace off the screen. If not then check the filaments of the CRT and the two hv rectifiers with an ohmmeter (careful though, the filements of the rectifiers are electrically fragile and can burn out easily). Check the intensity pot resistance to make sure it's not open.

I will give that a try when I get home, thanks for the tip!
By the way if I have to test the HV rectifiers how do I avoid burning out the filaments. I do not want my lack of knowledge to cause more problems.

+1 re Martin. M he breathes Tektronix knowledge! HiHi
Re the 535:I would tend to look at the power supply issues first, in the 545 the - 150v rail sets the voltage regulation control for all the others,  I wouldn't be surprised if the 535 is similar,  there are current limiting resistors in each of the  'low voltage'  rails ie 100v to 500v. (in the 545 they are about 5 or 10 ohms on the bottom of the scope).  The voltage drop across each resistor tells you if they are being loaded down by the scope itself.  The expected voltage drop in the 545 was on one of the psu schematics.
It's also worth   checking the 'low voltage'  filter caps (in the 545 on the top RHS shelf at the back,  in front of the high voltage power supply),  mine were close to a short (about 1k ohm).
Also be careful - lots of dangerous voltages. 

I will take a look, I saw earlier that the +100 rail stays at 100 until the relay kicks over then it shoots up to 124 . I assume this means that something is pulling it high. No other voltages change. According to the manual (4-14) the +100 is regulated by comparing to ground does that mean that ground is messed up? I have no idea how this part of things works. +100 also goes into the plugin.

I have no experience with either of these scopes but I have seen in other tube equipment the seleanium rectifier diodes go bad and cause all sorts of problems.  If they are used in the high voltage circuit for driving the anode of the CRT (voltage multiplier) then they can cause a weak or nonexistent trace.  I would check that all the variable resistors are still working properly.  If the wiper contact of one of the pots is not making contact then nothing will work or it will work incorrectly.  Make sure to check the power supply for ripple on the output by setting your meter to AC volts and seeing what you get.  If it is over 1V I would be concerned that the filter caps are bad or your meter is not capable of filtering out the DC component of a signal on the AC range (this usually indicates a very cheap meter).  You can do a quick check on the tubes by seeing if the heater glows on all the tubes and you can check them for major shorts by looking up the diagram of the tube and its pinout and using you meter on ohms mode to go between the heater and the cathode, cathode and the grid, grid to grid (if the tube has more then one grid), and gride to anode.  Also look for the cathode glowing red hot that is a sign of a bad or miss biased tube and that will destroy the tube in a few seconds.  I would change out all the wax, paper, and black tubular caps ( known as black beautys or bumblebees in vintage tv's and radios)  with a modern replacements (any of the poly based caps will do unless someone else can recommend a better replacement) if you want to have this scope be reliable.

For the 535a I do not think there is a problem with the CRT as shorting the leads as in the troubleshooting steps makes the trace appear. I do not know on the 561B yet but as Cyberdragon stated the 561B does in fact have no tubes in the chassis itself just the plugins.
I will definitely look at the power supply ripple that is something I had not even thought of.
All the heaters glow from what I can see, I will give the ohm meter a try.
The bumblebee caps what do they look like? I only see a ton of resistors, are some of the resistors in fact caps in disguise it would make sense as some of them seem quite large.

I don't think there are any selenium rectifiers but IDK (in the 561B they will definately be mostly silicon).

It's the anode that's not supposed to glow (or the grids), the cathode always glows. You really should get a proper tube checker, a glowing tube can have no shorts and still be stone cold dead (or have heater to cathode leakage which has to be tested for when the tube is hot).

The caps in these things make other caps look stupid, they are designed to be reliable. All of the non-electrolytic ones will be mylar or ceramic (I think there's even an oil cap in mine) which are perfectly fine. The electrolytics should still be ok but if any get warm or test low then they need to be replaced. Check ripple to see if the caps are low, also switch it to the lowest input voltage with the input set to ground and the line should be perfectly flat if there is low ripple.

I get no trace so how would I check for the line ripple or do I misunderstand? I will look for warm caps as I am going through.

Thanks for all the input I will try to do more troubleshooting when I get home tonight. Let me know if there is any more information I can provide.

[PaulAm]

Two other resources that may be of use to you.

The yahoo tekscopes group has a lot of knowledgeable people.  Most of the discussion these days seems to center around the 2200 and 2400 series, but others pop up.  You have to join to participate in the discussions.

The site http://www.antiqueradios.com has a lot of people who know a great deal about vacuum tube equipment.  You would be likely to get a good reception there as well.

I'm not a big fan of vacuum tubes bigger than nuvistors, but those are neat scopes and worth preserving.  They're works of art on the inside.  If you do any repair though, be sure to use solder with a silver content on the ceramic tiepoints.  They used to leave a roll of it in the scope somewhere, but you can find small quantities of 1-2% Ag solder for reasonable prices.  Using ordinary solder can cause the silver plating on the ceramic tiepoint to delaminate.

[Cyberdragon]

Actually, you should be fine to test the filaments. I just checked and they are 1.2V which should be way more than a DMM puts out. (If you have an analog meter, put a red LED across the leads in low ohms mode and it should not light or be very dim. If it's bright you have a problem) Some HV rectifiers have filaments that use 0.6V so those are the fragile ones.

Mine still has the solder inside. (It was last repaired in 1985 so it only needed a bit of adjustment)

[VK5RC]

I have had a quick look at the manual,  the 535,  I think,  has exactly the same low voltage power supply as the 545,  I am pretty sure no low voltages should appear until after the delay relay clicks in,  The only voltages prior should be the filament supplies.
The - 150v supply is regulated off a tube type voltage regulator and all the other supplies refer to the - 150.  Voltage appearing early at the 100v etc points to trouble in the relay and other power supply components.  Have you given the relay contacts a clean?   I used a heavy 'bond'  type paper soaked in contact cleaner drawn through with just a little pressure on the contacts.

[blitzaxt]

So an update:
535a
I went for a bit of a walk up a garden path looking at some resistor values trying to locate the problem with the +100 volt running at +125 and I now know that the resistors around the regulating tube (V664) for +100 seem happy.

I have had a quick look at the manual,  the 535,  I think,  has exactly the same low voltage power supply as the 545,  I am pretty sure no low voltages should appear until after the delay relay clicks in,  The only voltages prior should be the filament supplies.
The - 150v supply is regulated off a tube type voltage regulator and all the other supplies refer to the - 150.  Voltage appearing early at the 100v etc points to trouble in the relay and other power supply components.  Have you given the relay contacts a clean?   I used a heavy 'bond'  type paper soaked in contact cleaner drawn through with just a little pressure on the contacts.

I cleaned it again, I have not tested it yet I left it to dry.

561b
Minor success - I found a bad 150ma fuse on the scope itself. I am hoping that it died due to age and not another component that is unhappy. The Fuse is F9 and it goes to the positive of the high voltage oscillator. Thinking about it now one of the connections had fallen off of the CRT and that could have caused a short blowing the fuse. The stupid $*&^ fuse is almost impossible to find for a reasonable price 150ma 30mm x 6mm, the shorter one is cheaper but I am not keen on rigging something like that...

Actually, you should be fine to test the filaments. I just checked and they are 1.2V which should be way more than a DMM puts out. (If you have an analog meter, put a red LED across the leads in low ohms mode and it should not light or be very dim. If it's bright you have a problem) Some HV rectifiers have filaments that use 0.6V so those are the fragile ones.

Mine still has the solder inside. (It was last repaired in 1985 so it only needed a bit of adjustment)

I am hoping everything is just happy after I put in the fuse... Yeah like that will happen.   

Two other resources that may be of use to you.

The yahoo tekscopes group has a lot of knowledgeable people.  Most of the discussion these days seems to center around the 2200 and 2400 series, but others pop up.  You have to join to participate in the discussions.

The site http://www.antiqueradios.com has a lot of people who know a great deal about vacuum tube equipment.  You would be likely to get a good reception there as well.

I'm not a big fan of vacuum tubes bigger than nuvistors, but those are neat scopes and worth preserving.  They're works of art on the inside.  If you do any repair though, be sure to use solder with a silver content on the ceramic tiepoints.  They used to leave a roll of it in the scope somewhere, but you can find small quantities of 1-2% Ag solder for reasonable prices.  Using ordinary solder can cause the silver plating on the ceramic tiepoint to delaminate.

I joined the Yahoo group and will post there as well thanks for the tip. I will look into antiqueradios as well. Thanks!

By the way I am in Akron, Ohio if anyone knows of any good old timey tube shops or the such in the area let me know.

[David Hess]

561b:
I started with the smaller 561b and fiddled with the knobs and got a trace but after a while the trace went away. I did not notice any pops, bangs or magic smoke. There is no evidence of a trace even when turning up the intensity.
I checked the low voltages and -100 was -104, I adjusted that down and the other low voltages seemed to come into spec.
I do not know where to go from here as the troubleshooting is not as clear as in the manual for the 535a.

See if the trace reappears after the 561B cools down and then vanishes again after it warms up.  If so, the high voltage transformer may be bad.  Inspect it to see if it has brown epoxy.  The brown epoxy is known to absorb moisture increasing loss and causing the high voltage oscillator to fail.  Tektronix later used a different epoxy which was black and did not have this problem.

These can be useful oscilloscopes even today but I think you may be in over your head effectively having to refurbish them.  Given their age and operation condition, I would systematically check them over starting with the low voltage power supplies.

[blitzaxt]

See if the trace reappears after the 561B cools down and then vanishes again after it warms up.  If so, the high voltage transformer may be bad.  Inspect it to see if it has brown epoxy.  The brown epoxy is known to absorb moisture increasing loss and causing the high voltage oscillator to fail.  Tektronix later used a different epoxy which was black and did not have this problem.

These can be useful oscilloscopes even today but I think you may be in over your head effectively having to refurbish them.  Given their age and operation condition, I would systematically check them over starting with the low voltage power supplies.

The trace has not appeared since on the 561b.
I am starting to wonder if I am a bit in over my head, I will start with the low voltage power supplies and go from there. I am hoping that since the 561b has nice and happy voltages that replacing the fuse that I assume blew from one of the connections from the CRT coming loose (I think it was one of the vertical lines) I will be in business.

[tautech]

I am starting to wonder if I am a bit in over my head, I will start with the low voltage power supplies and go from there.

You'll be OK, there's plenty keeping an eye on you  , make good notes and share your developments all the way. Threads like these are great records for those that find them with similar problems in the future.
If you get stumped, proceed with something else that needs doing, cleaning, physical repairs etc. until someone comes to your aid.
Proceed like a detective....expect anything and everything, isolate and eliminate areas one at a time, again make notes, take pics and so on.
Share as much as you feel happy to, we'll get you through.

[Cyberdragon]

Don't worry buddy, the glowing glass side is warn and cozy.

Wait  you said a fuse blew in the HV circuit right? (561a doea not have this, so I don't know where in the circuit this would be) If wire came off that looks like a vertical deflector wire (was it from the sides or the socket?) then it could not have blown the HV fuse, the deflector plates go straight to the plugins. Some other component must be shorted in the HV supply.

[David Hess]

The trace has not appeared since on the 561b.

I am starting to wonder if I am a bit in over my head, I will start with the low voltage power supplies and go from there. I am hoping that since the 561b has nice and happy voltages that replacing the fuse that I assume blew from one of the connections from the CRT coming loose (I think it was one of the vertical lines) I will be in business.

Touching one of the deflection leads to ground is usually fatal to the CRT amplifier but as Cyberdragon mentioned, the 561B is different with the deflection signals coming directly from the plug-ins so I am not sure about it.  We need to know what plug-ins are installed.

[blitzaxt]

I am starting to wonder if I am a bit in over my head, I will start with the low voltage power supplies and go from there.

You'll be OK, there's plenty keeping an eye on you  , make good notes and share your developments all the way. Threads like these are great records for those that find them with similar problems in the future.

Thanks for the encouragement and direction!

Don't worry buddy, the glowing glass side is warn and cozy.

Wait  you said a fuse blew in the HV circuit right? (561a doea not have this, so I don't know where in the circuit this would be) If wire came off that looks like a vertical deflector wire (was it from the sides or the socket?) then it could not have blown the HV fuse, the deflector plates go straight to the plugins. Some other component must be shorted in the HV supply.

I will need that this winter.   

So i did something kinda dangerous. I did not want to wait for my 7 dollar 5 pack of fuses to come in on the 1st of Nov. and I bypassed the fuse.  I used my digital multimeter in the Miliamp range and kept a close eye on the miliamprage. Looking at even fast blow fuses take a second to blow. I had my finger on the off switch and gave it a shot.


 

I think it was a ID-10-T error, I may have crossed the streams when I was messing with it. I have no real idea but I do not think there is an issue with the HV circuit as it is going to the HV oscillator not from. Again I have no idea.

[David Hess]

> Photograph of working 561B with 3A6 and 3B3 Plug-ins

I think it was a ID-10-T error, I may have crossed the streams when I was messing with it. I have no real idea but I do not think there is an issue with the HV circuit as it is going to the HV oscillator not from. Again I have no idea.

There is nothing wrong with leaving it running for a couple hours but I would keep it  under supervision just in case.

The 561B with those plug-ins has a 10 MHz bandwidth (its maximum), 10mV/div sensitivity, and dual delayed sweep (magnification of part of a waveform) to 500ns/div.

[VK5RC]

Looking good!
Only those who haven't tried haven't made mistakes.

[poot36]

Here is a link to a video showing tube testing and component replacement on a old TV:    At the 32:07 mark you can see what I think is the cathode on the video amp tube glowing orange hot.

[Martin.M]

what`s going on withe both scopes actually?
may be I can help here a little

Martin