Tektronix 535A Suddenly Multiple Problems - Page 1
Forum section: electronics / repair

author: Positron 25
author_rank: Newbie
timestamp: November 02, 2020, 04:39:00 am
content: I have had a 535A scope for many years and love it. Unfortunately, suddenly had a problem, then multiple problems. The ceramic connections of wires and parts, I shall call pins.1. Initial problem was vertical, both A and B suddenly went off screen. I checked the supply voltages at the labeled check points on top of the scope and the -150 and +225 voltages were way off. Replaced tubes, cleaned tube pins but did not help.2. Spent some 30 hours checking passive parts, did not find any problems. After an arc from a 500 volt supply pin to a grounded pin (on the ceramic/arm that swings out), I realized the problem could be leakage or worse between pins. So I cleaned (sandpaper and no residue spray) between pins throughout the scope, and the vertical started working properly. All the voltages measured fine, within 1-1 3/4% at the test points on top of the scope.3. Checked the scope and Alternate and Chop do not work. Just a single line. The vertical position works fine, respectively.4. I checked voltages at the CA plugin socket, no CA plugged in, and these were the voltages.Pin 9 -50 voltsPin 10 +131Pin 11 +119Pin 12 120With the CA plug in installed.Pin 9 -49 voltsPin 10 +72Pin 11 + 88Pin 12 + 88The vertical measurements seem accurate when using the Amplitude Generator Cal out.When I set Horizontal Display to B, Channels A and B still work, but the horizontal line is only about 1/2 the width across the screen as when Horizontal Display is set to A. Alternate and Chop still do not work.I checked and plate of V245 has a pulse. However, the screen pin 6 does not. V154 has nothing. I did spray clean the switches, but the spray leaves no residue.I can use the scope in channel A or B, but sometimes it is nice to use Alternate.By the way, I cannot find 100 ohm resistors R 603, 605, 607, 609. So difficult to find the parts.I am an analog audio design expert, but not very good with scopes. What I am wondering is if the problems could point to one particular area or part, or whether there are multiple problems. Is this just a coincidence of multiple problems?Thanks for any help and time/efforts.pos 25

author: Tom45
author_rank: Frequent Contributor
timestamp: November 02, 2020, 05:10:20 am
content: Another great source of all things Tektronix is the TekScope forum at:https://groups.io/g/TekScopesA wealth of knowledge there about Tektronix scopes.

author: med6753
author_rank: Super Contributor
timestamp: November 02, 2020, 09:31:55 am
content: There is a huge discrepancy between what you state the voltages are on those pins on the plug-in connector and what the schematic indicates. See partial Type 535A Vertical Amplifier.Pins 9, 10, 11, and 12 should be within a few volts as indicated allowing for a slight drop through the resistors. Your measurements are no where near that. And they won't change much regardless of a plug-in installed or not because the PSU voltages are regulated. I suggest you go back and make sure you are on the correct pins. You have no hope of fixing the CA plug-in until this is resolved.You stated...."When I set Horizontal Display to B, Channels A and B still work, but the horizontal line is only about 1/2 the width across the screen as when Horizontal Display is set to A. Alternate and Chop still do not work. "Sounds like you might have it in delayed sweep which intensifies part of the beam. Turn up the intensity and the other half of the trace will appear.The component side of the CA plug-in can be accessed for troubleshooting by removing the CRT side of the 535A cover but it is awkward. Best to have a plug-in extender. They occasionally show up on Ebay but tend to be expensive since they are rare and in high demand.Hope this helps.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 02, 2020, 10:06:53 am
content: Can I make a suggestion?The 535A is a very old device, it may be collectible, but no more valid for regular and professional use.Multiple failures may be due to widespread wear and tear on components that may have reached their end of life.It would be time, it seems to me, to think about replacing it with a more modern analog osciloscope.Personally, I would recommend a Tektronix 465B, preferably in a very good shape.

author: med6753
author_rank: Super Contributor
timestamp: November 02, 2020, 11:19:44 am
content: My 535A has been restored (by me) and gets regular use and within it's limits I would stack it up against any other analog scope for utility and usefulness.A 465B in "good shape" would mean that the vast majority, if not all, of the beaded tantalum capacitors were replaced or else you'll experience unexpected release of magic smoke. Their attenuator switch decks are also a sore spot.A better upgrade would be a 2465....non suffix. The A & B versions have their issues of dead batteries in Dallas chips and on the B the A5 board getting destroyed by leaking tantalums. The 2465 has none of these issues and as long as the PSU has been re-capped it is a solid performer.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 02, 2020, 12:35:14 pm
content: I have a 465B with all of its original tantalum capacitors and as far as I know these capacitors do not used to releasing magic smoke.You shouldn't make generalizations or be paranoid.On the other hand, buying a 2465 is a big mistake .... as it is usually a mistake to buy analog oscilloscopes with read outs and cursors.If you want sophistication just buy a current DSO, they are much more powerful and reliable than that old tektronix 2465 oscilloscope.If you buy an analog oscilloscope, choose a simple model like the 465B, if not, buy a new DSO.NB: I prefer the 465B over the 2235 because it is of higher quality than the 2235 and is more reliable.

author: med6753
author_rank: Super Contributor
timestamp: November 02, 2020, 01:05:46 pm
content: Quote from: akimpowerscr on November 02, 2020, 12:35:14 pmGeneralizations and being paranoid? No pal.....real world experience. I have two 465B's, one 475A, and a parts unit 465 and every one of them has had tantalum issues. And others on the blog have had similar experiences. If yours hasn't, great. But one day, it will.And as far as a 2465. I was merely giving the Op alternatives if he wishes to remain in the analog realm. Of course a DSO is a viable alternative. It's his choice. You don't have to like it and frankly I don't care.

author: akimpowerscr
author_rank: Regular Contributor
timestamp: November 02, 2020, 01:47:09 pm
content: 2 or 3 units 465B are statistically meaningless compared to the thousands of units still in service that have not had problems with their tantalum capacitors.These 465B oscilloscopes are generally around forty years old and everything obviously depends on the number of hours of operation and the ambient conditions, which is why I specified in good shape.That a tantalum capacitor can become defective is one of the risks that we have with any device 40 years old and which already has tens of thousends hours of operation.But this failure is not frequent, nor difficult to diagnose and to repair.A failure every 5 years, this does not require the replacement of all tantalum capacitors ...

author: Tom45
author_rank: Frequent Contributor
timestamp: November 02, 2020, 03:06:48 pm
content: Quote from: med6753 on November 02, 2020, 11:19:44 amI have a 2465 and agree that it is a great scope without the dead batteries problem. The one weak point of the 2465 is the fan motor. Its bearings eventually wear out and get quite noisy. There are no direct replacements any more, so the options are to rebuild the motor or cobble together something using a modern computer fan.

author: Positron 25
author_rank: Newbie
timestamp: November 02, 2020, 03:22:54 pm
content: Quote from: Tom45 on November 02, 2020, 05:10:20 amThank You Tom. Much appreciated.cheerspos25

author: Positron 25
author_rank: Newbie
timestamp: November 02, 2020, 03:28:12 pm
content: Quote from: med6753 on November 02, 2020, 09:31:55 amThank You Med. I now see that the plug is numbered different than an integrated chip. Yes, the voltages are all ok.B variable was not in the calibrated setting, now is, and the horizontal sweep in B is now ok in length.So it looks like all is ok except for the Alternate and Chopped settings. That certainly simplifies things.As of now I am not getting any pulse at the grid of V154. Will again examine that when I get a chance.Helps by any is still certainly appreciated.Cheers and thank you for your assistance Med.pos25