TDS 540A tektronix oscilloscope capacitors list? - Page 1
Forum section: electronics / repair

author: coppercone2
author_rank: Super Contributor
timestamp: October 04, 2023, 05:01:55 am
content: I had this unit that was powered down for a while. Now it shows a failure on Attn/Acq interface. I got signals that kinda drift about. I thought it might be the capacitors. I heard there is alot.Does anyone have a list of parts that would work so I can buy em and take some time to replace it without actually determining all the parts to buy?an its a 1992damn ok I found some pdf on the tek wiki, its 33uf an 10uf and their like 5mm.Problem is they look fine. Ugh but it fits the bill for the symptoms.fuckin cant catch a break with this shit lol

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 04, 2023, 06:00:48 am
content: Also, replace the 4x 1000pf or 2200pf 10mm pitch Rifa caps (you'll have to double check exact values), and also C17 (47uF, 80VLOW-ESR electrolytic, feel free to increase voltage rating a bit) if present in in your revision of the PSU too while you are at it.Rifas are self explanatory,. The other cap is for standby power, if it goes high-ESR, it takes out some TVS diodes and a transistor that kills your standby power so the scope won't turn on.It 's getting old, it will be getting a higher ESR now....

author: coppercone2
author_rank: Super Contributor
timestamp: October 04, 2023, 06:18:12 am
content: do you think its plausible that this is the cause of the ATTN ACQ failure?Its only one line that is failing in the test.It was working OK before for a very complicated test setup with 4 channels in ultrasonic band, but there was like jitter and noise that I was not sure where it was coming from. I was not sure if it was my test setup. I am thinking now maybe my test setup was fine and the scope was actually not fine. I gave up on the scope for that experiment and just used frequency and like filters.My rigol1052e also has some kind of keypad problems. I have just been jabbing the keys with a butter knife. God damn oscilloscopes piss me off. The other side of things seems to be working a lot more reliably (frequency equipment).fuck the god damn time domain its nothing but problems

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 04, 2023, 05:32:08 pm
content: These early revision scopes are known for their leaky caps (I just fixed a 'non-letter' model the other week actually, and I had to make a new VCO board too due to corrosion, it's the little tiny board hanging off the ACQ board).It had weird errors and it all came up perfect with the new caps.I usually remove all the old caps by giving them a wiggle until they snap off, then clean up the pads with a solder sucker,lotsof flux, isopropyl alcohol and patience.Then I throw the boards as they are through the dishwasher to clean off the capacitor drippings etc, and then once they have perfectly dried after a couple days and a hairdryer, I finally solder in all the new caps.If you need a replacement VCO board due to corrosion damage, I can send you a spare for the cost of a letter from Japan (won't cost much).Here's a link to the video.of the repair:https://youtu.be/3LS_Xg1ysXk

author: coppercone2
author_rank: Super Contributor
timestamp: October 04, 2023, 11:00:48 pm
content: oh damn I was hoping the cap come off with hot tweezersI wonder if that electrolyte shows up on UV or somethingdaunting repairlol, ended up using the 1660 logic analyser scope as a backup. At least that one works. Cool 50 ohm input too. but having the 4 channel one broken really feels like a kick in the ballsI don't see anything that looks as bad as that there. Infact I don't see any corrosion but I only took a few minutes to look. like the VCO board in that video looks like it got trashed by xenos lolI don't like the texture of the PCB that tektronix made, it looks IMO damaged in the natural state from the surface finish.

author: coppercone2
author_rank: Super Contributor
timestamp: October 04, 2023, 11:20:34 pm
content: ah ok when I look at it very closely it looks like some stuff has dust on it but under the dust there might be corrosion.I guess the dust resisted the compressed air because it got glued by electrolyte maybe. so its plausible. I found a blackened leg on one of the chips too.But I think the VCO board looks OK.alright I guess i got a plan I will order the parts and see where i end up. Looks like I need to send in a few platoons of capacitors to stabilize the situation.Do you use simple green? Or a more advanced detergent in the dish washer?

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 05, 2023, 04:49:02 am
content: The SMD caps come off with a bit of a wiggle, it's really easy. No need for heat until you clean the old solder off the pads.You'll soon see where the leakage is under the caps, if it's hard to find with a look at the intact board, you may be lucky with no real damage done yet.For the dishwasher, I just use standard 'Finish' brand powder, or your local equivalent.Nothing special about it at all.That rough surface is a bit of a pain to clean, but with the dishwasher, well, it's a robot's job.

author: Mgelderland
author_rank: Newbie
timestamp: October 23, 2024, 08:06:53 pm
content: @terra do you remove the Dallas chips when jou put them in a dishwasher?

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 23, 2024, 10:30:49 pm
content: Nope, I leave them in. I do put some kapton tape on the top of the DIP switch though. Not sure if it's needed, but makes me feel better.