Tektronics TDS744a repair (with pics) - Page 1
Forum section: electronics / repair

author: mlefe
author_rank: Regular Contributor
timestamp: December 22, 2017, 04:35:32 pm
content: Hi guys, I wanted to share with you my latest "repair".I've bought a TDS744a oscilloscope from ebay that kept repeating the pattern of turning on, and then off in a quick cycle (you could hear the fan and see briefly the leds turning on right before it turned off)Suspecting the power supply I went directly to it and sure enough, lots of damage around 3 caps (see attached pictures)Remebering Dave's video on the shorted cap from a portable power supply, I kept removing the PCB until there was no more carbonisation (keep in mind that I'm learning electronics relying on what I learn from the internet, I have no formal studies on it, so my "knowledge" is 100% empirical)I then replaced those caps and all the other ones from the power supply with the best brands I could find (I'm argentinian but living in Colombia, not easy to get parts around here) and rebuild the traces with wires and what do you know? It works!I still feel that the repair was a bit ugly in terms of the wiring and the scrapping of the PCB but in the end, it's a nice addition to my hobbiest benchThe next step should be to upgrade it to a tds784 by removing the caps and resistor on the acquisition board, but I'll wait until I really need it (or have probs that could benefit from that...)Sent from my Galaxy S8

author: deepskyridge
author_rank: Regular Contributor
timestamp: December 22, 2017, 06:01:45 pm
content: I have the same model scope with a power supply that failed in exactly the same way.What did you fill the hole with.Gary

author: mlefe
author_rank: Regular Contributor
timestamp: December 22, 2017, 06:13:05 pm
content: Quote from: deepskyridge on December 22, 2017, 06:01:45 pmHi Gary, I didn't filled it in, I left it wide open... as I said, a bit ugly Martin.-Sent from my Galaxy S8

author: shakalnokturn
author_rank: Super Contributor
timestamp: December 22, 2017, 08:50:32 pm
content: Who needs a PCB for anything with less than 4 layers anyway?

author: mlefe
author_rank: Regular Contributor
timestamp: December 22, 2017, 09:25:04 pm
content: Quote from: shakalnokturn on December 22, 2017, 08:50:32 pmSent from my Galaxy S8

author: andy2000
author_rank: Frequent Contributor
timestamp: December 22, 2017, 09:32:55 pm
content: Electrolyte from leaking caps caused the board to fail like that. I had to repair similar damage on a 744A a few years ago. There were several other leaking caps in the same power supply, and also on the monitor board. I had a different scope where a carbon track formed under a cap on the monitor board and caused the scope to shut down.

author: mlefe
author_rank: Regular Contributor
timestamp: December 22, 2017, 09:36:20 pm
content: Quote from: andy2000 on December 22, 2017, 09:32:55 pmThat was exactly the case! Just in case I've replaced all of them... I didn't want more of thatSent from my Galaxy S8

author: cncjerry
author_rank: Unknown
timestamp: December 22, 2017, 10:33:56 pm
content: you now have a great scope. What did you pay for it? I bought mine for $400 with 5 or 6 probes. I actually bought it for the probes and the guy threw in the scope. I upgraded mine to the 784 and it is one of my prized possessions. I love that scope. I know if I say this, someone will jump all over me, but I think the colors in a properly working 744 are just beautiful, one of the best looking but a lot of people complain about the shutter. One of these days I have to open mine and check the calibration oscillator as it seems really noisy but it could be just the wide bandwidth of the scope.Best of luck with it and I hope it stays reliable. Mine has been for years.Jerry

author: mlefe
author_rank: Regular Contributor
timestamp: December 22, 2017, 10:38:48 pm
content: Quote from: cncjerry on December 22, 2017, 10:33:56 pmI've paid 270+shipping (quite expensive to get to Colombia, though) but it had no probes...I've bought a used 500MHz (p6139a) but didn't arrive yet: do you have active probes on yours?Is what you mention the cause for some horizontal flickering I can see in the screen from time to time?Sent from my Galaxy S8

author: cncjerry
author_rank: Unknown
timestamp: December 23, 2017, 11:11:28 pm
content: The scope has a wide bandwidth so the horizontal flickering could be anything. The shutter is related to how the display draws the colors.http://w140.com/Oscilloscopes_in_color_tek_5116.pdfSome people complain of headaches due to the shutter flicker, I, who is a serious migraine sufferer, have never had a problem with the shutter. I just find the colors to be really deep, sort of like Elvis on velvet, almost 3D. Granted, I fell in love with the scope two years ago and there are much better technologies. I have a 3054C that I got for a deal but if I have the room I drag out the 784C.I have two active probes (P6205) and 6 or 8 of the typical tek probes as well as a dozen or so of the cheap asian versions. I use the hp probes that come with the 54003 type modules. I find they are the best deals out there and my 5371a counter uses the modules and most tek scops can support the bare probes. The probes generally come with all the parts, adapters and connectors and since they are so limited in use, you find them cheap.

author: mlefe
author_rank: Regular Contributor
timestamp: December 23, 2017, 11:52:39 pm
content: Quote from: cncjerry on December 23, 2017, 11:11:28 pmGreat info, thanks!