TDS400 power supply - Page 1
Forum section: electronics / repair

author: james_s
author_rank: Super Contributor
timestamp: March 18, 2017, 11:21:56 pm
content: I picked up a TDS460 with a bad power supply. Is there a schematic available for this? I haven't had any luck finding one yet. At the very least I could use a photo of the bottom of the PCB since mine has experienced a rather spectacular flashover that has vaporized a couple of traces. Also R12 near the chopper transistor is burned badly enough that I can't conclusively read the value.Also there are the typical leaky SMT electrolytics on all the other boards. When I replace these in vintage computers I normally use tantalum chip capacitors instead since they never leak. I suspect these will work fine here because most of them appear to just be power supply bypass caps but I'm wondering if anyone has tried this on one of these scopes. The newer TDS scopes use ceramic chip bypass capacitors.

author: tautech
author_rank: Super Contributor
timestamp: March 18, 2017, 11:26:27 pm
content: What scares me is that hybrid, for your sake I hope it's ok.

author: james_s
author_rank: Super Contributor
timestamp: March 18, 2017, 11:37:02 pm
content: Yeah I'm hoping that's ok. I believe I saw somewhere what's inside it though and it wasn't all that much.Worse case I can buy a few more of these scopes

author: tautech
author_rank: Super Contributor
timestamp: March 18, 2017, 11:39:19 pm
content: What voltages does it supply .....maybe one of the other TDS*** uses the same supply ?

author: james_s
author_rank: Super Contributor
timestamp: March 18, 2017, 11:51:48 pm
content: I'm not sure, I think it's the same PSU that's used in all of the TDS300 and TDS400 series scopes. Apparently the LeCroy 9354 uses an almost identical PSU and I found the schematic for that, but R12 must be different. It says 500 Ohm on the LeCroy schematic but this looks like orange-brown-black, 310 Ohm is not too far out from 500 so maybe it's safe to assume that's what it is.What I'm shocked to discover is that the chopper transistor tests good. I thought sure that was gonna be dead shorted. Makes me think an insect or lump of moist lint got in there and just started burning rather than a catastrophic failure. There were a couple of other dead bugs inside the scope.

author: tautech
author_rank: Super Contributor
timestamp: March 19, 2017, 12:06:22 am
content: Quote from: james_s on March 18, 2017, 11:51:48 pmI had exactly this happen in my main PC PSU. After being turned off for a week while away a/the little bugger absorbed atmospheric moisture that then created a short and blew the PSU when mains was reapplied.Wrote about the whole saga here:https://www.eevblog.com/forum/projects/your-stupidest-mistakes/msg1111707/#msg1111707

author: james_s
author_rank: Super Contributor
timestamp: March 19, 2017, 04:19:12 am
content: Well I cleaned up the carbonized PCB and worked out where the vaporized traces went. Found a shorted diode and mosfet and replaced those. Now I can apply power and nothing blows up however I think that hybrid is zappedFortunately though I found the schematic that someone reverse engineered from onehttps://www.eevblog.com/forum/repair/lecroy-lc534al-repair-attempt/I may try to build a replacement module once I can verify for sure that it's bad. It's a reasonably simple circuit.

author: Fiveten
author_rank: Newbie
timestamp: January 22, 2019, 01:41:32 am
content: Check mr carlsen’s Lab on YouTube. He rebuilt a hybrid for this power supply.It supplies 15v, -15v, -6.3v, 5vI am working on a tds 460 power supply that is not like yours or any other I see on forums. It is the PS2217 / 119-5549-01I have yet to find a schematic for either PS as of yet. Good luck.

author: james_s
author_rank: Super Contributor
timestamp: January 22, 2019, 02:17:20 am
content: Interesting, I'll check it out. I remember one of his videos where he repaired one but I don't think there was anything wrong with the hybrid on that one. I haven't messed with these in a while, I have other scopes so it has been low priority. I would like to get them working some day though, I have two dead ones.