Dodgy Repair found in HP6012A Power Supply - Page 1
Forum section: electronics / repair

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 01, 2016, 08:58:43 pm
content: Hi group,I have to share this with the group. This is the weirdest thing I have seen in 40 years of messing with electronics.This is a picture of one of the main switching transistors, MOSFET, in a HP6012A 1kW 50V 60A Power supply.The transistor has been cut open, probably inspected, then carefully soldered shut !!!Regards,Jay_Diddy_B

author: bitseeker
author_rank: Super Contributor
timestamp: September 01, 2016, 09:05:31 pm
content: I wonder what's inside.

author: VK5RC
author_rank: Unknown
timestamp: September 01, 2016, 09:27:21 pm
content: That is weird! I am fascinated as to why you would do that.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 01, 2016, 09:44:06 pm
content: Hi,That MOSFET is still works. I put it on my Tek 571 Curve tracer:It is the same as another one.Regards,Jay_Diddy_B

author: 128er
author_rank: Regular Contributor
timestamp: September 01, 2016, 09:58:01 pm
content: Maybe someone cut it open and hacked a comparable MOSFET inside it? Maybe a TO-220 or DPAK? Why someone should do that? No idea.Edit: Or someone repaired a bondwire inside?

author: jeroen79
author_rank: Frequent Contributor
timestamp: September 01, 2016, 10:56:24 pm
content: Quote from: bitseeker on September 01, 2016, 09:05:31 pmOnly way to know is to open it again.

author: bitseeker
author_rank: Super Contributor
timestamp: September 01, 2016, 11:37:51 pm
content: Quote from: 128er on September 01, 2016, 09:58:01 pmI was thinking the same. Although, if they were doing so to try to preserve the look of the original, they should've at least filed down the solder blobs.QuoteThat sounds plausible.

author: bitseeker
author_rank: Super Contributor
timestamp: September 01, 2016, 11:39:45 pm
content: Quote from: jeroen79 on September 01, 2016, 10:56:24 pmOK, Jay, time for a transistor teardown?

author: tautech
author_rank: Super Contributor
timestamp: September 01, 2016, 11:46:11 pm
content: Quote from: 128er on September 01, 2016, 09:58:01 pmMy guess is this ^^^^

author: lowimpedance
author_rank: Super Contributor
timestamp: September 01, 2016, 11:48:08 pm
content: Quote from: 128er on September 01, 2016, 09:58:01 pmMy first reaction to the pic was of course, but hacking in a comparable device sounded the most plausible to preserve the 'footprint'.As for bond wires how do you re-attach those without the right gear ??.Quote from: bitseeker on September 01, 2016, 11:39:45 pmNow everyone is waiting to see whats under the 'hat' !.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 02, 2016, 12:36:22 am
content: Hi group,I am reluctant to unsolder the lid. Electrically it is the same as unopened transistor.It is the craziest thing I have seen repairing stuff.I believe that the transistor is equivalent to an IRF450.Regards,Jay_Diddy_B

author: bitseeker
author_rank: Super Contributor
timestamp: September 02, 2016, 04:27:40 am
content: The primary reason for opening it is to determine what's been done and what impact that may have on the operation of the power supply. How much power is that one switching?

author: VK5RC
author_rank: Unknown
timestamp: September 02, 2016, 10:07:34 am
content: Why bother to repair something that hard a way! Unfortunately whilst I would love to see what is inside, IF it is working properly (worth a bit of testing and thermal check out) I would leave it alone myself! (Lazy bugger I am)

author: voltz
author_rank: Frequent Contributor
timestamp: September 02, 2016, 11:41:25 am
content: Hmm, my advice, replace the part anyway with a new one (if available).. Then open the thing and see whats inside.If you dont, then who knows how it could fail in the future... Do a proper job, this obviously isn't.

author: Gyro
author_rank: Super Contributor
timestamp: September 02, 2016, 11:56:35 am
content: I very much doubt that you would manage to squeeze much of a package under that lid, certainly not something the size of an IRF[edit:P]450 (unless you sawed that down too!).My bet would be inspection (but why not remove it and test it?) or more likely bond wire. Certainly a desperate step anyway.The soldering looks a bit blobby so I doubt if there's a hermetic seal at the moment. That could further affect reliability.

author: Blastcap
author_rank: Regular Contributor
timestamp: September 02, 2016, 12:31:25 pm
content: Come on, we wanna see!

author: TerraHertz
author_rank: Super Contributor
timestamp: September 04, 2016, 10:36:39 pm
content: That's where they hid the jewels.Or a small treasure map?Come on, open it up. And this time when you re-close it afterwards, put in a zipper.How much do those cost anyway?

author: wraper
author_rank: Unknown
timestamp: September 04, 2016, 10:42:08 pm
content: Strongly advise to replace the part as it is not hermetic anymore and you cannot trust it.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 04, 2016, 11:05:38 pm
content: FWIW, the TO-3P package is mechanically compatible with the old TO-3 (now TO-204AA) package. Fairchild FQA13N50CF should be functionally compatible.The date code on that part says it was made in the 22nd week of 1984, so it's obviously lasted quite a while, but I would replace it anyway. Besides, how can you resist peeking inside to see what - if anything - was done?!?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 05, 2016, 12:13:18 am
content: Hi group,The part has been replaced with a metal can IRF450.I have been saving these parts for 30 years !!I believe that this was state of the art when the HP6012A was introduced.The HP6012A is covered in this issue of the HP Journal:http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1981-08.pdfRegards,Jay_Diddy_B

author: Tomorokoshi
author_rank: Super Contributor
timestamp: September 05, 2016, 02:14:52 am
content: It's simply an extreme version of "Don't turn it on, take it apart!"

author: bitseeker
author_rank: Super Contributor
timestamp: September 05, 2016, 03:41:09 am
content: Thanks for the journal link, Jay. I thought that model sounded familiar. I almost bought one locally when I saw it on Craigslist. Of course, since I didn't jump on it, it was gone the next time I looked.30-year stash of transistors, eh? Nice.

author: Kjelt
author_rank: Super Contributor
timestamp: September 05, 2016, 07:47:34 am
content: Quote from: Jay_Diddy_B on September 05, 2016, 12:13:18 amGreatwhen is the grand opening of the compromised device in the opening post?That is going to be the best suspense tv/youtube video since the 1986 unlocking of Al Capones Vault by Geraldo Rivera

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 05, 2016, 11:13:11 am
content: Hi group,Imightopen it to celebrate the first shipment of theBatteriserBatteroo...In the meantime, I put the part on my Tektronix 476 Curve tracer:The curve tracer indicates an RDSon of 0.32 Ohms at 1AHere is a picture of a IR IRF450 under the same conditions:It gives identical readings confirming my suspicion that the 1855-0473 is or is equivalent to the IRF450.Regards,Jay_Diddy_B

author: setq
author_rank: Frequent Contributor
timestamp: September 05, 2016, 11:15:53 am
content: This looks like the sort of repair my father would have done. TO3 corroded? File off the rusty bits and fill the holes with solder!

author: Blastcap
author_rank: Regular Contributor
timestamp: September 05, 2016, 03:13:23 pm
content: Quote from: setq on September 05, 2016, 11:15:53 amIf it works on cars, why not on electronics?

author: Fraser
author_rank: Super Contributor
timestamp: September 05, 2016, 03:29:25 pm
content: I have seen this done once before when a TO3 transistor could not easily be removed due to it being riveted into a closed chassis. Someone elected to trepan the TO3 to get the lid off, and then fitted a TO220 to the internal connections. In that case the TO3 lid was not refitted so it was obvious what had been done. The TO3 became just a surface mount 'PCB' for the TO220 transistor and its heatsink. This is not an approach that I subscribe to, except in an emergency, but it was in Australia and such unorthodox repairs were commonly known as 'Bush Engineering'Fraser

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 05, 2016, 04:52:50 pm
content: Hi,The MOSFET has a drain connection. May be they called a plumber to fix it ??Regards,Jay_Diddy_B

author: Len
author_rank: Frequent Contributor
timestamp: September 05, 2016, 05:27:36 pm
content: Quote from: Fraser on September 05, 2016, 03:29:25 pm"She'll be roit, mate!" (I've been watching EEVBlog so long, I'm almost bilingual.)Jay_Diddy_B, please open it up and end the suspense!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 05, 2016, 08:30:27 pm
content: Hi group,The can has been un-soldered. Here is the picture:As I suspected, a good silicon die.I opened another IR 1855-0473 and it looks identical:So there was no tampering inside the package.Here is a photograph of the Motorola version of the 1855-0473, a damaged one:Notice how the die is mounted on an angle. This is to get the center of the die closer to the center of the package.Regards,Jay_Diddy_B

author: setq
author_rank: Frequent Contributor
timestamp: September 05, 2016, 08:33:02 pm
content: I can only conclude the previous owner was nuts

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 05, 2016, 08:37:20 pm
content: Quote from: setq on September 05, 2016, 08:33:02 pmIf he was rich, he could have been eccentric.Regards,Jay_Diddy_B

author: TheSteve
author_rank: Unknown
timestamp: September 05, 2016, 08:52:48 pm
content: Maybe Dave used to own it and decided instead of turning it on, he would take it apart.

author: voltz
author_rank: Frequent Contributor
timestamp: September 05, 2016, 09:12:29 pm
content: Glad you replaced it.. Even if the device was working, you've done the right thing by replacing it with a new one.conclusion: maybe the device was opened by someone who just wanted to see what it looked like inside. Thats all.

author: deepskyridge
author_rank: Regular Contributor
timestamp: September 05, 2016, 09:37:22 pm
content: Transistor Stuffing.Gary

author: lowimpedance
author_rank: Super Contributor
timestamp: September 06, 2016, 12:11:52 am
content: Quote from: TheSteve on September 05, 2016, 08:52:48 pmI think your right !.Don't turn it on.......CUT it aparrrrt...Obviously who ever did this takes curiosity to the extreme .

author: bitseeker
author_rank: Super Contributor
timestamp: September 06, 2016, 12:41:47 am
content: Fascinating. Thanks for the show-n-tell, Jay!

author: Kjelt
author_rank: Super Contributor
timestamp: September 06, 2016, 12:21:20 pm
content: Normally the NSA does a better job hiding its bugs

author: VK5RC
author_rank: Unknown
timestamp: September 06, 2016, 12:47:34 pm
content: Wasn't just cut apart looked like they had used a can opener or maybe his teeth.

author: setq
author_rank: Frequent Contributor
timestamp: September 06, 2016, 12:53:55 pm
content: Quote from: VK5RC on September 06, 2016, 12:47:34 pmHaha.Hold my beer....https://youtu.be/tmnFyiPmkNM?t=738... but TO3's...

author: setq
author_rank: Frequent Contributor
timestamp: September 06, 2016, 11:09:09 pm
content: Actually I think I've worked out why this was done. He was clearly looking for Transistor Man!