hp 16500A repair - Page 1
Forum section: electronics / repair

author: electrogeek
author_rank: Contributor
timestamp: November 28, 2015, 05:34:47 am
content: HiI'm new here, but been reading a while, however I have come up against a brick wall trying to find a little detail.I purchased a dead hp 16500A. on closer inspection (Quite a lot closer) I found someone had dropped a screw into the power supply, which had welded itself to the pcb, and caused what i believe are the choppers for the switching converter (a grid of power mosfets, or perhaps an h-bridge, I'll have to draw it up to say for sure) to explode in grand fashion. however, in their explosion i am having some trouble telling what they are/were. I know who of them were IRF830, N-Channel Power Mosfets, I'd expect to see their complement P Channels on the other side of the grid, but am not sure, so here is my question:Is there someone out there who has a HP 16500A/B/C who is happy to pull its power supply (an 0950-1853) out remove the black plastic cover, and tell me what the power mosfets are on the four heat sinks more or less in the middle of the board?Cheers and thanksAndrew

author: tautech
author_rank: Super Contributor
timestamp: November 28, 2015, 05:44:41 am
content: Welcome to the forum.Haven't dowloaded and checked it....but this might help:https://www.cs.tcd.ie/SCSSTreasuresCatalog/hardware/TCD-SCSS-T.20150217.002/HP16500-90911-Service-Manual.pdf

author: electrogeek
author_rank: Contributor
timestamp: November 28, 2015, 05:47:41 am
content: Here are some pictures of the situation, First the whole board, then where the mosfets were that failed, and finally, the mosfets themselves.

author: electrogeek
author_rank: Contributor
timestamp: November 28, 2015, 05:49:31 am
content: thanks for the link, already read it, it suggests replace the power supplywithout any detail to its operation at all, I'd hoped for better really. any other suggests on things I should check before putting power back into the board would be most welcome.

author: tautech
author_rank: Super Contributor
timestamp: November 28, 2015, 05:58:13 am
content: I've seen threads here where some HP PSU's are supplied by other companies, so maybe someone will see this thread and give you a hand.Possibly you could find the schematic is a close copy of one found in a SMPS controller datasheet as a "typical application".What's the controller IC?

author: electrogeek
author_rank: Contributor
timestamp: November 28, 2015, 06:09:54 am
content: from the layout, i believe its an UC3524AN, however I'm not entirely sure, as it seems a bit of an odd choice for the job. mind you that might just be me being used to more modern designs

author: PaulAm
author_rank: Frequent Contributor
timestamp: November 29, 2015, 02:14:30 am
content: I have a 16500a sitting under a bench. I'll see if I can open it up and take a look. Might take me a day or two to get to it.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 29, 2015, 02:32:32 am
content: Hi,All four MOSFETs are almost certainly IRF830. Looking at the date code on the UC3524AN is 9029, 29th week of 1990.In 1990 there weren't any P Channel devices capable of the 400-450V required for this application.The IRF830 is 500V, 1.35Ohms RDSon, 4.5A.Let see if someone pulls their power supply.Regards,Jay_Diddy_B

author: PaulAm
author_rank: Frequent Contributor
timestamp: November 29, 2015, 04:54:08 pm
content: The two that I can see without taking anything apart are IRF830sMy board looks a little different; there are five large heatsinks on the left side.I'll upload a pic if my phone ever decides to pickup the correct ip addressOK, danged wireless router was serving the wrong address. Here's the pic of my PS. Q2 and Q5 were the ones I could identify.

author: electrogeek
author_rank: Contributor
timestamp: November 29, 2015, 09:15:41 pm
content: Thanks everyone, I'll order some MOSFETs and see how we go, anything else people think I should check in the area before powering it back up?

author: electrogeek
author_rank: Contributor
timestamp: November 30, 2015, 05:07:30 am
content: That's fantastic, looks exactly the same as mine before I removed the MOSFETs, I'll order some replacements and see if it lives, or what else failed...

author: cncjerry
author_rank: Unknown
timestamp: December 01, 2015, 09:56:28 pm
content: I bought those mosfets out of a guy in Florida. NOS, great deal. If you can't find them search for mosfet Florida.

author: TomBombadil
author_rank: Newbie
timestamp: November 07, 2017, 08:28:04 am
content: Did you have any success in repairing the PSU?Do you have any additional clues why the MOSFETs did blow up?I do also have a 16500A with similar symptoms - blown mosfets.I got an replacement psu, factory sealed, and powered the unit for a few seconds. There were signs of smoke of resistores underneath the mosfets.I think I've to check the caps in the output path.Any possibility to poweron the psu w/o load?