HP 6024A bench supply magic smoke... - Page 1
Forum section: electronics / general

author: MadModder
author_rank: Regular Contributor
timestamp: March 18, 2013, 06:43:52 pm
content: I bought a used bench supply 5 years ago. A HP 6024A.The high noised fan inside got to my nerves and I decided to change it for something else.But it was a mains driven fan, and I only had 12V fans.So I tried to hook the 12VDC-fan to one of the unregulated rails, via a voltage regulator. The +5V unregulated rail, which was +16V.It was a VERY bad idea to do it while the supply was running.It went POOF POOF!I reccon I disturbed something with the feedback loop, so the powerswitching fets stayed open and broke, and thereby blew the resistors in the gate circuit. Just a theory.I haven't taken the time to dig in to it yet. I have other bench supplies, but it's a pitty to have a great supply just standing there collecting dust.Every voltage on the front controller board are like they should according to the schematic, but the angry red LED on the front saying "unregulated" lights up as soon as I start the thing. Nothing on the output terminals.This is what I saw when I opened it. Three blown resistors. (marked with red). I have replaced them, but no dice.The transistors further away outside the picture must have blown also. I haven't looked into that. Nothing visible though.Anyone got other ideas?

author: valentinc
author_rank: Regular Contributor
timestamp: March 21, 2013, 10:21:05 pm
content: Do you have the schematic ? I can't find it...

author: MadModder
author_rank: Regular Contributor
timestamp: March 24, 2013, 05:31:10 pm
content: Yes I have. It'shere.For my unit I should make manual changes 1 to 12 according to the table of erratas.

author: ConKbot
author_rank: Super Contributor
timestamp: March 26, 2013, 02:55:08 am
content: I too have a broken 6024A with a few burned out components around the gate drive area. Quite an interesting topology they have, with the separate turn on and turn off gate drive transformers, and what looks like a dual switch forward or flyback converter, but the manual flatly states its operating in flyback modeUnfortunately the fets are listed as "FET- T03" which his highly helpful :p and the label on the TO-3 can is "5-486" by motorola again, unhelpful in my searches so far. Just turning up stuff about RF transistors. They were made in 91, so not super old. So hopefully they arent blown, as I dont feel like trying to guess the specs on an NTE replacement which will work.Good luck, I'll be getting to attempt to repair mine at one time or another here soon.

author: americanhacker1
author_rank: Newbie
timestamp: March 30, 2013, 04:57:19 am
content: if you can repair the unit you can always just hook up another 12v fan but use a 12v dc wall wart and put it where the fan normally goes just with a second cable coming out and I would recommend installing a switch so you can control when it is on or even run it to the main switch you have already on there just a recommendationhave fun

author: MadModder
author_rank: Regular Contributor
timestamp: April 01, 2013, 09:13:36 am
content: A few days after the incident I constructed a mains driven temperature controlled fan controller to drive a 12VDC fan. I'll hook it to the mains switch.It doesn't solve the current problem though...

author: MadModder
author_rank: Regular Contributor
timestamp: September 29, 2018, 11:31:08 am
content: When you least expect it...Today I found a physical printed service manual on ebay (together with a CD), so I ordered it.This rather bulky paper weight has been sitting in a box for too long now.I hope this will aid me more in the repair than the unreadable PDF available online.