HP 6012A power supply seems to be power limited (puts out 900W instead of 1KW) - Page 1
Forum section: electronics / repair

author: uoficowboy
author_rank: Regular Contributor
timestamp: May 28, 2016, 10:14:19 pm
content: Hi - I have an HP 6012A that I'm trying to bring to life. It's almost there... The one thing left is that it seems to be power limited. Using a Acme PS2L-1000 active load I've been testing its output capabilities. Regardless of the output voltage, I seem to only be able to pull ~850-900W from it.Any ideas as to what would cause this? I'm thinking maybe the input caps could be too old and they can't keep the internal supply up high enough?I should mention that the symptom is that when I pull ~850-900W the "output unregulated" light turns on on the 6012A.Thank you!

author: JFJ
author_rank: Regular Contributor
timestamp: May 28, 2016, 11:24:28 pm
content: Quote from: uoficowboy on May 28, 2016, 10:14:19 pmThat, with the other indicators off and the meters reading high, is the way that the supply indicates an overload condition. Are the rear terminals wired for Normal Operating Mode (as per attachment)?

author: PTR_1275
author_rank: Frequent Contributor
timestamp: May 29, 2016, 12:43:21 am
content: A setup close to my heart.I am looking at the rack on my bench with a Acme PS2L-1000 load with a HP 6012A sitting directly above it.Unfortunately I don't have any advice for you on this one, but I am interested to follow this thread and find out what the problem is.

author: uoficowboy
author_rank: Regular Contributor
timestamp: May 29, 2016, 06:34:16 am
content: Quote from: JFJ on May 28, 2016, 11:24:28 pmYes, I have the rear terminals connected as shown there.I have also seen that light turn on when the regulation circuit was confused. I had this problem when the connector between the main board and the control board had some busted contacts.Quote from: PTR_1275 on May 29, 2016, 12:43:21 amIt's a loud setup! By the way - have you seen a full manual and schematic for the PS2L-1000? I have seenthis one, but it is missing some sections (for example, it does not call out any voltage regulation for the +/- 15V supply)

author: PTR_1275
author_rank: Frequent Contributor
timestamp: May 29, 2016, 07:40:27 am
content: Unfortunately that is the copy of the manual I have printed in the library. It only seems to be missing page 26, so I am not sure what is on that page.Yes it gets a bit loud, but I do also get used to it. A few months ago when I stripped the workbenches and started from scratch, there was 4 days with no equipment running and it was eerie. Normally I have the whirr of the various UPS / computer / power supply fans to break up the silence. If I have all my DC loads running, then it gets loud (HP 6050 6 slot mainframe, Acme PS2L, 3H Industries Swinger 2 100A and 3H Industries Swinger 2 300A). You can feel the airflow out the back of the 300A swinger 2 from about 4 meters away.

author: uoficowboy
author_rank: Regular Contributor
timestamp: May 30, 2016, 04:04:09 am
content: Quote from: uoficowboy on May 28, 2016, 10:14:19 pmNope, wasn't that. At no load, the input caps are at ~339VDC with 0.1VAC. At 850W, the input caps were at 306VDC with 2VAC. I doubt the 10% drop is going to cause it to lose the ability to regulate.Next I need to go through the schematics for this thing and try to remember how it does power limiting.

author: nctnico
author_rank: Super Contributor
timestamp: May 30, 2016, 01:38:32 pm
content: Maybe it's the load combined with the PSU's control loop. I'd try to use a couple of resistors or a different load before digging into the 6012A.

author: uoficowboy
author_rank: Regular Contributor
timestamp: May 30, 2016, 06:36:57 pm
content: OK - found the problem. I had been trying to find the power limiting circuit in the schematics but was looking in the wrong place, expecting it to be feeding into the CV and CI circuits. It was instead after those circuits get combined. It is adjustable via pot R20. I had to turn it about 20-30 degrees clockwise and now I can hit the rated output of my 6012A. Now the PS2L-1000 is the one that starts getting grumpy at too high of power (when I push it past 1KW). So we're all good here.

author: PTR_1275
author_rank: Frequent Contributor
timestamp: May 31, 2016, 12:07:20 am
content: Good to hear you found the fix.