HP 53131A Power Supply Failing - Page 1
Forum section: electronics / repair

author: wriely
author_rank: Contributor
timestamp: July 16, 2025, 04:08:57 am
content: I recently acquired a HP 53131A power supply with the Delta DPS-43 DP-2 power supply in it. It worked fine for about 12 hours. I then unplugged it for a few days while re-organizing my bench to make room for it. Upon plugging it back in, I just heard a clicking sound from it and it would not power on.I opened it up again to see if I could find the problem. Upon applying power (plugging it in), I saw that the fan was trying to spin but failing to do so. I gave it a manual spin and it slowly started spinning up and after 10-15 seconds, and the clicking sound stopped as well. Now pressing the power button brought the unit up normally and passed the self test.I took a thermal image while operating to see if anything jumped out, but it looks normal to me:I did some digging around on here and came across the JF2014 power supply schematic for the HP 531XX units. I'm ready to remove the board and start testing the obvious components (semiconductors, capacitors). Anyone have any experience with this particular power supply have any hints for me? I'm wondering if maybe the fan is overloading the +12V output and causing it to briefly shut down. I should probably order a replacement as it's a noisy thing anyway.--Walt

author: lowimpedance
author_rank: Super Contributor
timestamp: July 16, 2025, 05:42:33 am
content: The first port of call is replacement of the electrolytic caps and clean up any electrolyte leakage if any. Check for dry joints too.Others have discovered bad resistors and ceramic capacitors. I would at least check all resistors for any open or drifted high etc.Retest after the electro cap and fan change to see if it works or any signs of life.I have fixed 3 units with just the electrolytic cap change. YMMV

author: wriely
author_rank: Contributor
timestamp: July 16, 2025, 02:55:56 pm
content: Quote from: lowimpedance on July 16, 2025, 05:42:33 amMy unit has no evidence of any electrolytic leakage which is a pleasant surprise given it was manufactured in the mid 1990s when the plague was near its peak. They appear to be mostly Rubycon units.My OCD requires that I first find out what is wrong with the instrument before fixing it.All electrolytics will be replaced once the root cause of the failure is found.It's headed for dry dock shortly.

author: Qw3rtzuiop
author_rank: Frequent Contributor
timestamp: July 16, 2025, 08:40:14 pm
content: Quote from: wriely on July 16, 2025, 02:55:56 pmI've repaired multiple units. Replace those electrolytics at first sight. They don't leak that much if all, but loose capacity from the many hours of runtime in between the hot PSU components. Replacing is easy, only costs a few bucks and is definitely necessary.

author: Runco990
author_rank: Frequent Contributor
timestamp: July 16, 2025, 09:08:43 pm
content: This is a super documented issue. Aging capacitors. Why even bother to troubleshoot in this case. But if you MUST, start with the small caps that start and feed back the PSU.While you are at it, replace the fan with a Noctua attached with rubber mounts. You'll love it! Barely a whisper. I never leave mine plugged in, as the PSU runs all the time, regardless if you have the OCXO installed or not. I use an external reference anyway, and it keeps the useless hours off the PSU.

author: wriely
author_rank: Contributor
timestamp: July 16, 2025, 10:46:50 pm
content: For me, troubleshooting failed instruments is the fun part of ownership. At least until I'm ~100 hours or so into troubleshooting with nothing to show for it!This will be plugged in all the time so the quiet fan will be a welcome update. I'm not as worried about the PSU aging as I am about waiting for the OCXO to warm up for 24 hours every time I want to use it.I'll report back what the issue was when I get it solved. Might take a few days though as I've not yet ordered parts for it. First need to measure all the cap sizes and pin spacings so I can get replacements that fit nicely.

author: TERRA Operative
author_rank: Super Contributor
timestamp: July 17, 2025, 04:45:41 am
content: I am 3 for 3 on bad electrolytic capacitors on these power supplies.I also had one that had some bad ceramic capacitors too.Just replace all the electrolytic capacitors with high ripple current rated, low ESR types from a reputable manufacturer. Any fault finding before doing that is just a waste of time.

author: dhillman
author_rank: Contributor
timestamp: July 17, 2025, 07:12:01 am
content: Be cautious when acquiring capacitors for the output pi filters. Too low an ESR will push the power supply feedback loop out of stability at higher loads. This is especially the case for after market OCXOs during warmup.

author: wriely
author_rank: Contributor
timestamp: July 30, 2025, 11:52:26 pm
content: Quick update:All of the Rubycon YXB capacitors on my board showed signs of leaking when removed. C102 (2200uF) had completely failed and leaked the worst. C102, C103, C104, and C152 (all 1000uF) showed minimal signs of leaking and all tested OK for value and ESR, but of course they are being replaced. All remaining capacitors showed absolutely no signs of leaking and tested within specifications. Most were stamped YXL. I was unable to find a suitably-sized replacement for C1 (150uF/400V) at Mouser. The existing capacitor is 25mm high by 31mm in diameter with a 10mm lead spacing. I'm sure the supply will run fine until I can locate a suitable replacement for it.I expect the factory Delta fan is fine, but I don't like the noise, especially on a supply that runs continuously. Mouser doesn't carry the Noctua that was recommended, but they do have Sunons which should do nicely (21 dBA).All of the capacitors on the board have PCB holes which are spaced 5mm apart with the exception of C1 which is spaced 10mm apart. C1, C102, C103, C104, and C152 were all mounted flush with the remainder having formed leads which extend a few mm above the board.The supply was pleasantly easy to remove, with just three screws holding it in place and an easily unplugged connector to the main board.Based on my findings, I'd say that the completely failed C102 explains the symptoms I was experiencing. Given the single-sided PC board, there is little risk in replacing all of the capacitors with the only annoyance being the large amounts of glue that was used to secure the capacitors against vibrations. I'll add the Rubycon YXB to my growing list of "replace on sight" electrolytics for future repairs.