Bad capacitor or not? - Page 1
Forum section: electronics / projects

author: HSPalm
author_rank: Regular Contributor
timestamp: February 18, 2014, 01:17:08 pm
content: Hi,just received a free HP DPS-800GB A server psu for rack mount. It's a small unit but has 82.2A @12.15V so I want to fix it for a lipo charger psu.Anyways, the input fuse was blown and right next to it two capacitors and some black residue on the PCB and surrounding components. Took out the capacitors and they both measure just fine (identical to thishttp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270991230896). Now it seems the black residue origins from beneath one of the caps, and it has a slight damage/leakage sign at the welding point on the positive pin. But it measures fine both in capacitance and resistance, same as the good one (i suspect is good). These are the mans filtering caps. Is the voltage or frequency from the multimeter not enough to see the leakage?My question is if I should expect any more trouble, or just replace the caps and fuse and try again? The PSU was operative for maybe a week or so before it needed replacing.PS I removed the surrounding plastic film for inspection, it had cracked pretty badly anyways, probably from heat?

author: calexanian
author_rank: Super Contributor
timestamp: February 18, 2014, 08:06:10 pm
content: I have little experience with these, however those are United Chemi Con caps and those are pretty much top notch.

author: kripton2035
author_rank: Super Contributor
timestamp: February 18, 2014, 08:25:27 pm
content: did you check also the esr of the capacitor and compare to the other one ?if the fuse is blown, certainly another thing is dead : mains diode, mains mosfet due to bad esr capacitormust check before apply power, especially for 82 amps ...

author: johansen
author_rank: Super Contributor
timestamp: February 18, 2014, 08:51:58 pm
content: it looks like the supply simply arced over under the capacitor.. you'll notice there is 3mm between traces.. but there might only be half a mm gap between that rivet and the opposing trace on the pcb...you might not even need to replace the capacitor, nail polish or something more professional to cover the exposed copper.

author: HSPalm
author_rank: Regular Contributor
timestamp: February 18, 2014, 09:39:26 pm
content: I can agree on the arcing,you can see the actual spot very clear, and the missing solder stop is also a clear sign. Could this be a lightning strike maybe? What rivet?

author: johansen
author_rank: Super Contributor
timestamp: February 18, 2014, 11:15:08 pm
content: the capacitor's aluminum rivet which connects the internal foil, through the rubber seal to the brass/copper pin.. is definitely where the supply arced over to the opposing trace. i wouldn't wait for a new capacitor, just clean it up and re-install with additional insulation.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: February 18, 2014, 11:28:02 pm
content: Those bulk capacitors rarely fail, I agree that it's probably just an arc. Maybe a bug got in there and fried. Replace the fuse and you should be good.

author: Richard Head
author_rank: Frequent Contributor
timestamp: February 19, 2014, 06:35:01 am
content: The Nippon Chemicon and United Chemicon HV caps are excellent!I have used them in products that use a boost converter (450V rated) with almost a non-existant failure rate.It looks like the one that arced over underneath was due to insufficient clearance due to the diagonal placement of that cap.I agree, clean it up, check the bridge rectifier diodes/fuse/NTC and try it again.Good luck.

author: pancyber
author_rank: Newbie
timestamp: February 21, 2014, 08:37:06 pm
content: I repair hi power supplies for a living and during the last years, I have seen many busted high class computer supplies with just a busted capacitor.Replacing them saves the dat... the last victim was yesterday; a busted 900Watt Corsair unit... same picture as yours... Have in mind that big capacitors react differently when at full power. It may appear ok with the multimeter, but when in power... booom. I repair many treadmill boards with just a busted varistor. Unless I change the capacitor as well, as soon as I switch them on... booom the varistor cracks again. Those capacitors almost always measure OK...

author: Huluvu
author_rank: Regular Contributor
timestamp: February 22, 2014, 07:03:57 am
content: Quote from: pancyber on February 21, 2014, 08:37:06 pmbut as mentioned, those UCC / KMQ Types are good quality caps and not comparable with cheap "brands" used in computer power supplies where every cents counts.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: February 24, 2014, 07:13:50 am
content: Quote from: pancyber on February 21, 2014, 08:37:06 pmI'm curious where you found a Corsair 900W. Unless it was that old TX950 unit, but those are pretty scarce these days.