PSU cap replacement question - Page 1
Forum section: electronics / repair

author: Mephitus
author_rank: Regular Contributor
timestamp: July 31, 2015, 03:27:56 pm
content: I am in the process of troubleshooting/repairing a 750W PC PSU. (Waiting on probes for my new scope before I can fully diagnose) I am already pretty sure I will be replacing all the caps as part of the process. In regards to this, all but the mains filter caps seem to fall within range of aluminum polymer caps. Since their temperature rating, expected lifetime and stability greatly exceed the ratings of standard electrolytic caps, is there any real-world reason as to why it would be a bad idea to substitute them in? Alternatively, is there any advice you can give a newbie like me to increase the lifetime and reliability of a PSU since I am already repairing it?

author: DmitryL
author_rank: Regular Contributor
timestamp: July 31, 2015, 03:39:50 pm
content: Quote from: Mephitus on July 31, 2015, 03:27:56 pmIf you want reliability etc. first why don't you buy a modern decent quality PSU ?On the other hand, you can entertain youself by repairing a potentially badly designed PSU (it failed already, right?) blindly changing capacitors won't make its design better.E.g. its PCB can be laid out in such a way that capacitors (you are going to replace) placed really close to parts generating a lot of heat... missing "unnecessary" parts..

author: Mephitus
author_rank: Regular Contributor
timestamp: July 31, 2015, 04:24:44 pm
content: Quote from: DmitryL on July 31, 2015, 03:39:50 pmThe PSU is about 7 years old or so and was ridden pretty hard. Before it started acting up it was working like a champ. So cap working life failure really wouldnt surprise me at all. Nearly all the caps are mounted closest to the output rails, far away from the mosfets. I will take it apart and take a pic once I get home. (at work atm)My monthly budget for any hardware is only about $25. (Trying to get some savings in place to recover from a bankruptcy last year) So spending a few bucks on parts to repair it is my only realistic option if I dont want to run 2 PSU's all the time. Besides all of the above, I like to think of this as an educational opportunity.

author: cmptrdoctor
author_rank: Newbie
timestamp: July 31, 2015, 11:23:33 pm
content: In reference to your question about replacement caps, I have repaired several different types electronic devices over past years, most of them needing cap replacement, blown up, leaking, etc. I have always replaced the standard electrolytics with computer grade high temp 105C and low esr replacement types. In a few cases I went up one voltage level at same capacity, i.e replaced 16v cap with a 25v cap if physical size allowed and capacity was same. As far as changing to different type (aluminum polymer) I can't answer that as I've never attempted it.Hope it helps.

author: tautech
author_rank: Super Contributor
timestamp: August 01, 2015, 01:25:59 am
content: Quote from: Mephitus on July 31, 2015, 03:27:56 pmFor SMPS low ESR, High ripple current and frequency are important parameters to consider.Unless you can find caps that outspec the electroylitics normally used, stay with similar but well known brands. Panasonic, Nitchicon etc.