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Power Supply Cap Basic Replacement Advice

Discussion in 'Troubleshooting and Repair' started by eludema, Sep 1, 2018.

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  1. eludema

    eludema

    2
    0
    Sep 1, 2018
    Hi folks! Friendly looking forum! I'm excited to dig around to learn lots on this crazy journey of learning basic electronics.

    So yes, I'm a noob. I've read a lot, checked out a lot of videos, read a couple of good books, and proudly (and successfully) built a few Radio Shack projects, woot! This was all because I can't afford to buy new PA speakers to replace my Behringer Eurolive 212D's that have been fritzing out -- and I need my speakers back! (full-time music professor = no budget ;). So disclaimer done. Here come the questions (with a little background):

    - The issue is definitely with the power supply, and most surely the caps. A few are visibly bloated, and using a cheap ESR meter on all the caps, 20 out of 31 test too low on board. The speaker doesn't keep its charge for more than a split second, but after power-cycling the thing around 20 times, it stays on. It gradually got worse after time... again, from what I've read, a cap issue. All the caps are Decons (SH/SAII/SHL @ 105 or 85C) with a few KSDs (85C), and from my reading, it's best just to swap them all out for higher grade and more reliable Japanese caps... QUESTION: Panasonic or Nichicon or ...? Or does it matter (which of those higher end brands)? I'll be sure to keep capacitance the same and aim to keep the voltage the same or a little higher. I'm also thinking of increasing all the 85C caps to 105C... Am I on the right track?

    - What are the go-to online stores to buy parts? I don't need massive bulk, since I'm only planning on repairing things only when I really have to! But I'm sure buying each cap separately would cost more than if I bought 10 or so of each type... Is Mouser the way to go? Unfortunately, I don't have a brick-and-mortar around for easy access.

    - What the heck is the black glue holding some of the caps together and down to the board? I know it's most likely to prevent vibration damage. I've seen online super glue, silicone (clear) adhesive, epoxy, RTV something or other... etc. But I can't tell what kind of adhesive I have on this PCB. See the attached photo... I can pick it off with my fingernail and it feels like silicone, but I'm not sure... If I don't buy the exact same material, what would a good (or better) alternative be?

    I'll leave it at that for now. I don't want to waste too much of your time on free advice!

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  2. Bluejets

    Bluejets

    3,766
    781
    Oct 5, 2014
    Power supply problems can be crook caps but I don't see any indication of that.
    Glue is just glue, anything would suffice, hot glue, bear contact cement.
    As far as in-circuit testing, don't think you can rely on that as other components may have an affect on the readings.
     
  3. H2814D

    H2814D

    75
    9
    Nov 4, 2017
    As someone who has been going through a lot of cap replacing lately, I can tell you the same. Remove the caps from the board prior to testing them. If you are going to replace, stay with the same uF rating. Voltage should be the same or higher, but never lower. Higher temp ratings usually indicate a better replacement, but staying with the same is fine. Pull the larger caps first, as it seem they are usually the ones that go bad first. Definitely pull the ones that are bulging or have any indication of leaking. I think you will find the larger bulging ones may be the only ones you need to replace, if the issue is only cap related. You are on the right track as far as a source for parts. The larger caps are necessarily more expensive, so buying in bulk is kind of foolish. Let us know if your work is successful.
     
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