OT: Weird Hardware Problem

Valeri Galtsev galtsev at kicp.uchicago.edu
Wed May 20 19:25:36 UTC 2020

On 5/20/20 1:21 PM, Kevin P. Neal wrote:
> On Wed, May 20, 2020 at 11:07:32AM -0500, Valeri Galtsev wrote:
>> Yes, it was I who mentioned electrolytic capacitors. And that goes about
>> both PS and system board (the last mostly the ones situated around CPU).
>> The trouble is: not filtering well enough ripple on the power leads of
>> buses.
> Since we're on the subject, will problems with capacitors appear with a
> power supply that is boxed up unused?

It is less likely, but not fully excluded. It is safe to consider PS 
sitting on the shelf for some 7- 10 years as having some 30% smaller 
power rating.

Capacitors (electrolytic) age faster when they are heated, and and do a 
lot of charge/discharge big swings. That said, whether given 
electrolytic capacitor will deteriorate a lot, or almost not at all 
depends much more on its design, and after some period of using really 
poorly designed capacitors, manufacturers started shying away from them, 
and production of them diminished, mostly switched to better ones.

If you look at the system board ("motherboard" is common jargon for 
almost 30 years), you will see some capacitors are pre-cut on their top 
(but not cut through fully), others are not at all, and have smooth flat 
top. The first ones are the ones that are more likely to leak, and 
pre-cut top allows to not let build up high pressure, just break the top 
open at lower internal pressure if electrolyte boils in it. This 
prevents capacitor from exploding badly - I've seen the result once in 
ancient tube based radio once. Mess! So, the one's that have smooth flat 
top would usually be more robust.

> I have a five year old machine that I use for working from home. I was
> considering collecting parts for it so if I need to fix it quickly I can.
> But if those parts are going to go bad on me regardless of use then there's
> less incentive to spend money today.

This whole thing is not as awful as it may be, and significantly depends 
on how unlucky you are with your parts. I too collect old parts, and 
re-use them for diagnostics or repair.

I have seen leaked out capacitors on some video cards, which I disposed 
of right away. So, visual examination helps. If some capacitors are 
bulging, or have brown residue (which is leaked dried electrolyte), then 
they are bad. On occasion I even did a repair by replacing such 
capacitor (it was only one looking bad on that board) with good one. But 
that was some generic PCI[-*** whichever] board, probably video card, 
not system board. I didn't invest time into fixing system board by 
replacing leaked capacitors, usually they are too old at that point, it 
is just cheaper to get new machine.

I hope, this helps.


Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247

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