COM ports not working? Check the PSU!

Discussion about old PC hardware.

COM ports not working? Check the PSU!

Postby mcobit » 2018-2-05 @ 16:55

The title says it all. Took me 2 days to figure out why nothing wanted to work on the com ports of my vlb interface card.

5V rail was at about 4V when my soundcard started making strange noises. After replacing the PSU. Everything is fine again.
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Re: COM ports not working? Check the PSU!

Postby bjwil1991 » 2018-2-05 @ 17:27

The PSU in my Packard Bell Pack-Mate 28 Plus is original, and every voltage (+/-5VDC and +/-12VDC) is still rock solid. I've had ATX PSUs that were losing voltages left and right, so I ended up tossing them out since they were way beyond repair (some of the caps were hard to find, and have temperatures up to 85C, which the PSUs require 105C caps).
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Re: COM ports not working? Check the PSU!

Postby cyclone3d » 2018-2-05 @ 18:00

bjwil1991 wrote:The PSU in my Packard Bell Pack-Mate 28 Plus is original, and every voltage (+/-5VDC and +/-12VDC) is still rock solid. I've had ATX PSUs that were losing voltages left and right, so I ended up tossing them out since they were way beyond repair (some of the caps were hard to find, and have temperatures up to 85C, which the PSUs require 105C caps).


And that is why, when replacing caps, that you don't necessarily have to use the same exact values. Generally, as long as you use something that can handle as much or more than the original caps, you are fine as long as they are the same type of cap.

For the caps that have problems dying, they were most likely junk in the first place and could not handle what they were rated for.
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Re: COM ports not working? Check the PSU!

Postby CkRtech » 2018-2-05 @ 20:08

Funny thing about caps is that the printed stuff like voltage, uF, and temperature have good wiggle room while the unprinted stuff like ESR and ripple are a little more important (imho).
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Re: COM ports not working? Check the PSU!

Postby gdjacobs » 2018-2-06 @ 00:02

Capacitance is the least important metric, except perhaps for bulk capacitors (which seldom need replacement).
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