Re: Darned capacitors again!


Dan Kerl wrote:

I have a similar tale to share about an oven controller.

This episode reminded me of the subtle ways that electrolytic caps can cause problems that are not obvious, particularly the noise. If erratic behavior in an electronic device is a problem, there's a good chance that an electrolytic is at the bottom of it.
Another tale: we have a his/hers digital alarm clock (2 alarms).
A few months back, it "went crazy" running much faster than
normal. I investigated, and found that the 9V battery backup
was only ~ 4 volts, so I replaced the battery, and all was well.
The damn thing failed again last Friday - same symprom. Sure
enough, the battery was below 5 volts. Another symptom was
thatt he clock display blinked at a very fast rate when the battery
was unplugged (I thought that was normal) .*This* time, I knew it
wasn't a simple battery failue due to old age. I metered the current
drawn from the new battery - sure enough, I found ~90 ua draw.
The clock is nothing more than a big LSI chip, some wires and
buttons, a couple of resistors - and 1 electrolytic cap.
I replaced the cap, which showed over 16 meg resistance.
Now the clock does not blink when the battery is out, and my DMM
cannot detect any current draw from the battery, and the clock is
working. This was a case where the battery hid the failure - as long
as it was in and good, the clock performed flawlessly, even with
the bad cap, (220uf 16v) I probably would not have thought of
the cap being bad had it not been for the ongoing discussion here.

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