Henry:
As long as it is still w"working" the problem is not likely anything more
than either cold or cracked solder connection OR electrolytics that have
dried out or have developed high ESR. If you do not have an ESR meter then
you will have to use the "one by one" substitution method... or just replace
all of the electrolytics at once. Just about all other methods of testing
electrolytics will not provide the crucial ESR test needed especially for
electrolytics in switching power supplies and other high frequency or
critical circuitry.
DO NOT keep running your power supply with this problem.... it will only get
worse to the point that it will fail all together and be a much more
involved repair.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
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"Henry Kolesnik" wrote in message
om...
This is a 20 amp switching power supply for their 12 volt ham
transceivers.
I used to leave it on 24 hours a day on receive pulling less than an amp
with no problems but about a month ago it started to shut off. You have
to
turn it off first and wait about 15 minutes and it'll come back on,
sometimes for an hour or longer and other times for 5 to 10 minutes.
After
it goes down you have to turn it off and then wait 10 to 15 and it'll come
back for an unpredictable time. It doesn't seem matter if it been on for
an
hour or sometime 5 minutes, it'll shut down. It doesn't seem to be a cold
or
heat problem and flexing the board or tapping components won't turn it
off
or make it come on quicker. I don't have a schematic and can't find one.
It must have some kind of logic that senses something and makes it shut
down
and then time out. One thing I have noticed is that if I turn it on when
its not ready to come on I can hear a very, very faint noise (like static
discharge) that goes away as soon as the switch is turned off. It has a
TL494CN. Any tips appreciated.

--

73
Hank WD5JFR