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

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
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -



"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

The power supply was turned on this morning at 8 am and shut down in less
than 10 minutes. I turned it back on about 9:30 and it is still on, that's
over 4 hours. I'm not that versed on ESR but I have a tester and cm
curious if high ESR can be an intermittent condition and if so what would
the physics of that phenomena be? At this point I'm not willing to do a
shotgun replacement of all the caps. I do keep running the power supply and
the condition is not getting worse. I wish it would fail so I might find
the failed component. The way it is now it's impossible to troubleshoot
without shotgunning.

--

73
Hank WD5JFR
"sofie" wrote in message
...
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
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -



"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

Henry Kolesnik wrote:

The power supply was turned on this morning at 8 am and shut down in less
than 10 minutes. I turned it back on about 9:30 and it is still on, that's
over 4 hours. I'm not that versed on ESR but I have a tester and cm
curious if high ESR can be an intermittent condition and if so what would
the physics of that phenomena be? At this point I'm not willing to do a
shotgun replacement of all the caps. I do keep running the power supply and
the condition is not getting worse. I wish it would fail so I might find
the failed component. The way it is now it's impossible to troubleshoot
without shotgunning.

A dried out cap is not an intermittent problem, but if the supply turns
off when some threshold is reached and that threshold has lowered
because of the cap's high ESR then the actual trigger would be caused by
power line fluctuations, temperature changes, etc.

A cold solder joint would be quite intermittent, but it would show up
with board flexing and other "wiggling" kind of diagnostics.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do an ESR test on the caps. Chances are you will only have a number of bad
caps. Sometimes it is best to cool and heat the caps under test. I use a
heatgun, and freeze spray to cool and heat them.

--

Jerry G.
======


"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

Henry Kolesnik wrote:
snipped:
At this point I'm not willing to do a
shotgun replacement of all the caps. I do keep running the power
supply and
the condition is not getting worse. I wish it would fail so I might
find
the failed component. The way it is now it's impossible to
troubleshoot
without shotgunning.




Henry:
Looking for cracked circuit board connections AND testing the
electrolytics with an ESR meter (or substituting electrolytics if you
do not have an ESR meter) is NOT "shotgunning".... it is real
troubleshooting advice as a result of the symptoms you posted. If you
continue to use it with the problem you reported it may fail completely
and be a bigger repair job.
Pay a little now Or pay a lot later.
electricitym

As of this moment it has run over 26 hours without shutting down. I've
never seen any evidence that ESR can be an intermittent phenomena. Can
someone please tell me how intermittent ESR comes about?

--

73
Hank WD5JFR
wrote in message
oups.com...
Henry Kolesnik wrote:
snipped:
At this point I'm not willing to do a
shotgun replacement of all the caps. I do keep running the power
supply and
the condition is not getting worse. I wish it would fail so I might
find
the failed component. The way it is now it's impossible to
troubleshoot
without shotgunning.




Henry:
Looking for cracked circuit board connections AND testing the
electrolytics with an ESR meter (or substituting electrolytics if you
do not have an ESR meter) is NOT "shotgunning".... it is real
troubleshooting advice as a result of the symptoms you posted. If you
continue to use it with the problem you reported it may fail completely
and be a bigger repair job.
Pay a little now Or pay a lot later.
electricitym

You should at least test the electrolytic caps in the startup circuit.

Since as I recall, it blows up only when applying AC power suddenly, something
funny is going on during startup.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.


"Henry Kolesnik" writes:

As of this moment it has run over 26 hours without shutting down. I've
never seen any evidence that ESR can be an intermittent phenomena. Can
someone please tell me how intermittent ESR comes about?

--

73
Hank WD5JFR
wrote in message
oups.com...
Henry Kolesnik wrote:
snipped:
At this point I'm not willing to do a
shotgun replacement of all the caps. I do keep running the power
supply and
the condition is not getting worse. I wish it would fail so I might
find
the failed component. The way it is now it's impossible to
troubleshoot
without shotgunning.




Henry:
Looking for cracked circuit board connections AND testing the
electrolytics with an ESR meter (or substituting electrolytics if you
do not have an ESR meter) is NOT "shotgunning".... it is real
troubleshooting advice as a result of the symptoms you posted. If you
continue to use it with the problem you reported it may fail completely
and be a bigger repair job.
Pay a little now Or pay a lot later.
electricitym

Henry Kolesnik:
It is NOT "intermittent ESR" that is the problem, rather it is that maybe
some electrolytics have developed high ESR and are operating just at or near
the threshold of the circuitry operating correctly... (see the reply post
from Tim Wescott).
At this point you have been given sound technical advice to check for
circuit board solder connections and to suspect the electrolytics......
until you perform this important initial suggested troubleshooting there is
not much more that you can do ??? Get this fixed right away before it
fails completely as you have previously been cautioned.
electricitym


"Henry Kolesnik" wrote in message
news
As of this moment it has run over 26 hours without shutting down. I've
never seen any evidence that ESR can be an intermittent phenomena. Can
someone please tell me how intermittent ESR comes about?

Henry Kolesnik wrote:

As of this moment it has run over 26 hours without shutting down. I've
never seen any evidence that ESR can be an intermittent phenomena. Can
someone please tell me how intermittent ESR comes about?

Who ever said ESR had to be intermittent to cause intermittent problems?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Henry Kolesnik wrote:
As of this moment it has run over 26 hours without shutting down.
I've
never seen any evidence that ESR can be an intermittent phenomena.
Can
someone please tell me how intermittent ESR comes about?


The measured ESR of an electrolytic capacitor changes with
temperature.... usually ESR decreases slightly. If the power supply
circuit is just at the threshold of operating correctly then very
slight changes in the ESR of critical capacitors will certainly affect
how the power supply operates and sometimes it can cause a catastrophic
failure of other components. Cold or cracked solder connections can
also cause similar intermittent symptoms.
The repair suggestion replies you have been getting to your original
posting are your FIRST troubleshooting and testing steps; otherwise we
are all guessing here.

wrote in message
ups.com...
Henry Kolesnik wrote:
As of this moment it has run over 26 hours without shutting down.
I've
never seen any evidence that ESR can be an intermittent phenomena.
Can
someone please tell me how intermittent ESR comes about?


The measured ESR of an electrolytic capacitor changes with
temperature.... usually ESR decreases slightly. If the power supply
circuit is just at the threshold of operating correctly then very
slight changes in the ESR of critical capacitors will certainly affect
how the power supply operates and sometimes it can cause a catastrophic
failure of other components. Cold or cracked solder connections can
also cause similar intermittent symptoms.
The repair suggestion replies you have been getting to your original
posting are your FIRST troubleshooting and testing steps; otherwise we
are all guessing here.


Just a guess here, as I may have missed a post or two, but does the unit
shut down "completely" to where nothing can be traced through to see where
it stops? IF not, maybe try that too. I agree with the rest otherwise.

L.