Switch mode power supply

[Joe]

Hi,

I have a 9V, 0.75A switch mode power supply which has a strange problem. It
does not work (i.e. no voltage output) unless I _slowly_ slide in the IEC
mains lead (so that it sounds like there is some arcing) the first time I
use it for a while. If I just plug in the mains lead quickly or turn on the
socket at the wall it does not work. After it has worked once, and the unit
is slightly warmer perhaps, it operates fine. I can turn it off and on again
at the wall socket with no problems.

Any ideas?
Joe.

 

[Sam Goldwasser]

"Joe" <anon@anon.com> writes:

Hi,

I have a 9V, 0.75A switch mode power supply which has a strange problem. It
does not work (i.e. no voltage output) unless I _slowly_ slide in the IEC
mains lead (so that it sounds like there is some arcing) the first time I
use it for a while. If I just plug in the mains lead quickly or turn on the
socket at the wall it does not work. After it has worked once, and the unit
is slightly warmer perhaps, it operates fine. I can turn it off and on again
at the wall socket with no problems.

Usually, problems that disappear when something warms up are either
bad connections or dried up electrolytic capacitors - the latter being
more likely in this case.

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Important: The email address in this message header may no longer work. To
contact me, please use the feedback form on the S.E.R FAQ Web sites.

 

[Sofie]

Joe:
Very likely the problem you described is caused by faulty or high ESR
electrolytics...... don't continue nursing this problem along..... soon,
you may not be able to get it to work at all and additional components
including the switching transistor or chip may fail. If you do not have an
ESR meter, just replace ALL of the electrolytics.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


"Joe" <anon@anon.com> wrote in message
news:ykt_b.2656$396.1519@newsfe3-win.server.ntli.net...

Hi,

I have a 9V, 0.75A switch mode power supply which has a strange problem.
It
does not work (i.e. no voltage output) unless I _slowly_ slide in the IEC
mains lead (so that it sounds like there is some arcing) the first time I
use it for a while. If I just plug in the mains lead quickly or turn on
the
socket at the wall it does not work. After it has worked once, and the
unit
is slightly warmer perhaps, it operates fine. I can turn it off and on
again
at the wall socket with no problems.

Any ideas?
Joe.

 

[Joe]

Thank you both for the advice.
Joe

"Sofie" <sofie@olypen.com> wrote in message
news:103l3m8hvau1s32@corp.supernews.com...

Joe:
Very likely the problem you described is caused by faulty or high ESR
electrolytics...... don't continue nursing this problem along..... soon,
you may not be able to get it to work at all and additional components
including the switching transistor or chip may fail. If you do not have
an
ESR meter, just replace ALL of the electrolytics.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


"Joe" <anon@anon.com> wrote in message
news:ykt_b.2656$396.1519@newsfe3-win.server.ntli.net...
Hi,

I have a 9V, 0.75A switch mode power supply which has a strange problem.
It
does not work (i.e. no voltage output) unless I _slowly_ slide in the
IEC
mains lead (so that it sounds like there is some arcing) the first time
I
use it for a while. If I just plug in the mains lead quickly or turn on
the
socket at the wall it does not work. After it has worked once, and the
unit
is slightly warmer perhaps, it operates fine. I can turn it off and on
again
at the wall socket with no problems.

Any ideas?
Joe.

 

[w_tom]

Heat being a significant factor, then you should also know
about the inrush current limiter. When it gets warmer, then
it conducts electricity. Cold - it may limit power so small
that power supply cannot start. However you don't know
anything about that supply until you take some multimeter
readings. This assumes (of course) that you intend to repair
this supply.

Joe wrote:

Thank you both for the advice.
Joe

"Sofie" <sofie@olypen.com> wrote in message
news:103l3m8hvau1s32@corp.supernews.com...
Joe:
Very likely the problem you described is caused by faulty or
high ESR electrolytics...... don't continue nursing this problem
along..... soon, you may not be able to get it to work at all and
additional components including the switching transistor or chip
may fail. If you do not have an ESR meter, just replace ALL of
the electrolytics.