I have a power supply for an lcd monitor that only works after being
heated. It will work fine so long as the monitor is kept on. After
cooling down, it's difficult to get started again. Occasionally it
will start with being unplugged and replugged, but usually it requires
heating. Eight minutes in the oven at 300F works consistently (wrapped
in a thin towel).

In the past I've had reasonable luck with this kind of failure just by
starting with the largest cap and pulling them until I find one that's
obviously leaking or shorted (testing with an ohm meter). This time,
however, the broken part isn't obvious to me.

I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?

I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?

Holding the can upside down worked a bit better. :-p

wrote:
I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?

Holding the can upside down worked a bit better. :-p

So you got a result? What was it?

Sylvia.

On May 6, 5:38*pm, Sylvia Else wrote:
wrote:
I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?

Holding the can upside down worked a bit better. :-p

So you got a result? What was it?

Sylvia.

Yes. Inverting the can gives a nice shot of cold liquid that rapidly
evaporates. I quickly found that cooling one of the smaller
electrolytics would switch off the power, so I'm fairly confident that
it's the culprit.

Unfortunately it's a low esr cap, and I haven't found a way to get one
to my door for less than 12 times the cost of the cap (due to minimum
shipping costs). It nearly eliminates the advantage of repairing the
supply.

I can get a non-esr replacement locally. Any guess how long that would
last?

The local shop only carries NTE parts. At first glance, I can't find
low esr caps in their catalog.

wrote:
On May 6, 5:38 pm, Sylvia Else wrote:
wrote:
I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?
Holding the can upside down worked a bit better. :-p
So you got a result? What was it?

Sylvia.

Yes. Inverting the can gives a nice shot of cold liquid that rapidly
evaporates. I quickly found that cooling one of the smaller
electrolytics would switch off the power, so I'm fairly confident that
it's the culprit.

Unfortunately it's a low esr cap, and I haven't found a way to get one
to my door for less than 12 times the cost of the cap (due to minimum
shipping costs). It nearly eliminates the advantage of repairing the
supply.

I know the feeling. Hard to understand why suppliers are unwilling to
put $5 worth of components in an envelope and send it by normal post.
Particularly if the customer expressly accepts the risk of its getting lost.


I can get a non-esr replacement locally. Any guess how long that would
last?

http://www.illinoiscapacitor.com/upl...18FF09455A.pdf

Doesn't sound like a good idea.

Sylvia.

I know the feeling. Hard to understand why suppliers are unwilling to
put $5 worth of components in an envelope and send it by normal post.
Particularly if the customer expressly accepts the risk of its getting
lost.

There's the overhead of picking and packing the products. Consequently, most
companies have a $20 to $30 minimum purchase, or impose an handling charge
for smaller orders. Some don't.

wrote in message
...
On May 6, 5:38 pm, Sylvia Else wrote:
wrote:
I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?

Holding the can upside down worked a bit better. :-p

So you got a result? What was it?

Sylvia.

Yes. Inverting the can gives a nice shot of cold liquid that rapidly
evaporates. I quickly found that cooling one of the smaller
electrolytics would switch off the power, so I'm fairly confident that
it's the culprit.

Unfortunately it's a low esr cap, and I haven't found a way to get one
to my door for less than 12 times the cost of the cap (due to minimum
shipping costs). It nearly eliminates the advantage of repairing the
supply.

I can get a non-esr replacement locally. Any guess how long that would
last?

The local shop only carries NTE parts. At first glance, I can't find
low esr caps in their catalog.


Depending where in the circuit the cap is, a 'normal' ESR cap will probably
work just fine for a considerable time. There are various things that you
can do to help its life, not the least of which is to make sure that it is
not pressed up close to a heatsink or power resistor. Also, try to get a 105
degree temperature rated cap, rather than an 85 degree. Your local supplier
should carry those, if not low ESR ones. The ESR of 'standard' caps can be
helped by connecting two in parallel, so that might be another thing to try
if you have room to get two in, or one on the front and one on the back of
the board.

A final thing that you could try, if you get desperate, is to try your local
repair shop. They would definitely carry low ESR caps for their own repairs,
and might be persuaded to sell you one. Failing that, they would almost
certainly have a scrap power supply board around from something - TV, VCR,
computer etc - that you could persuade them to part with. A 'replacement'
cap could then be 'culled' from that board. Obvious word of caution. Any
such second-hand cap might be as bad as the one you're replacing, and an ESR
meter would be useful to check, but in my experience, as long as the scrap
power supply that it's coming from is not too old, and the cap is not
located right next to a heat source, chances are it will be ok.

Hope that helps. If you are seriously into repairing this sort of stuff,
your very next investment should be an ESR meter (see Bob Parker's "Blue" at
Anatek Corp's website). This is an excellent instrument and very reasonably
priced. It will save you literally hours of wasted time and cans of freezer.

Arfa

wrote:
On May 6, 5:38 pm, Sylvia Else wrote:
wrote:
I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?
Holding the can upside down worked a bit better. :-p
So you got a result? What was it?

Sylvia.

Yes. Inverting the can gives a nice shot of cold liquid that rapidly
evaporates. I quickly found that cooling one of the smaller
electrolytics would switch off the power, so I'm fairly confident that
it's the culprit.

Unfortunately it's a low esr cap, and I haven't found a way to get one
to my door for less than 12 times the cost of the cap (due to minimum
shipping costs). It nearly eliminates the advantage of repairing the
supply.

I'm assuming that the cap is in the PSU. Have you got a spare PSU you
could cannibalise for parts? (I usually have a bunch of spare PSUs in
the junkbox.)

I can get a non-esr replacement locally. Any guess how long that would
last?

In the PSU? - Not long. It's also kind of begging it to let out the
confetti. ;^)

The local shop only carries NTE parts. At first glance, I can't find
low esr caps in their catalog.

I've never been desperate enough to pay the 10000% markup for NTE parts.


--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

On May 7, 6:11*am, Bob Larter wrote:
The local shop only carries NTE parts. At first glance, I can't find
low esr caps in their catalog.

I've never been desperate enough to pay the 10000% markup for NTE parts.

Heh. Well, a $0.63 part online is about $1.30 bubble-packaged from NTE
at the local shop. With minimum shipping being about $8, that's $8.63
vs. $1.30 for NTE. The markup isn't so absurd in that context.
Obviously for large orders it doesn't make sense.

On Wed, 6 May 2009 22:46:56 -0700 (PDT), wrote:

On May 6, 5:38*pm, Sylvia Else wrote:
wrote:
I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?

Holding the can upside down worked a bit better. :-p

So you got a result? What was it?

Sylvia.

Yes. Inverting the can gives a nice shot of cold liquid that rapidly
evaporates. I quickly found that cooling one of the smaller
electrolytics would switch off the power, so I'm fairly confident that
it's the culprit.

Unfortunately it's a low esr cap, and I haven't found a way to get one
to my door for less than 12 times the cost of the cap (due to minimum
shipping costs). It nearly eliminates the advantage of repairing the
supply.

I can get a non-esr replacement locally. Any guess how long that would
last?

The local shop only carries NTE parts. At first glance, I can't find
low esr caps in their catalog.

www.digikey.com

Probably about $.40 for the cap, $2.00 shipping and handling.

PlainBill

On Wed, 6 May 2009 22:46:56 -0700 (PDT), wrote:



Unfortunately it's a low esr cap, and I haven't found a way to get one
to my door for less than 12 times the cost of the cap (due to minimum
shipping costs). It nearly eliminates the advantage of repairing the
supply.

I can get a non-esr replacement locally. Any guess how long that would
last?

The local shop only carries NTE parts. At first glance, I can't find
low esr caps in their catalog.

It all depends on the circuit, and the quality of the cap. A good
quality regular cap will out last these junky "low ESR" caps that are
being used a lot. If nothing else, it will work until you need
something else that makes the order worth while.
Andy Cuffe

wrote:
I have a power supply for an lcd monitor that only works after being
heated. It will work fine so long as the monitor is kept on. After
cooling down, it's difficult to get started again. Occasionally it
will start with being unplugged and replugged, but usually it requires
heating. Eight minutes in the oven at 300F works consistently (wrapped
in a thin towel).

In the past I've had reasonable luck with this kind of failure just by
starting with the largest cap and pulling them until I find one that's
obviously leaking or shorted (testing with an ohm meter). This time,
however, the broken part isn't obvious to me.

I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?

A 400 watt Weller Soldering Gun applied to the top of electrolytics
has worked for me in the past. How big was your iron?

wrote:
I thought that perhaps I could isolate it by heating or cooling parts
until the unit started or stopped working. I tried using a soldering
iron for heating, and canned air for cooling, but neither had a clear
effect. Is there any other technique I might use for heating or
cooling individual parts?

Hairdryers on low are good if you're careful not to overheat components.
You can localise the area heated by cutting a hole of the desired size
in a sheet of cardboard & using it as a mask to shield the rest of the PCB.

If you haven't already done so, look for dry joints in the PSU.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------