LCD monitor internal power supply repair

[n]

Hi,

I"ve got a Northgate 17" LCD monitor who's warranty expired the 4th and
just gave out on me! Go figure - 15 days after the warranty dies...

I have isolated the problem to the internal power supply but need help
determining the exact problem.

THe problem is intermittant. When the problem does occur, the 100 uF,
400 Volt capacitor buzzes. At first I thought it was the capacitor (on
the ac incoming (primary) side. But I think the capacitor may be just
reacting to a fluctuating power level - maybe from a bad step down
transformer. I desoldered the capacitor and plugged the monitor in. It
buzzed - but only once - as opposed to several times with the capacitor
in place.

Any suggestions or ideas to look would be appreciated.

Much thanks.

 

[Ken Weitzel]

Hi,

I"ve got a Northgate 17" LCD monitor who's warranty expired the 4th and
just gave out on me! Go figure - 15 days after the warranty dies...

I have isolated the problem to the internal power supply but need help
determining the exact problem.

THe problem is intermittant. When the problem does occur, the 100 uF,
400 Volt capacitor buzzes. At first I thought it was the capacitor (on
the ac incoming (primary) side. But I think the capacitor may be just
reacting to a fluctuating power level - maybe from a bad step down
transformer. I desoldered the capacitor and plugged the monitor in. It
buzzed - but only once - as opposed to several times with the capacitor
in place.

Any suggestions or ideas to look would be appreciated.

Much thanks.

Hi...

Wouldn't it have been a much wiser test to replace the cap
instead?

Ken

 

[JANA]

I would think it would be most intelligent to replace the capacitor!

--

JANA
_____


Hi,

I"ve got a Northgate 17" LCD monitor who's warranty expired the 4th and
just gave out on me! Go figure - 15 days after the warranty dies...

I have isolated the problem to the internal power supply but need help
determining the exact problem.

THe problem is intermittant. When the problem does occur, the 100 uF,
400 Volt capacitor buzzes. At first I thought it was the capacitor (on
the ac incoming (primary) side. But I think the capacitor may be just
reacting to a fluctuating power level - maybe from a bad step down
transformer. I desoldered the capacitor and plugged the monitor in. It
buzzed - but only once - as opposed to several times with the capacitor
in place.

Any suggestions or ideas to look would be appreciated.

Much thanks.

 

[n]

Hi,

I've checked the capacitor - and the DMM readout matches the
specification - it's 100uF and it reads between 100 - 102 uF - perfect.
No signs of leakage that occurs sometimes in power supply caps over time.

The problem is intermittant - so it may be an intermittant capacitor - I
will replace it and let you know what happens. However because of the
DMM readout matching the specification so perfectly, I am pretty sure
this isn't the problem.

Does anyone out there know of a good reference for step down
transformers - specifications? I've heard of sams facts, but need to
know where I can purchase a copy.

TIA,

--Rob

 

[James Sweet]

Hi,

I've checked the capacitor - and the DMM readout matches the
specification - it's 100uF and it reads between 100 - 102 uF - perfect.
No signs of leakage that occurs sometimes in power supply caps over time.

The problem is intermittant - so it may be an intermittant capacitor - I
will replace it and let you know what happens. However because of the
DMM readout matching the specification so perfectly, I am pretty sure
this isn't the problem.

Does anyone out there know of a good reference for step down
transformers - specifications? I've heard of sams facts, but need to
know where I can purchase a copy.

You can't test electrolytic caps with a dmm, if at all in doubt, just
replace it as they're cheap.

 

[sofie]

n:
Your model of DMM may read the capacitance value BUT it will not give you an
indication of it's ESR value which is very important in many high frequency
circuits like SMPS power supplies.
If in doubt about the capacitor's condition, without an ESR meter to test
it, just replace the capacitor.... about $1.00 or less.

 

[n]

HI everyone,

Does anyone have a good web store for components? The capacitor I need
can't be found at my local electronics store (I"ve checked two places).
They had a 425V @ 100uF capacitor, but it was too big to fit into the
small LCD casing - about twice as large as the 400V, 100uF capacitor I
need. Any suggestions? I've been looking on the web to no avail so far.

Thanks,

--Rob

 

[[email protected]]

Does anyone have a good web store for components?

http://www.digikey.com/
http://www.mouser.com/

Also check the temperature rating of the capacitor - it will be printed
on it. 85 C and 105 C are the most common. Replace with one rated at
an equal or higher temperature.

Matt Roberds