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LCD monitor internal power supply repair

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.

Reply to
n
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Hi...

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

Ken

Reply to
Ken Weitzel

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

--

JANA _____

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.

Reply to
JANA

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

Reply to
n

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

Reply to
James Sweet

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.

-- Best Regards, Daniel Sofie Electronics Supply & Repair

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Reply to
sofie

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

Reply to
n

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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

Reply to
mroberds

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