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Either PSU or Darfon V144 inverter backlight problem?

Hello Guys,

I'm repairing a Haier L30CV6-A1 LCD TV and I can't decide if the problem is with the Darfon inverter or the PSU?

The problem is the backlight lights for 1 second then turns off. Having checked the transformers their respective windings are about 900 ohms and all the CCFL tubes are working.

The PSU seems ok, no bulging capacitors etc. However, the 24v line is reading 25.3v whether the inverter board is connected or not. I wouldn't have thought this would be a problem!?

Anyone got any ideas please? Any help appreciated!

Hope everyone has a good Christmas :-)

Thanks,

Ian - UK

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Hi, Please measure all windings again and see if there is one lower than 900ohm. All CCFL might seem working but only for one second before the protection circuit cuts in. By the way, there is something that I would like to know, what is the type number of your remote control?

Posted on Dec 31, 2008

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Got sound but no picture on my tv.


Hi.

First check if you have on screen menu and if the problem is still there if you change input source and cables.

If TV has no backlight on all inputs, then it is either inverter not supplying power to the backlight system, or the LCD panel itself. The inverter or the parts connected to the inverter are common cause for the problem. The LCD panel is not a common fault. When problem is the panel the TV is not worth repairing.

When there is an inverter problem the fault is not necessarily the inverter. The technician needs to test the parts to find out what part is responsible. Testing is done tracking voltage from PSU to inverter. Voltage to inverter is usually supplied by the higher VDC line from PSU. Here broad description of how to test the three parts: Before proceeding...

Here replacement parts for most flat panel TV models:ShopJimmy.

See also:
PartStore

Regards.

Ginko.

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1 Answer

Philips 32pf9641d/10 fault works well for 90 mins then goes black still images on screen but no backlight ? power supply or inverters? if inverters can they be repaired or replacement only,


Hi.

As you said when there is no backlight the problem is either inverter or power board. In some case the main controller board may be responsible.
You need to test the parts to find out what part is responsible. Testing is done tracking voltage from PSU to inverter. Voltage to inverter is usually supplied by the higher VDC line from PSU. Here broad description of how to test the three parts: Before proceeding...
The TV can be repaired at component level or replacing boards, depending on your skills and experience. If you want to repair at component level, after diagnosing the faulty board you test components and circuits individually. In that case to test inverter in full you will need an oscilloscope to read the phase of inverter AC section (oscillators or IC must be tested).

Note: If Inverter has voltage out to CCF lamps, then the parts mentioned above are OK, in that case you have a faulty LCD panel. The TV is usually not worth repair as the LCD panel is expensive. LCD panel faults are not common.

Here replacement parts for most flat panel TV models:ShopJimmy.

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1 Answer

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Hi.

Problem is inverter, backlight or PSU. The backlight lamps that illuminate the LCD display are flashing. This creates the "kind of strobe" effect that you see. There are several possible causes for the problem.

The lamps themselves are defective. The lamps do not fire up completely and keep flashing. The lamps are not sold alone but they are part of the LCD display. If the lamps are gone the TV is not worth repairing.

The inverter is the high voltage board that supplies the backlight lamps. If the inverter is defective it can still be replaced. Testing is done reading DC in, checking high voltage out, and using an oscillator to test the phase of the AC out signal generated by the inverter oscillator section.

PSU or main controllers may be defective. This will less common in case of flashing back-light. Test this if the inverter is OK and if the problem is DC voltage input to inverter.

Here parts: 42LA30H - ShopJimmy

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Ginko

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change the lamps unit will work fine.
regards,
daniel

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I would recomend replacing the 11 caps on the inverter as 90% of the time its failed capacitors on the inverter. If you shine a bright light into the screen can you see the pic? Thats usually one of the first things I do when I suspect bad caps on the inverter.

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