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Equipment Repairs => LCD TV forum => Topic started by: dfsa89 on December 26, 2011,04:28:31

Title: Memorex MLT1921 backlight auto off
Post by: dfsa89 on December 26, 2011,04:28:31

Hello all,

I have a generic memorex lcd tv. The backlight cuts off within a minute. There are four ccfl, two on the top and two on the bottom. The top two both lights up red/violet and fades to white (bad tubes).

Does having bad tubes normally cause other tubes to cut off?

A picture of the power/inverter board is attached.
Proview Technology Co., LTD
PI-XXXXTLTX Version:B
200-001-XXXXTLTX-BH

860-AB0-190DTLTD-1H

Any help or info is appreciated.

Thanks.

Title: Re: Memorex MLT1921 backlight auto off
Post by: ProDave on December 26, 2011,05:19:07

failing tubes is your problem.

Tell us what IC's are used on the inverter, there may be some tricks to stop them cutting out.

Title: Re: Memorex MLT1921 backlight auto off
Post by: billy no mates on December 26, 2011,05:20:47

hi
yes ive read in some other post somewhere that bad ccfls can cause it to go off
and a pinky/red tint usually does mean that the ccfl is getting duff
..looking at the capacitors in your pic they dont look bulged but that doenst mean they are'nt faulty


hope this helps
billy

Title: Re: Memorex MLT1921 backlight auto off
Post by: dfsa89 on December 26, 2011,07:28:51

Thanks for the replies.

Texas Instrument TL494C seems to be it.
Is there any temporary bypass for this ic to test for other possible faults?

The two 8 leg in the picture above is a 4511GD.

Thanks again!

Edit: I have ordered some new tubes.
Edit2: New tubes works fine. Thanks for the help

Title: Re: Memorex MLT1921 backlight auto off
Post by: ProDave on December 28, 2011,11:39:00

Can you do some legwork and find a circuit diagram?

There's no simple way to disable protection on this chip, but sometime you can remove a feedback diode to prevent the chip sensing a duff tube, but I couldn't even begin to guess at which diode to remove without a circuit diagram for the inverter board.

Title: Re: Memorex MLT1921 backlight auto off
Post by: Turnip on December 29, 2011,10:35:26

Hi,

Never found any permanent cure for the bright red start-up biz apart from tube change.

Guess someone will know where the red comes from. Thought  - Mercury-blueish, Copper-green, Red -Iron - wonder what cold cathodes are made from when coating oxides are burnt to the nub - probably wrong but keen for info - Chris