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LCD TV won't turn on, Screen and Standby light blink

I have a 37'' Magnavox LCD TV (Model # - 37MF231D/37) about two weeks ago the standby light started flashing when you went to turn it on and then it would come on about 5 minutes later. Now it has gotten to the point where it doesn't come on at all. When you push the on button the standby light flashes and the screen dimly flashes light. This will go on for hours without the TV actually turning on.

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  • hammbone76 Mar 30, 2009

    I have a similar problem with my Sony Bravia KLV-40U100m flat screen LCD TV. My TV won't power up AT ALL. No flashing lights, no steady lights. I am getting 120V to the power board, I've only found 2 fuses, and both are good on the power board, but no power is getting to the video board. Heard of this? Any fix without having to replace the entire board? I've trying to figure out the common problem... seems that alot of folks that bought this TV have the same symptoms...

    Thank you!

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This sounds like the flyback unit on the main board is burnt out! replace and you should be fine!

Posted on Dec 12, 2008

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I had a similar problem which I have partially solved. The power light flashing could be due to a shorted electrolytic on the power supply board but in my case it was a shorted IC on the main board, the one with the input connectors. The IC marked 7001 shorted and got hot enough to melt the plastic. Replaced it with a new one from Mouser. The supply measured on the end of inductor 5001 farthest from the IC reads 12V now. This is a surface mount part and has a pad on the bottom that may be soldered to a pad under it. I had to cut the IC apart carefully with a Dremel cutoff wheel to remove it. That fixed the problem with the light and the remote now turns the TV on and off so the logic is working.

I now have the problem of the backlight not turning on. The driver board, the ones with the transformers, are made by Intechwave, the only info I can find is here: http://www.peopleworks.co.kr/kor/product/product_list.php?intDivision=4&intClass1=16&intClass2=41

This a 45kHz RF driver and it is not starting. If I can figure out why I'll post it for all the people who reported slow or no turn on of the backlight. These boards should have 24V between the red wires on the connectors and ground, as mine do.

Posted on Jan 27, 2009

  • pcberkebile Jan 27, 2009

    Correcting my last entry the IC isnumbered 7003.

  • pcberkebile Feb 21, 2009

    I have gotten my set working (the backlight) although not exactly by fixing the original circuit, I'll explain at the end.

    I traced out the circuit that operates the backlight and it works like this.
    1. The backlight is powered by two similar looking boards, one on each side of the chassis. You can identify them by the windows above the transformers. These boards operate on 24VDC that comes in on the red wires, black is ground. There is also an on/off line, a logic level around 5V turns the lights on.

    2. Power for the lights comes from the main power supply board. If you follow the wires from the connectors back to the power supply you will find that they connect to two identical connectors on the board.

    3. Near to these connectors is a TO220 power FET, it is the power switch that applies the 24V to the backlight. The FET is connected as a source follower and when a turn-on signal is received from the logic its gate is pulled up several volts above 24V and applies 24V power to the backlight boards.

    4. The turn-on signal comes from circuitry toward the other side of the board. There is a 220K leaded resistornot far from the TO220 FET. When the backlight is off I measure 16.2 Volts on one end of this resistor and almost zero on the other end. When the backlight is on I measure 34.5 on one end and 27.2 on the other (the 27.2 is probably the result of my fix and probably should be higher). It is this 27.2 volts that turns the FET on and applies 24V to the display.

    5. The current from the 27.2 volts (about 20 uA) is applied, through a 12V zener that is located between the TO220 and the backlight board connectors, to a couple of transistors that form the switch for on/off /ine to the backlight board. These transistors are numbered 7077 (pnp) and 7078 (npn), the emitter of the npn is connected to the on/off line and I measure 3.7 volts when the display is on.

    I was not getting the necessary voltage to turn the power or the on/off line on, some of the current through the 220K resistor was getting diverted somewhere. I replaced a few suspect components and when that didn't fix it I realized that I was doing too much damage to the board (run seperation)
    so I quit trying to find the bad component and invented my own fix, a two-transistor regenerative switch that replaced the 12V zener. The set now works and has been working for a few weeks.

    I am reluctant to post the details of my fix on a forum like this, if you would like the information let me know how to get it to you privately.

    Incidentally the power to the power supply board is never turned off, the 24V and a second supply that I think is 12V, I didn't write it down, are always on before the transistor switches on the power supply board. You can measure these on the + side of the electrolytics.



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