Toshiba 20dl74 inverter problem

[dobber]

I picked up a Toshiba 20dl74 at the local recycling place along with my ususal stuff like laptops and monitors, I figured what the hell 10 bucks. I found that one side of the inverter was bad. It had a bad AO4077 Mosfet Chip on it, So I changed it out and the backlight lit up one time then when back out. So I checked the AO4077 and it burnt again. This is a very had Inverter to get ahold of at a good price so I have to repair it. I believe that the problem is after the Chip do to it lighting up once then burning out again. Is there any known suspect parts that may be causing a ground or overdraw on the chip? or anything that I should checking first? I will post a pic of the inverter as soon as I get home from work so you can see the parts on the board.

Thanks
Dobber

[cadiman]

Re: Toshiba 20dl74 inverter problem

One Inverter transformer shorted? Or is this a single transformer? Is the ao4077 on the power supply or inverter board?

You could check v and signal with mosfet out. Thats what I always do before replaceing burned ICs (look at spec sheet for that ic) Not sure about this model. There could be a problem with primary v going in (source or load) or secondary v out (source or load) that is taking out your mosfet.

Not sure if this helps. Good luck!

[ecking767]

Re: Toshiba 20dl74 inverter problem

Is there any known suspect parts that may be causing a ground or overdraw on the chip? or anything that I should checking first? I will post a pic of the inverter as soon as I get home from work so you can see the parts on the board.

Thanks
Dobber

I will check surround components like diodes and resistors. There could be a shorted resistor or diode for biasing that MOSFET.

ecking767

[dobber]

Re: Toshiba 20dl74 inverter problem

Ok, I will check out the suggestions and post my findings. I have not had time to work on the tv in a week due to having many Laptop repair jobs coming in this last week. I hope to get to in soon, Thanks Guys.