Dell E172 Power board

[mrtweaver]

I did a search on here and found several threads regarding this power board. However none of them seemed to be the problem I am having. I know it has to do with the HIGH power side. See attached photo of board.

The area that is circled in red is the problem area. Right now I have the line side of both transformers connected. The load side of the top transformer is not connected. If I connect both load sides of both transformers, it shorts out the two transistors located just beneath the two transformers.

The bottom side has no problems, except for the fact that when powered on the CCFL will only light for about 3 to 5 seconds then turn off.

I have built a CCFL tester and have tested all 4 lamps in the monitor and they all function well. I also tested the output of the power board and it is ok during that short period when it is on.

I have went through and checked the diodes, the resistors, the FET's, the caps, and can not find anything else that could be causing the problem. I even on a hunch just replaced a bunch of the components.

There has to be something that commons the two transformers, that causes the higher load on the transistors which causes them to fail. But I am right now at a loss.

Any help greatly appreciated.

When the transistors in question short out, it causes the power light to flash.

Thanks for looking.

[ratdude747]

Re: Dell E172 Power board

If you haven't already, resolder all 4 inverter transformers. Bad transformer soldering is the root cause of the transistor failures and until the bad soldering is fixed the replacement transistors will fail very quickly.

[budm]

Re: Dell E172 Power board

I second that on ratdude comment, also check the PF781 3A black fuse by the cap, make sure the resistance is less tahn 1 Ohm, this fuse when it is bad will have about 3~5 Ohms resistance. Also check the 4 yellow tuning caps by the 4 transistors, make sure hey do not have resistance leakage and corect value, if these caps are bad the Royer Oscillators for this inverter driver transistors will burn up.

[selldoor]

Re: Dell E172 Power board

Have you tested the secondary wiring resistance on both inverter transformers.
What transistors are you using?