BENQ FP91G+ problem

[simke]

I have problem with BENQ FP91G+ lcd monitor.Monitor won't to power up.
When I plug in power cord in monitor I hear quiet whistling from back of the monitor,when i press power button on monitor whistling stops,screen is on for a moment with Benq logo and then turn off.Any help would be much appreciated.Thanks.

[Davi.p]

Re: BENQ FP91G+ problem

Is a well known fault, search the forum for the keys "Benq FP71g" or "C5707"

[selldoor]

Re: BENQ FP91G+ problem

or just "FP91G"
see here
https://www.badcaps.net/forum/showth...ighlight=FP91g

[budm]

Re: BENQ FP91G+ problem

Check the C5707 transistors, solder joints on the transistors and inverter transformers. Check the black fuse PFxxx, it should be less than 1 Ohm.

[mejohn]

Re: BENQ FP91G+ problem

I got a very similar problem and exactly the same board! If I switch the monitor on, the green led lights up and for a fraction of a second I see the blue benq label on the monitor. Then the monitor is dead again.
I already checked the black fuse PF801 and the LDO regulator on the logic board, there I measured to voltages 3.3V and 1.8V.
I couldn't find the C5707, please give me a hint. The capacitors all look very good, none is curved or vented.

[budm]

Re: BENQ FP91G+ problem

Just to be sure, you need to upload good clear pictures of YOUR board for us to look at.

[mejohn]

Re: BENQ FP91G+ problem

Just to be sure, you need to upload good clear pictures of YOUR board for us to look at.

Here you are. If you want specific pictures, please don't hesitate to ask.

[budm]

Re: BENQ FP91G+ problem

"I couldn't find the C5707"
Q808, 809, 815, 816.
These boards are know for having lots of bad solder joints in the inverter section (transformer legs, transistor legs, cap legs etc), and bad tuning caps (grey rectangular caps, lose its capacitance).

[Lumberjack777]

Re: BENQ FP91G+ problem

If I might add budm - I'd also check Q812 & Q805. I've had one of them go on occassion.

And resolder those transformer legs etc, as budm said, or it will happen again.

Here's a typical repair kit for similar models. http://www.ebay.com/itm/REPAIR-KIT-E...item54042beafc

[mejohn]

Re: BENQ FP91G+ problem

I checked all components including the mosfets (Q805, Q812) and found that two C5707 are gone (Q808 and Q809). In approximately 4-6 weeks I get the parts from china and I am going to post the result.

Thank you very much!

[mejohn]

Re: BENQ FP91G+ problem

Success! After replacing the two faulty c5706 and resoldering a lot of legs the monitor works fine again.