Benq FP951 Invert/CCFL

[mdegan]

Hi,

After reading through the forum trying to find info on my faulty Benq FP951.

I have tried a couple of things.

My issue is no display, the power light stays on (Green).
If I shine a light at the screen I can make out a very faint image.

I have checked all the invert joins (all 22 of them, hope I'm looking at the right component) and replaced the 4 c5707's and the pico fuse.

Still the same issue, once it displayed an image for about 2 seconds and then back to nothing.

It has 4 individual CCFL tubes, if one has failed will it stop the rest from working?

Any help would be appreciated as I have not been able to find any info directly relating to the FP951.

Cheers
Michael

[Bobdee]

Re: Benq FP951 Invert/CCFL

Hi,

After reading through the forum trying to find info on my faulty Benq FP951.

I have tried a couple of things.

My issue is no display, the power light stays on (Green).
If I shine a light at the screen I can make out a very faint image.

I have checked all the invert joins (all 22 of them, hope I'm looking at the right component) and replaced the 4 c5707's and the pico fuse.

Still the same issue, once it displayed an image for about 2 seconds and then back to nothing.

It has 4 individual CCFL tubes, if one has failed will it stop the rest from working?

Any help would be appreciated as I have not been able to find any info directly relating to the FP951.

Cheers
Michael

Hello Michael
This is possibly a CCFL failure,as you suggested
If one fails then Inverter turns itself off
Have you resoldered the four Inverter Transformers??? (there is more than 22 joints between them)
Was the old fuse open???
Was there any shorts in old transistors???
Or did you just replace them hopeing it would fix problem (as it can do)

[mdegan]

Re: Benq FP951 Invert/CCFL

Hello Michael
This is possibly a CCFL failure,as you suggested
If one fails then Inverter turns itself off
Have you resoldered the four Inverter Transformers??? (there is more than 22 joints between them)
Was the old fuse open???
Was there any shorts in old transistors???
Or did you just replace them hopeing it would fix problem (as it can do)

Hi Bobdee,

Thanks for your reply, I just replaced all 4, hoping it would fix it.

There are only two inverter transformers on the board and each has 11 points.
To answer your question, no I have not yet I'm just about to start.

This is my first time doing anything like this it's only the second time I have used a soldering iron .

I'm not 100% on how to check if the fuse is open (I will search around now to find out)

Same answer to "was there any short on the old transistors", I;m not sure how to check just browsing youtube now look for a good how to.

[mdegan]

Re: Benq FP951 Invert/CCFL

Just checked fuse and both are closed. New and old one.

I tested with DMM in continuity mode and DMM beeped.

So I take it that means it's closed ??

[Bobdee]

Re: Benq FP951 Invert/CCFL

Just checked fuse and both are closed. New and old one.

I tested with DMM in continuity mode and DMM beeped.

So I take it that means it's closed ??

Correct
You can test your old transistors same way
Leg 1+2 1+3 2+3 But you should get no beeps on good ones
But my guess is they will be ok
So then you will need to get hold of a case mod kit to check your CCFLs

[mdegan]

Re: Benq FP951 Invert/CCFL

Correct
You can test your old transistors same way
Leg 1+2 1+3 2+3 But you should get no beeps on good ones
But my guess is they will be ok
So then you will need to get hold of a case mod kit to check your CCFLs

Just tested all 4 transistors and no beeps from any of them.

So next on the list, work out what/how to use a case mod kit to test CCFL's

Thanks for your help Bobdee!

[mdegan]

Re: Benq FP951 Invert/CCFL

Just had a thought, I can get my hands on the same model screen and do some part swapping.

Is there any chance I could damage the other working screen if I put the power/inverter board in it? I don't want to kill the other screen

[Bobdee]

Re: Benq FP951 Invert/CCFL

Just had a thought, I can get my hands on the same model screen and do some part swapping.

Is there any chance I could damage the other working screen if I put the power/inverter board in it? I don't want to kill the other screen

That sounds good but it looks like your Inverter is working (and possibly always have) so best left at moment
If you have screen with known working CCFLs at least one pair then disconnect a pair of top CCFLs connectors off your monitor and plug in a pair of CCFLs off the spare screen, power up and if they stay on then you have found problem, if they dont, try the same with bottom pair

[PlainBill]

Re: Benq FP951 Invert/CCFL

There should be no problem trying your power supply / inverter with another LCD panel. I am a little confused by your description of the problem, however.

A little background: The usual backlight design consists of an inverter and several CCFLs. The normal operating sequence is the monitor controller 'tells' the inverter controller to turn on the backlights (and how bright). The inverter controller drives the CCFLs to full brightness, then several seconds later begins monitoring the voltage across each CCFL and the current through each of them. If eithr voltage or current are too high or too low, the controller will shut down all CCFLs. There is no signal line to tell the monitor controller this has happened, so the power light stays green (or blue). This is the infamous 'two seconds to black problem.

You have already noted that a faint image can be seen. Another symptom is to turn the monitor off, then on again using the front power button. Usually each time you do this the backlights will come on for a few seconds.

There are three possible causes of this problem: A failure in the inverter drive system (bad transistors, open transformer, etc); a failure in the CCFLs (broken CCFL, 'worn out' CCFL, arcing in the wiring); or a failure in the monitoring components (open or shorted diode or transistor). One limitation of the case mod kit is the inverter doesn't monitor the voltage or current. Bobdee's suggestion for using the CCFLs in the other monitor is an excellent way to test.

PlainBill

[mdegan]

Re: Benq FP951 Invert/CCFL

That sounds good but it looks like your Inverter is working (and possibly always have) so best left at moment
If you have screen with known working CCFLs at least one pair then disconnect a pair of top CCFLs connectors off your monitor and plug in a pair of CCFLs off the spare screen, power up and if they stay on then you have found problem, if they dont, try the same with bottom pair

Inverter is working correctly.

I have removed the 2 sets of CCFL's and both look fine, no obvious defects.

Were is the best place to buy replacements?

I'm in Australia, in saying that I'm not fussed if they have to be shipped over just dont want to wait months for them to get here.

[Bobdee]

Re: Benq FP951 Invert/CCFL

Inverter is working correctly.

I have removed the 2 sets of CCFL's and both look fine, no obvious defects.

Were is the best place to buy replacements?

I'm in Australia, in saying that I'm not fussed if they have to be shipped over just dont want to wait months for them to get here.

You can run them out of the screen with care, then you can see what one is not working in the couple of seconds that they come on (bad ones can come on with a redish tint)
It has been known for them to have a faulty connection on the ends of some tubes (worth checking out on the bad one/s carefully)
Cant help you on where to buy as I have never had to buy them, I have plenty of non working screens stored for when I need them
Good Luck
Bob