Benq FP19G+ screen will not stay on

[Memran]

Hello! My first post here!

I have an old Benq FP19G+ screen and I have the following symptoms when I power on the display:

1. LED comes on green
2. After about 1 second, the purple BENQ splash screen is shown for about 1 second
3. Screen blanks for about 1 second
4. My windows desktop is displayed for about 1 second
5. Screen blanks, and stays blank.

If I turn off and back on, the same as the above happens every time.
If I disconnect the VGA cable (while power is still on) and reconnect, I see my windows desktop again, for 1 second, before the screen blanks.

After reading up on a few similar posts on here, I figured I'd take a peek inside...

Here is a pic of the board:



Here shows that some capacitors have pooped out some goo:


And underneath the caps:


I also spotted this one, which appears to have been cooked:


I have replaced all of the above, but there is no change to the symptoms described above. But at least I did not make it worse!

Is there anything else (simple / easy) that I can do to revive this, or is it time to dispose?

Thanks!

[selldoor]

Re: Benq FP19G+ screen will not stay on

Hi - welcome to the forum.
Some members do not like pictures posted in line- they may even pass over the thread
and go on to the next one. The Full Board pictures cannot be made big/clear enough for us to view for faults. Some Benq boards suffer from cold solder joints but cant really tell.
Have you cleaned the gloop off the boards- its sometimes becomes conductive.
Please post pictures jpgs no bigger than 2mb 2000x2000 using Manage attachments
which is found by clicking on Go advanced which is below Quck reply. Did you replace all the electrolytic caps? You may have 2 secs to black - read this from post 19
https://www.badcaps.net/forum/showthread.php?t=10419.
Can you see your desktop faintly when shining a bright light on the black screen?

[selldoor]

Re: Benq FP19G+ screen will not stay on

Forgot to ask, does LED stay on green after screen has gone black.
As you will read 2 sec to black can be caused by a number of things.
Next easy thing to check is resistances on the secondary windings of the Inverter transformers. This is covered in the guide and the result should be that both have a reading within 3% of each other. Meter on ohms 2000- Measure with power off and after its stood for 5 mins. post results. and part numbers of the transformers ( 2 rectangular blocks with yellow stripe around)

[Memran]

Re: Benq FP19G+ screen will not stay on

Thanks for replying. I've swapped the in-line images to attachments.

The green LED stays on, after screen blanks.
After more reading, I agree it is the "2 second to black" problem.

I've done some tests with the CCFL's. I believe they are in pairs on this screen. With the top two connected only, the display works for a second, as before, but with the bottom two connected only, the screen does not light up at all.

Looking at the circuit again, there appears to be a repeated section (transformer, cap, two ceramic caps, resistor) near the top two connectors for the CCFL's and also near the bottom two. One of the ceramic caps in the bottom section was the cooked one from the image above. (does that make sense?)

Will check inverter transformers next...

[Memran]

Re: Benq FP19G+ screen will not stay on

All but the large 450v 100uF cap replaced.

Both inverter transformers are reading the same.
Transformer part number: (Below is how it appears on a single one)
1J.26049.021
T2713B6427406

I want to test with the top two CC light things connected to the bottom two connectors, but the wires are not long enough, and I don't want to power up without the board being secure, and covered.

[Memran]

Re: Benq FP19G+ screen will not stay on

Forgot to answer: Yes, the screen is visible if I shine a torch onto it.

[selldoor]

Re: Benq FP19G+ screen will not stay on

Ok looks like bottom ccfls or wiring.
Read This https://www.badcaps.net/forum/showth...t=7900&page=17
from post 323 on.
It would really be ideal if you could get up the courage to test the set not in the case - Its not too difficult I set it up then switch on at the plug and watch what it does from a distance.
Pictures are better thanks - I would next go for resoldering the pins
on the inverter transformers. It is sometimes easier to get the old solder to melt if you
add a bit of new solder and flux. They are quite heavy connections so you
might want to warm the whole area with a hairdrier to give it a start.

[Memran]

Re: Benq FP19G+ screen will not stay on

I set it up as stated above.

When connecting the top CCLF's to the bottom connectors, there is nothing on screen at all.

When connecting the bottom CCLF's to the top connectors, I see the screen for a second, before blanking.

I conclude from this that all four CCLF's are working, but something in the bottom inverter circuit is not.

[Memran]

Re: Benq FP19G+ screen will not stay on

Success!


When I initially replaced the electrolytic capacitors, and the single cooked ceramic one, I made a schoolboy error!

The ceramic cap I put in was 15nF, not 15pF !! I have now replaced with the correct one, and the screen is fully operational!

Very big thanks for helping me with the diagnosis!

Mem

[selldoor]

Re: Benq FP19G+ screen will not stay on

Well Done!! another saved from the landfill.