BENQ 19inch FP937+ black display

[mildseven]

my 3,4 year old BenQ FP937+ 19inch display automatically turns black 2 seconds after turn on the switch. using my flash light, it's very dim but I can see my windows.
Funny thing is sometimes, it's working perfectly (whole day)
But most of time, once I turn on the switch, I see BENQ logo, and for 1 sec, I see my background of Windows, then it turns black.

After spent some time on searching, and I have decided to replace below items:
4 x Elite 470uF 35V cap with Rubycon
2 x Elite 1000uF 16V cap with Rubycon
2 x Elite 1000uF 10V cap with Rubycon
4 x 2SC5707
2 x FU9024N
1 x 3A fuse
before the replacement, I visually checked on caps but they seemed ok.
and tested transistor with my DMM, but didn't see they were shorted, but I gave a try.
however it ddin't fix the problem. what else do I need to check?
Thank you in advance for your help/suggestion

[Bobdee]

Re: BENQ 19inch FP937+ black display

my 3,4 year old BenQ FP937+ 19inch display automatically turns black 2 seconds after turn on the switch. using my flash light, it's very dim but I can see my windows.
Funny thing is sometimes, it's working perfectly (whole day)
But most of time, once I turn on the switch, I see BENQ logo, and for 1 sec, I see my background of Windows, then it turns black.

After spent some time on searching, and I have decided to replace below items:
4 x Elite 470uF 35V cap with Rubycon
2 x Elite 1000uF 16V cap with Rubycon
2 x Elite 1000uF 10V cap with Rubycon
4 x 2SC5707
2 x FU9024N
1 x 3A fuse
before the replacement, I visually checked on caps but they seemed ok.
and tested transistor with my DMM, but didn't see they were shorted, but I gave a try.
however it ddin't fix the problem. what else do I need to check?
Thank you in advance for your help/suggestion

This could be one or more bad CCFLs
But before going there you must resolder the 4 inverter transformers
Also check all the solder joints on the board with with a good 6 to 10 times magnifying glass looking for bad solder joints and ring cracks
Pay particular attention to anything on heatsinks
Then try again and post back with findings

[mildseven]

Re: BENQ 19inch FP937+ black display

Bobdee, thank you for your feed back.
I just resoldered 4 inverter transformers, and three heat sinks, but the same result

also I just did go through all the solder joints, but could not find anything is bad.

[Bobdee]

Re: BENQ 19inch FP937+ black display

Bobdee, thank you for your feed back.
I just resoldered 4 inverter transformers, and three heat sinks, but the same result

also I just did go through all the solder joints, but could not find anything is bad.

OK then just check 3a fuse and the 4 transistor that you replaced, because one or more may have blown again before you resolded the transformers, (sometimes and if not mostly the transformer ring cracks are the cause of fuse and a c5707 failing)
If they are still ok then you have to check the CCFLs

BTW I never meant you to resolder heatsinks themselves just components on them if they needed it

[Bobdee]

Re: BENQ 19inch FP937+ black display

Mildseven

you dont have to remove transistors to check them, check one pairs readings against the other pair (very rare both pairs go down)

[mildseven]

Re: BENQ 19inch FP937+ black display

I checked c5707, and fuse on board and seems fine with my Fluke DMM. (hopefully I test correctly..)

could it be 2 CCFLs are bad? When I turn the monitor on, I can see BENQ logos. if CCFL is bad, do you usually see the BENQ logo?

[Bobdee]

Re: BENQ 19inch FP937+ black display

I checked c5707, and fuse on board and seems fine with my Fluke DMM. (hopefully I test correctly..)

could it be 2 CCFLs are bad? When I turn the monitor on, I can see BENQ logos. if CCFL is bad, do you usually see the BENQ logo?

If you have one pair reading much lower than other pair then there is usualy a bad transistor in that lower reading pair, when that pair is removed you find that one is shorted
However more than probably now its bad CCFLs
As for seeing Benq logo yes you will still see it, you seem to have a failing tube or tubes that come on and the protection circuit senses that one or more is on its way out and it shuts down that is why it works sometimes, the tube is failing and close to dead if not dead now
There are a couple of ways to check CCFLs I personaly use another panel that has good CCFLs in it, some take panel apart and visibly inspect tubes
others have CCFL comp mod kit, and they use the inverter to test the monitor tubes and you can use the tubes to test the monitor inverter
Hopefully other members can suggest other methods to you

[mildseven]

Re: BENQ 19inch FP937+ black display

I think it's the bottom CCFL that's causing the problem. I was switching 4 pin to CCFL, and I removed top two pin to CCFL, then "BENQ" logo was dim.

but I have another problem, I have been resolding on the board, and now when I turn on the monitor switch, I dont have video signal. Green light changes to Amber after 1 sec.. where could be the problem? any suggestion?

[Bobdee]

Re: BENQ 19inch FP937+ black display

I think it's the bottom CCFL that's causing the problem. I was switching 4 pin to CCFL, and I removed top two pin to CCFL, then "BENQ" logo was dim.

but I have another problem, I have been resolding on the board, and now when I turn on the monitor switch, I dont have video signal. Green light changes to Amber after 1 sec.. where could be the problem? any suggestion?

Thats a nasty bit of bad luck
Check the whole solder side for any solder that might have spat about and created a short ect
Also check your solder work you may have bridged two tracks or something (with good magnifying glass)

[mildseven]

Re: BENQ 19inch FP937+ black display

Thanks, I'll get 10 times magnifying glass and take a look

[mildseven]

Re: BENQ 19inch FP937+ black display

Update:
It's working now!!
No signal sign was causing by faulty D-Sub cable.. It was working before, but somehow it's not sending any signal. I tested on other monitor, and it was giving the same error.
So I swaped with DVI cable, and now it's working. I dont know what was the root cause at the beginning. I still think my CCFL is getting old. I'll see if this happens again near future.
Thanks for all your help