hp 1908w monitor inverter problem

[zloi]

After first start monitor works few minutes (5 max) then brightness start to blink weaker-stronger,until light goes off completely.
when turn off and power on again monitor light is working only 3 sec.
All capacitor's have been removed and tested,all are good.
All tubes ave been tested with laptop inverter in two hours operation.all of them independently
All capacitor's have been changed with new one's.no change
Transformers have been removed,for secondary windings test.measured 625 ohm both.
On off signal is present and constant on qz9938 pin 10,
Brightness signal is present and constant on qz9938 pin 4.
All components in qz9938 circuit have been tested.
2kv capacitors are good.
during start light is operational until voltage on pin3 qz9938 reach's 2,26.
When pin 3 timer is shorted to the ground monitor is operational.but after first start 2-3 minutes later light start blinking as described.
turning off and powering again solves this problem and then it could work for hours.until now it has worked for at least 40 hrs total.
Brightness control is not working after shorting pin 3 to the ground.
Any idea what next is welcome.

[sam_sam_sam]

Re: hp 1908w monitor inverter problem

Welcome to this forum

Please show some photo of both side of all of your boards

For some one to help you

[alexanna]

Re: hp 1908w monitor inverter problem

After first start monitor works few minutes (5 max) then brightness start to blink weaker-stronger,until light goes off completely.
when turn off and power on again monitor light is working only 3 sec.
All capacitor's have been removed and tested,all are good.
All tubes ave been tested with laptop inverter in two hours operation.all of them independently
All capacitor's have been changed with new one's.no change
Transformers have been removed,for secondary windings test.measured 625 ohm both.
On off signal is present and constant on qz9938 pin 10,
Brightness signal is present and constant on qz9938 pin 4.
All components in qz9938 circuit have been tested.
2kv capacitors are good.
during start light is operational until voltage on pin3 qz9938 reach's 2,26.
When pin 3 timer is shorted to the ground monitor is operational.but after first start 2-3 minutes later light start blinking as described.
turning off and powering again solves this problem and then it could work for hours.until now it has worked for at least 40 hrs total.
Brightness control is not working after shorting pin 3 to the ground.
Any idea what next is welcome.

I have not had much luck testing backlights with an inverter ccfl tester.
When you are just powering on one ccfl you are not generating the same amount of heat that the pair being on would. Or there is a possibility voltage may be leaking to the other ccfls wiring, or several other explanations.
You have done a lot of testing, and have a lot of good information. I am just going to suggest something else to try.
This monitor is notorious for having insulation brake down at the return wire inside the panel particularly the top ccfls, I would strongly suspect when conditions get just right, voltage is finding an alternate path to ground inside the panel, causing the 2 sec to black problem.
I would start the testing over but this time substitute 2 known good ccfls for the top half and the original ccfls installed in the bottom half, don't forget to remove the jumper from the timing cap.. And then if need be move the test bulbs to the bottom.

[zloi]

Re: hp 1908w monitor inverter problem

Monitor is still operational.It's working few days for a at least 8 hours at day.
I will try suggested test.
After first post I tried powering on monitor without any lamp connected,Inverter powered and it was worked same,going off after 2-3 sec.
After that inverter power supply disconnected by removing l coil on +18v,under load 13,5v.
I was noticed,squealing sound from right top corner of panel,near by is t-connector board.Sounds like leaking voltage is this area,but this board is connected only with cable from video processing board
For this to be checked panel must opened.
Any suggestion or experience with this type of displays are welcome.
Anyone may feel free to leave comment.