Optiquest Q191wb turns white when off/standby

[mattbrad2]

I had a customer bring one of these in today that was blinking on and off. Usually a cap problem. Sure enough, opened it up and one 1000uf 25v was bulging. Replaced it and everything worked fine.. until the PC turns off or goes into standby then the screen slowly turns all white. I've attached the PS/Inverter board pics and have re-soldered the main fet and touched up any cold joints I saw. I've tested every cap on the board for a short. I know something is causing the inverters not to kick off but what exactly?

[alexanna]

Re: Optiquest Q191wb turns white when off/standby

I had a customer bring one of these in today that was blinking on and off. Usually a cap problem. Sure enough, opened it up and one 1000uf 25v was bulging. Replaced it and everything worked fine.. until the PC turns off or goes into standby then the screen slowly turns all white. I've attached the PS/Inverter board pics and have re-soldered the main fet and touched up any cold joints I saw. I've tested every cap on the board for a short. I know something is causing the inverters not to kick off but what exactly?

Depending on the circuitry, Usualy there is a problem with a shorted FET or transistor in the inverter area.Question, I have are all the backlights staying on or is it just one pair?
Ideally if you had some test CCFLs there were not inside a panel it would be easy to tell

[retiredcaps]

Re: Optiquest Q191wb turns white when off/standby

I've tested every cap on the board for a short.

1) Are those green caps Samxon GF? If yes, they are a known problematic series.

2) Capacitors die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

Most members here will recommend that you replace ALL capacitors with reputable brands from reputable sellers. Brands like Rubycon, Panasonic, and United Chemicon are suggested. A list of recommended caps can be found at

https://www.badcaps.net/forum/showthread.php?t=2280

[sabre504]

Re: Optiquest Q191wb turns white when off/standby

Similar if not the same board as used in the 17" Suyama
I changed all the caps and reflowed the transformer pins ,doing this solved the issue.
Looking at the picture you have uploaded one the 2 smaller caps near the
transformers looks bulged (150uf 25v i think on suyama)

[Rtech]

Re: Optiquest Q191wb turns white when off/standby

These need lots of re-soldering from the inverter transformers all the way to the lamp sockets.

[mattbrad2]

Re: Optiquest Q191wb turns white when off/standby

So this could still be a capacitor issue? I tested all the ceramic ones but no, since I don't have an ESR meter I usually don't test the electrolytic ones. I will try and replace the other ones and reflow the transformer pins and see what happens.

[mattbrad2]

Re: Optiquest Q191wb turns white when off/standby

Depending on the circuitry, Usualy there is a problem with a shorted FET or transistor in the inverter area.Question, I have are all the backlights staying on or is it just one pair?
Ideally if you had some test CCFLs there were not inside a panel it would be easy to tell

Tested using a spare CCFL - all 4 outputs are on.

[alexanna]

Re: Optiquest Q191wb turns white when off/standby

Tested using a spare CCFL - all 4 outputs are on.

Try disconnecting the logic board from the Inv/PS, see if the back lamps stay off

[Scenic]

Re: Optiquest Q191wb turns white when off/standby

^ if they stay off with the logicboard disconnected, the logicboard isn't switching the backlights off.
-> check the small transistors near the connector to the inverter/psu connector on the logicboard

[alexanna]

Re: Optiquest Q191wb turns white when off/standby

^ if they stay off with the logicboard disconnected, the logicboard isn't switching the backlights off.
-> check the small transistors near the connector to the inverter/psu connector on the logicboard

I am going to say that just a little bit different: if the back lights do not come on with the logic board disconnected them for some reason the logic board is asking that the back lights to be on. We would look at the logic board.
If the lamps remain on when the logic board is disconnected then we should look for a problem in the inverter area.
You also could try to identify the back on signal, and see if it goes changes from a high to a low voltage as the monitor goes into stand by.

[Scenic]

Re: Optiquest Q191wb turns white when off/standby

now that i re-read my post, it sounds more complicated than it is sorry..
shouldn't be posting in the middle of the night (4:06AM in post #9) after long and frustrating repair sessions

[alexanna]

Re: Optiquest Q191wb turns white when off/standby

I really think we said the same thing, I just added some more stuff