Compaq A900 (JBW00 LA-3981P) Schematic

[speedypro]

Hi

I'm working on this Compaq A900, it has no backlight. Inverter and cable ok. Anyone got any schematics so I can troubleshoot?

Thanks

[alihomee]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

how u check the inverter and cable .you can do this one without waiting for schematic.check 15-18v alw on inverter jeck while you plug in the adapter and also check 5v when the display appears

[spidey]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

here

[speedypro]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

how u check the inverter and cable .you can do this one without waiting for schematic.check 15-18v alw on inverter jeck while you plug in the adapter and also check 5v when the display appears

No point since Ive tried other known working cable and inverter. I'll use schematic.

[speedypro]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

Nothing on the schematic can give me a clear answer why no backlight. Anyone faced similar issue?

Edit:

I think U18 (KB926QFB1) is damaged. Could I use any off other boards?

[spidey]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

all answers on page 17; check INVPWR_B+(pins 1,3) , INV_PWM (pin 28), DISPLAYOFF#(pin 30).

[speedypro]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

all answers on page 17; check INVPWR_B+(pins 1,3) , INV_PWM (pin 28), DISPLAYOFF#(pin 30).

19v+ on INVPWR_B+ but nothing on INVPWR_B. This, to me, points at U18. Am I correct?

[spidey]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

you can wire 3.3v from nearest place you find on the board(remove pin28 connection). btw how about pin30 ?

[alihomee]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

inverter needs 12v-19v and 5v-3v and ground to turn on 19v present always and 3v comes with display so check all the points of your inverter if some thing is missing means ur cable or mobo can have problem

[speedypro]

Re: Compaq A900 (JBW00 LA-3981P) Schematic

inverter needs 12v-19v and 5v-3v and ground to turn on 19v present always and 3v comes with display so check all the points of your inverter if some thing is missing means ur cable or mobo can have problem

I have changed cable + inverter and same issue. But thanks for your kind support.

To wrap this up, I have replaced KB926QFB1 and backlight now works. This means I have many boards with this same issue. Took long to get this IC back on the board lol. But hey, this post has been solved. Thanks all!