820-2779 - No backlight on LCD

[patrickribbsaeter]

CORRECT MOTHERBOARD NR:
820-2879
820-2879 - No backlight on LCD... Where should I start to measure?

1. Computer starts up. I have fan spin and chime. But no image! The screen is black, no apple logo when using light on the screen.
2. I have 12,6v on F9800 (for PPBUS_S0_LCDBKLT.
3. R9715 shows 180k, R9731 shows 200k.

 

[dukefawks]

There will never be backlight of there is no image. Voltage on C9010? Known good LCD assembly? Was this liquid?

 

[patrickribbsaeter]

No Title

There will never be backlight of there is no image. Voltage on C9010? Known good LCD assembly? Was this liquid?

U9000 Pin: 4 & 5 (Shows 0v).. Should be 3.4v. I think the IC is broken? On the otherside of the IC, i get correct volt.

 

[dukefawks]

I asked about C9010. If LCD is not recognized U9000 will never turn on either.

 

[patrickribbsaeter]

I asked about C9010. If LCD is not recognized U9000 will never turn on either.

Yes, sorry Duke..

The C9010: I get 27.5V..

 

[patrickribbsaeter]

Also: J900 (pin 4) on the LVDS connector shows 27.5V..

 

[dukefawks]

Look at schematic and tell me what voltage should be there. Pretty impossible to have 27V there and if it is really there then it is VERY bad.

 

[patrickribbsaeter]

Look at schematic and tell me what voltage should be there. Pretty impossible to have 27V there and if it is really there then it is VERY bad.

The voltage on C9010 shows 27v.. I have NO FAN spin now as well. Its gone. So where should I check first. Guess I need to trace everything back.. But where to start is FAN doesnt turn on? PPBUS_G3H..??

 

[dukefawks]

27V is not possible! Especially not when the fan is not even spinning. How are you measuring this?