820-00292 video issues

[Kyle93]

This arrived turning on with fan spin but no led light #3. Most likely thought it was the GPU after replacing the 3V battery and pram reset.

Using a replacement tested 820-00292 board, all leds come on, you can hear chime but only backlight appears on internal LCD. External video works fine.

Is it possible the original board with no led#3 coming on also internally damaged the LCD? Customer claims the iMac just randomly died.

 

[2informaticos]

I don't think LCD got damaged because of MLB.
Didn't test it after PRAM reset?

In the repair process, you can let CMOS battery out.
Then MLB should boot automatically, when power is applied.

 

[Kyle93]

Same issue after PRAM reset and CMOS battery removed.

What should be tried next?

 

[2informaticos]

Which schematic are you using in the repair process?
Check voltage on all big coils.

 

[Kyle93]

Solved. Found another screen in the shop with a crack in it for testing purposes and now have internal image.. For future reference, looks like it is possible after all for the MLB to damage the LCD since this was never opened up prior.