820 2915

[Anterweb]

This is driving me nuts dude!

Came in with classic faulty amd GPU, and a crack in the glass of the screen( Screen still worked fine but glass cracked )

Removed R8911 and killed gpu with medusa and set an EFI password all worked great so set about changing the screen .

Put on what I had marked up as a good know screen fit it mac turns on but I get no screen output at all, Presume display is bad and try another as I have a pile of them, same thing on 3 different LCD panels. I then put back original screen with cracked glass same result, Powers on I hear a chime fan spin but no display!

( Im concerned that while rushing to get this job done I may have forgotten to disconnect the battery when removing LCD ribbon! )
Tried Pram reset with medusa and re applying AMD disable same problem,.

Also cant try external display due to medusa killing AMD chip.,

What would be the next step in fault finding this please?

 

[2informaticos]

Need to post some voltage and signals on the LVDS connector.
Check pins 3, 4, 6, 7; LCD connected, of course.
Be sure no knocked off components, or broken traces near J9000.

 

[Anterweb]

3 - 0v
4 - 3.3v
6 - 3.26v
7 - 3,26v

I followed pin 3 back on the board all the way to R9678, where i get

GMUX_S3_PD_GND = 2.67v
LCD_PWR_EN = 11.9mV

Bit stuck now?

 

[2informaticos]

Did you measure with LCD connected?
Did you test known good LCD assembly?

 

[Anterweb]

Yes and yes

 

[2informaticos]

Did you get any kind of image with GPU enabled?
If yes, put back R8911 and flash backup BIOS.
Let see what happens.

 

[Anterweb]

Ive only got bios files for this with GPU disabled., Can I just reset pram to reverse medusa gpu disable? Im sure there is a medusa setting to force pram reset.

 

[2informaticos]

"Ive only got bios files for this with GPU disabled"
I was talking about original BIOS, if that gave some image at beggining.
Didn't make backup???

 

[Anterweb]

OK, as I do so many of these identical macs the 2915, ( my wife is a school teacher and they have hundreds of these in her school so I'm always getting asked to repair them.)

I did have a backup bios, put back R8911 and got image with original screen,

Re flashed bios removed R8911 all good. Used a different new screen and its all fixed.

Not sure what happened on this one but its working sweet now. Thanks for your helps bro