820-00138 graphic issues

[DentingDave]

Hi guys,
Got a A1398 , board 820-00138.
It boots in different ways with different issues randomly.
- Chime but no image no backlight.
- Loop on Chime sound (no image no backlight)
- Boot with wrong colors and wrong resolution
- Boot normally and suddenly screen came black , but backlight stays on. (after a few seconds during boot , or after 10-15 minutes of normal use with no issues).

No liquid damage boards looks perfect.
Tried to disconnect everything... replaced display & ssd without improvements.
Apple hardware test gave back a possible display problem only one time.
Any suggestions?

Thanks!

 

[2informaticos]

If there is only iGPU, should be CPU, or RAM issue.
On external monitor get the same video problems?

 

[DentingDave]

Yes same problems on external display.
Is there a way to virtually remove a single bank of RAM? (like removing a resistor on power line for example)...

 

[2informaticos]

I don't think.
Try to reflow all RAM chips.
But your problem could be CPU itself.
However, if you plan to work on this board, start changing the f**g FDMF6808 chips with new FDMF6708.
I don't think to be the problem which generates the actual symptom.
But you can test again after changed them; before of any RAM/CPU reflow.

 

[DentingDave]

Ok so I'll change all the three fdmf6708 before doin' anything else. In fact, I also already tried the script that keep the CPU busy Just to test if the problem could be related to the fdmf... But nothing changed.

??????But ok I'll give It a try and i'll go for that.

Thanks a lot man!