820-2915 video distortion,but not the typical kind?

[roy.ruan]

having a 2011 a1286 with video issue.
there is very common video problem of this model ,usually we replace the GPU then it's done.

but this time is not that kind of typical ones that we deal with every day.
not the white screen can't boot into OS, shut down ,restarts. or the step by step vertical lines ones.... those are very common and replace the GPU will get the problem solved.


but lately we have two boards come in, exact same symptoms... there are some like points flashing and background is kind of red..definitely doesn't look like the GPU problems ones we seen before.
but anyway, we thought big chance was GPU , we replaced GPU on one of these two yesterday, turn on, exact same thing.

thought maybe the vram, we replaced all 4 of them, still the same thing.

so really not sure what's going on and can be the cause, definitely not the chipsets, theses are brand new 0001 we just bought and used on many others already.
we taped the MUX but no change at all

funny thing is that, both of their vram are HYNIX 1 G,not sure if it's related..


uploaded few pictures here and see if anyone has a clue?


thanks ahead!

 

[Gurmon]

Ah the reddish screen. I've got a couple in the workshop I have failed to fix so far. All these boards have already been re-furbed by Apple.

So far, just done basics, Replaced GPU, VRAM and reballed the mux. Made no difference what so ever. Laptop still fails the VST.

If I crack it, i'll report back here.

 

[TCRScircuit]

MUX may be bad? Reflow it

 

[dukefawks]

Still some issue with the frame buffer. Bad GPU/VRAM/soldering or knocked off/damaged component around the VRAM.
What date code 0001 chips are you using? You cannot just replace 0005 with 0001 or vice versa.

 

[roy.ruan]

Im using 1144, but for 1g boards, I had been doing this all the time like 2-3 months ago already.for all 1g vram boards with 6750, I replaced with 6770 and modify the resistors. all worked and system recognized the new GPU and run without any issues.

but the thing is that, the distorted video looks exactly the same after the replacement of GPU and Vrams , as when it came in(no works done to it) and it's not that kind of black label APPLE RMA board either..it's the regular ones with SN bar codes and numbers ones..

 

[roy.ruan]

same story here man,not sure, rumor says can be the PCB layers?

 

[MDY]

I have 2 boards here with same problem. I also replaced vram and gpu 2 times in all the same.

 

[roy.ruan]

right, i did the same thing already. really can't think of what else can be at this moment

 

[dukefawks]

Missing resistor or a trace problem in the PCB are all that is left.