Macbook Pro A1286 GPU issue - Fan spin 2 seconds

[simplylcd]

820-2915 MacBook - No screen / no boot / no chime just fans spins for about 2/3 seconds
I have already checked the following core voltages:
ppbus_g3h=12.5v
Dcin = 16v
pp3v42_g3h =3.4v
ppvrtc_g3h= 3.3v
PP5V_S5=5v
PP5V_SUS=5v
PP5V_S3=0v
When I short power on pads , fans spin then shuts down and pp5v_s3=5v for about 2 seconds then shutdown to 0v.
I removed L2406 so I could program the g-mux but the same thing was happening - on , fan spin , off
ppvcore_gpu diode = 0v
ppvcore_gpu = 4.5 ohms
Any tips would be useful.

[mon2]

Re: Macbook Pro A1286 GPU issue - Fan spin 2 seconds

Check the ENABLE pin - what is voltage value?

Check the output of this regulator -> what is the voltage value?

You may have a shorted cap at the output of this voltage regulator.

Respectively, power down (after checking the above); check the resistance on the output of this regulator / power rail to ground @ L7220 pin # 1.

What is the resistance reading?

See attached.

[dellxps15]

Re: Macbook Pro A1286 GPU issue - Fan spin 2 seconds

mainboard code ?

[MobileXT]

Re: Macbook Pro A1286 GPU issue - Fan spin 2 seconds

820-2915 known to have GPU failed. If the Video card is failed then there's nothing you do about it unless you can still able to boot into a single user then you can disabled the GPU.

[dellxps15]

Re: Macbook Pro A1286 GPU issue - Fan spin 2 seconds

if it's the 2011 version, and he write "I removed L2406 so I could program the g-mux but the same thing was happening - on , fan spin , off" he can make it run witout ati, but 2 fan spin mean something is wrong.

try remove the resistor R8911 that power on discrete vga and see if it still spin for 2 sseconds, or if it stay on , then u can program gmux.

[suiramix]

Re: Macbook Pro A1286 GPU issue - Fan spin 2 seconds

Hi there,
Any updates regarding this issue? I have exactly same model & symptoms!
There is gMux IC Bypass procedure by DosDude1 , does not require to remove L2406... just connect PLT_RESET_L to ground (see doslabelectronics. com /Demux). Do you want to share any .jed files? My guess is something else (beside GPU) is also defective (VRAM maybe) !

[suiramix]

Re: Macbook Pro A1286 GPU issue - Fan spin 2 seconds

An observation: just removing R9811 did not help much...same behavior (however there is 5.0V at one pin for 2 sec)... Simplylcd try to connect PLT_RESET_L from Pin 1 of R2881 to any GROUND and try again to program gmux IC...