Apple macbook a1278 820-2936 need some help

[piernov]

Re: Apple macbook a1278 820-2936 need some help

Exact same behaviour: PLTRST# present but not POSTing? No beeps without RAM?
No oscilloscope to check activity on BIOS CS# or LFRAME#?
Tried yet another BIOS?
Could still be (in order or probability and easiest to replace) SMC, PCH or CPU.
Or some random missing/corroded resistor, so be sure to go through the whole board under the microscope to spot anything wrong.

[justin35]

Re: Apple macbook a1278 820-2936 need some help

Well i came back over this board...
Oscilloscope on bios chip
Pins 1,5,6 only a spike of data (with ram or without ram installed)
On an working board i have the same behavior without ram. With ram installed i have more activity then just a spike.
My problem is isolate_cpu_mem_l which comes high for a split of second...
On page 30 of schematic where it explains states of the machine, for s0 state all _L lines must be high, including isolate_cpu_mem_l
I don’t know what to do next... i don’t understand 100% that part of schematic (q3020, q3015, etc)

Thanks!

[pateldee@live.co.uk]

Re: Apple macbook a1278 820-2936 need some help

Hi there,

I have the exact same issue and been trying to figure this out for ages, any luck? My cpu vcore is stuck at 1.15V, is it possible it is the PCH even tho its partly working? or even cpu even tho its able to request its own voltage for vcore?

Any solutiuons anyone would be a great help..

Kind Regards
Dee

[Christo_venom]

Re: Apple macbook a1278 820-2936 need some help

i have 820-2936-B with the same problems:

i have green light, fan spin gradual spin up to full speed.

i dont have PPVCORE_S0 (I JUST READ THAT won'tcome up until internal screen is connected)

[piernov]

Re: Apple macbook a1278 820-2936 need some help

i dont have PPVCORE_S0 (I JUST READ THAT won’tcome up until internal screen is connected)

PPVCORE_S0_CPU has to be present regardless of the screen being connected or not.
If ALL_SYS_PWRGD is present but PPVCORE_S0_CPU is missing, one possible issue on this board is TON resistor R7402.