macbook pro 820-2850 power cycle

[protocold]

I have a macbook pro A1286 2010 820-2850 logic board that power cycles every 5s. I can see from the PSU that it is drawing about 1A and then power cycle.

ALL_SYS_PWRGD cycles with it between 0v and 3.3v

PPVCORE_S0_CPU cycles between 0 and 1.1v

PLT_RESET_L is cycling between 0 - 1v

Is this fixable?

[piernov]

Re: macbook pro 820-2850 power cycle

History? C9560 replaced? BIOS flashed?

[protocold]

Re: macbook pro 820-2850 power cycle

board seems clean with no prior repair attempt, no dirty marks.

C9560 replaced and bios flashed, still the same.

[piernov]

Re: macbook pro 820-2850 power cycle

Same in SMC bypass mode?
Check voltage and resistance to ground on the GPU power rails.

[protocold]

Re: macbook pro 820-2850 power cycle

yes same in SMC bypass. In SMC bypass, fan spin high but still on and off pattern.

[protocold]

Re: macbook pro 820-2850 power cycle

PP1V05_S0GPU 0-1.04v pulses 295 ohm to ground

PP3V3_S0GPU 0-3.3v pulses 880 ohm to ground

PPVCORE_GPU 0-0.9v pulses 2.5 ohm to ground

PP1V8R1V55_S0GPU_ISNS_R 0-1.55v pulses 90ohm to ground

[protocold]

Re: macbook pro 820-2850 power cycle

@piernov what should i do next?

[magneh]

Re: macbook pro 820-2850 power cycle

Maybe check all the current sensing circuitry

could cause the shutdown

[protocold]

Re: macbook pro 820-2850 power cycle

thanks for your input, but could you possibly elaborate a bit as in where and where exactly i should look? I am a noob....

[protocold]

Re: macbook pro 820-2850 power cycle

Are you referring to the sensing circuit around ISL6259 (U7000) ??

pin 3 = 4v
pin 14 = 3.3v
pin 27-28 = 20.8ohm
pin 17-18 = 3.3ohm