Macbook Pro PLT_RESET_L issue

[Francisco.s]

Hi! have an 820-3536-A, that PLT_RESET_L is not present. (0.0v)
All voltages for cpu are present, but cpu temperature is low. (about 35º c)
Fan is spinning and it rotates faster when left power-on for more than 60, 80 seconds, but cpu temperature keeps low.

Power consumption is also very low, no more than 350 mA.
As PLT_RESET_L is not present, there's no chime and no usb activity.

Voltages for cpu present and ok:

PPVCC_S0_CPU
PP1V05_S0
PP3V3_S0
PP3V3_SUS
PP3V3_S5
PP1V35_S3_CPUDDR

What signal (other than PLT_RESET_L) can make this mobo not work?

It is cpu damaged?
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[piernov]

Re: Macbook Pro PLT_RESET_L issue

https://logi.wiki/index.php/Bootup_S..._and_Broadwell

[Francisco.s]

Re: Macbook Pro PLT_RESET_L issue

Thanks piernov for this good piece of information.

I will estudie it an post new voltages and signals readings.

Best regards.

[Francisco.s]

Re: Macbook Pro PLT_RESET_L issue

I Have found the circuit that cause the problem.

Thanks to the diagrams in the excelente link, I could find that some signals feeds by the PP1V05_S0 rail, had no the correct level.

CPU_VIDSCLK signal reading was only 0.6 volts, and the pull-up resistance R7279 had 0.6 volts in both terminals, that confused me because one of R7279 terminals is connected to PP1V05_S0.

PP1V05_S0 was present in many points of the board, like in L7630, R7640 and many more, but in C1801 and some other components near it, voltage readings were almost half the voltage from PP1V05_S0.

Seems that resistance of PP1V05_S0 rail is not the well designed, because C1801 was in short-circuit, (lets say very low resistance) but not enough to activate the short-circuit protection of U7600.

Once C1801 capacitor was removed, the problem was solved and now there is chime and boots osx correctly.

Many thanks for your help.