Green light, not turning on. missing voltage rails


I have started working on an old obsoleted board again.

It is the A1229 model

This machine does not auto power on so I plugged in charger and touched the power on pads with tweezers and got green light

The fan spins and stops, It keep on doing this

I get 5v on pin 1 on u7300, which is PP5V_S5

I have 4.9v on PP5V_S5, I checked on c8900 to confirm

I checked all_sys_pwrgd, on Pin 4 of u7880 and get 3.2v

On c1252 which is PPVCORE_S0_CPU i get 0,7v

If I keep My probe on c1252 and when the fan starts I get 0.7v but then when fan stops the voltage goes down to 0v but when fan starts spinning again the voltage goes to 0.7v

This just loops

I then started testing resistors surrounding u7900 (ISL6255AHRZ)

I have checked R7905  which is 18.1 ohm

R7906 is 2.4 ohms

R7904 is 000.2 ohms

I cant see anything wrong visually

Update (09/24/2020)

the board is 820-2132-a

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can anyone help me please

that is knowledgeable in board repair

Thanks so much in advance


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