820-3332-A power cycling

[air_chair256]

hi everyone

i have a Macbook pro 2012 820-3332_A came in as water damage device, it used to turn on with no keyboard connected so we replaced keyboard and it worked for awhile and then it stopped working, it shows green/orange light and fan spins for a second then stops then spin again and stops and keeps repeating, some voltages are pulsing such as CPU Vcore the voltage goes to 1V then drop to 0V, GPU voltage is always 0V, i got another motherboard that is fully working and nothing wrong with it i put it in the same case ( water damaged case) and once i connected all cables this motherboard stopped turning on and started doing the same behaviour and power cycling so i removed all cables except the speaker so it started working and i heard it chime so i tried to only connect J4400 and it turns on fine then i unplugged the charger and connected J5100 (Trackpad), J6701 (Mic/headphone) and J5815 (Keyboard Backlight) and once i turned it on it started to power cycle and i unplugged all the cables but no change so now both my boards are power cycling but i only want to fix the second board because it was working fine and then stopped working so one of the cables must be defective and shorted the motherboard so i believe it would be easier fix. i had a look at the board and i found C7511 Pin 2 was burnt badly and brown so i removed the cap and checked with diode mode and it shows 0,001 and with ohm mode it shows 1.6 ohm so i think it's shorted? i tried to remove Q7510, Q7515, Q7550, Q7551, and it's still the same,

Power rails

PPBUS_G3H: 12.58V Stable

PPVIN_S5_HS_COMPUTING_ISNS: 12.58V Stable

PPVIN_S5_HS_GPU_ISNS : 12.58V Stable

PPVIN_S5_HS_OTHER_ISNS: 12.58V Stable

PPDCIN_G3H: 16.80V Stable

PPDCIN_G3H_ISOL: 16.80V Stable

PP3V42_G3H: 3.397V Stable

PPVRTC_G3H: 3.3V Stable

PP5V_S5: 5V Stable

PP5V_SUS: 5V Stable

PP5V_S4: 5V Stable

PP5V_S3: 0V

PP5V_S0: 5V dropes to 0.2V Pulsing

PP3V3_S4: 3.3V dropes to 0.2V Pulsing

PP3V3_SUS: 3.3V Stable

PP3V3_S5: 3.29V Stable

PP3V3_S3: 3.3V dtopes to 0.3V Pulsing

PP3V3_S0: 3.3V dropes to 0.1V Pulsing

PP3V3_TBTLC: 3.3V dropes to 0.2V Pulsing

PP1V05_TBTLC: 1V dropes to 0V Pulsing

PP1V05_TBTCIO: 1V dropes to 0V Pulsing

PP15V_TBT: 2.4V dropes to 1V Pulsing

PP1V8_S0: 1.8V dropes to 0V pulsing

PP1V8_S0_CPU_VCCPLL_R: 1.8V dropes to 0V Pulsing

PP1V5R1V35_MEM: 1.3V dropes to 0V Pulsing

PP1V5_S3RS0_CPUDDR: 1.3V dropes to 0V Pulsing

PP1V5_S0: 1.5V dropes to 0V Pulsing

PP1V5_S0_RIO: 1.5V dropes to 0V Pulsing

PPVTTDDR_S3: 0.6V dropes to 0V Pulsing

PP0V75_S0_DDRVTT: 0.6V dropes to 0V Pulsing

PP1V05_SUS: 1V Stable

PP1V05_S0: 1V Stable

PP1V05_PCHVCCIO_S0: 1V Stable

PP3V3_S0GPU: 3.3V dropes to 0.1V Pulsing

PP3V3_S0GPU_MISC:3.3V dropes to 0.6V Pulsing

P1V8GPU_EN: 3.3V dropes to 0V Pulsing

PP1V5R1V35_S0GPU: 1.5V dropes to 0V Pulsing

TP_GPU_PGOOD2: 1.4V dropes to 0.1V Pulsing

PP1V0_S0GPU_ISNS: 1V dropes to 0V Pulsing

PPVCORE_GPU: 0.8V dropes to 0V Pulsing

PPVCORE_S0_CPU: 1.1V dropes to 0.9V dropes to 0V Pulsing

PPVCORE_S0_AXG : 0V

PP1V5_S3_CPU_VCCDQ : 1.3V dropes to 0V Pulsing

PP1V05_S0_CPU_VCCPQE: 1V dropes to 0V Pulsing

PPVCCSA_S0_REG: 1.05V dropes to 0V Pulsing


any help would be appreciated.

 

[2informaticos]

"checked with diode mode and it shows 0,001 and with ohm mode it shows 1.6 ohm so i think it's shorted?"
Do you mean between cap pins, or L7510 to ground?
VCORE has low value to ground as normal.
I hope you didn't power on the board without C7511; also check R7511 integrity.

"i tried to only connect J4400 and it turns on fine then i unplugged the charger and connected J5100 (Trackpad), J6701 (Mic/headphone) and J5815 (Keyboard Backlight) and once i turned it on it started to power cycle"
Only trackpad can cause that symptom from these connections.

Did you try SMC bypass mode?

 

[air_chair256]

thanks for your reply

"checked with diode mode and it shows 0,001 and with ohm mode it shows 1.6 ohm so i think it's shorted?"
Do you mean between cap pins, or L7510 to ground?
L7510 to ground

I hope you didn't power on the board without C7511; also check R7511 integrity.
i tested R7511 and it seems ok, i used beep mode and put each prob on one side and it beeped
and unfortunately i did try to turn it on without C7511


Did you try SMC bypass mode?
yes i tried to turn it on by holding the power button continuously and it still power cycling and the fan spins and stops but it spin faster

 

[2informaticos]

"unfortunately i did try to turn it on without C7511"
Do NOT do it again.
You are very lucky if Q7510 is not shorted now.

"PP5V_S3: 0V"
Are you really sure?
It MUST pulse at least, if you get pulses on other S3, even S0 voltages...

 

[air_chair256]

"unfortunately i did try to turn it on without C7511"
Do NOT do it again.
You are very lucky if Q7510 is not shorted now.
i think L7510 is shorted to ground since i get 1.6 ohm? i soldered Q7510, Q7515, Q7550, Q7551 back on the motherboard, are they should i remove them again and check the line to see if the short goes away?

"PP5V_S3: 0V"
Are you really sure?
It MUST pulse at least, if you get pulses on other S3, even S0 voltages...

sorry i was measuring on CD001 pin 1 and i got 0V but i just checked on C7300 and i got 5V

 

[2informaticos]

"i think L7510 is shorted to ground since i get 1.6 ohm"
That could be normal value for VCORE; compare with similar board...

 

[air_chair256]

yes i compared and it's the same. i noticed U1800 gets warm, but i think it's normal? where should i start looking or testing?
is there anyway to check to see if U7400 is functioning? since C7511 was burnt the U7400 can be shorted. i tried to remove U7400 and turned the motherboard on and the fan started spinning and didn't stop or power cycled but it can be because no cpu vcore was there.

 

[2informaticos]

You get even pulse on VCORE, so should be another problem on the MLB.
Tried SMC bypass now?
Test the board alone, only USB mouse connected.

 

[air_chair256]

When U7400 isn?t on the motherboard the voltages don?t pulse and the fan spins continuously but there is no vcore because u7400 isn?t there to generate it
i put u7400 back and tried smc bypass and no change still power cycling only the fan spins faster
i tried to connect a USB mouse and it lights up for a little then the light turns of but when i move the mouse it lights up again, but with the motherboard power cycling and not booting the mouse shouldn?t be working so...
and i?m testing the board alone, only the fan is connected

 

[2informaticos]

If you powered on the board without U7400, trash it; CPU is dead now.
NEVER let the Gate of high-side MOSFET floating on the air!!!

 

[JohnB8812]

Yeah this is now junk