Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Leave at 5A. We want the shorted part to heat up.

For safety, keep the voltage at 1v or even 0v8.

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

I didn't noticed anything heat up. There is still short.

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

When the power supply at 1v is applied, what is the current draw?

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

2 ampers

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Confirm if the power supply is being current limited. If yes, increase this value to 5A and test again.

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

It's not. I set it to 5A. Still get only 2A.

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Increase the voltage to 2 volts and test again. Monitor who is heating up.

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

I found it. It's C6555 and C6556. They are very hot.

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Excellent!! Flux and remove both of these parts.

Be sure the pads are not shorting and then check the resistance to ground again if F7000, pin #2.

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

I already removed C6555 and there is no short anymore. I can measure F7000, but I will do it on Monday. I must go out. I will reply on Monday.

Thanks again. You are very kind.

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Excellent! Place back the removed fuse and test it all again.

Thanks to @Piernov for the clarity on how to test the short condition - initially to me, thought your CPU was shorted.

This is a good read as well:

https://logi.wiki/index.php/PPBus_G3H

Review the article on PPBus Shorts (@Piernov).

Will cross my fingers waiting for some good news on Monday.

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Just to be sure, you mean place the fuse back, connect it to power supply trough USB-C and see If I get 20V?

Sorry for dumb questions, but I'm really a newbie. And I don't want to kill the board completely.

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Yes. Remove all power to the board. Start with posting the resistance to ground of the F7000, pin #2 so we can be sure the short is gone. Then solder back the removed fuse and confirm the voltage of PPBUS_G3H.

Ideally, this was the only root cause and the unit should be repaired.

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

It's about 5MΩ.

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Good resistance. Solder back the fuse and test again.

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Now I get 20V on all ports. You are the best! Thank you very much!!!

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

Sadly, when I put PCB back it still won't turn on. Maybe there is another problem.

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

What is the voltage and current draw? Is the current draw stable or cycling?

What is the voltage to ground reading of PPBUS_G3H @ F7000 ?

[martyjelen]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

20V / 0.436A - stable

Voltage at F7000 PPBUS_G3H is 12.5V. I noticed that U7800 is hot.

[mon2]

Re: Macbook A1989 - 820-00850-A Won't turn on - stuck at 5V/5mA

What is the voltage to ground of ALL_SYS_PWRGD_R ?

Perhaps try DFU.