A1708 820-00875 won't power on; 20V 500mA initially, then 0A.

[ipmungam]

Our 2016 13" mbp has had some issues since liquid got into one of the USB-C ports a few years ago, but it was working well with the latest (aftermarket) battery for several weeks -- until now.

With the board out and no battery, it negotiates 20V properly and starts to take 300-600mA (let's call this phase 1). With the screen attached it will even show the red low battery icon. Then after 5-10s the current drops to near zero and nothing more happens (phase 2). Power button has no effect.

I have checked all the coils I can see while unpowered and none seem shorted to ground. PPBUS_G3H is 13V during both phase 1 and 2; the other power rails seem to power on during phase 1 (I only have a few seconds to check, so can't be sure, but the display briefly works so must be something right). However most everything other than PPBUS_G3H goes to exactly 0V in phase 2. It's as though they're being shut down.

Any thoughts most welcome.

[mon2]

Flux and remove F7000. Power up again. What is the voltage to ground on the removed fuse pcb pad # 1 ? Is it stable or still power cycling?

[ipmungam]

Thanks very much for the speedy reply -- I will try this and report back.

[ipmungam]

Hello again. Took some work but I got F7000 off -- now the board negotiates 20V but never takes more than 20mA, which I suppose makes sense.
The voltage at the F7000 pin is a steady 13V. This is consistent with when the fuse was in -- it wasn't power cycling so much as it seemed to start the pre-boot process (phase 1), but then got interrupted at some step and shut down the rest of the power rails.

[ipmungam]

I've tested resistance to ground for all the power rails I can see listed in the schematic -- no shorts as far as I can tell.
This suggests I'm missing an enable signal somewhere -- any suggestions on where to start looking would be welcome.

[mon2]

Do you see the same low battery graphic with and without the battery attached? Can you test with another known good battery? Amazon?

[ipmungam]

Thanks. With F7000 removed I have reinstalled the board with the "new" battery (recently bought on Amazon and worked for 1-2 weeks) and "old" battery (bought aftermarket a few years ago, swollen cell). [I don't have the "original" battery anymore.]

0. No battery: 20V, draws 0-40mA, no longer seeing the low battery screen (to see an image does F7000 need to be in place?).
1. New battery: 5V, power cycles every time it tries to reach 20V.
2. Old battery: 20V, draws 0-40mA, no screen.

[mon2]

Yes. Add fuse. Test again and confirm the graphics.

[ipmungam]

Just got back to this, F7000 is now back in. Yes, with the old battery attached the behaviour is exactly the same as first reported, but now with an extra ~300mA draw -- the low battery graphic comes on both with and without the battery, but shortly after that the current draw drops to zero (or to 300mA if the battery is attached).

Seems as though the new battery failed and in doing so took some enable signal(s) somewhere in the power up sequence with it.

[mon2]

Attach the battery. Measure the voltage to ground of each pin on the battery connector. Post each measurement.