Macbook Pro A1990 820-01814-01 no power

[ryogadan78]

I have a problem with a MacBook with 820-01814-01 mainboard, the Macbook gives no signs of life, I have tried different power supplies.
I noticed a short (6ohm to ground) on the capacitors near the CPU, from board view the short is on the PPVCCGT_S0_CPU line. The very kind and super user mon2 has already told me that we can't consider short circuit 6ohm on CPU rail.
Another short (20ohm to ground) on other caps near CPU on the PPVDDCI_S0_GPU.

Is this normal?

Is there anything I can test?

There are no signs of water contact or other visible damage on the mainboard

Really thanks

[ryogadan78]

Hi Guys.
I found this topic and before I open a new one I would like to ask for help here.
I have a problem with a MacBook with the same mainboard, the Macbook gives no signs of life, I have tried different power supplies. I noticed a short (6ohm to ground) on the capacitors near the CPU, from board view the short is on the PPVCCGT_S0_CPU line.
Another short (20ohm to ground) on other caps near CPU on the PPVDDCI_S0_GPU.
Is this normal?
Is there anything I can test?
There are no signs of water contact or other visible damage on the mainboard

Thanks

[mon2]

6 ohms to ground for the cpu power rail is not considered to be a short. Start a new thread for a review.

[mon2]

Meter in DC volts mode (20v or higher scale is ok). Measure the voltage to ground of PPBUS_G3H @ fuse F7000 or F7001. Do measure both sides of these fuses with the power adapter connected (for now, disconnect the battery).

If there is no voltage present here, remove all power (no adapter / no battery) -> meter in resistance mode. Measure the resistance to ground on each side of these same fuses.

Post each measurement.

[ryogadan78]

Hi mon2, thanks for your valuable help and sorry for the delay, I only have access to the lab in the morning these days.
I measured the voltage both sides of the two fuses, always measuring 12.6V

[mon2]

This is a good voltage. T2 has booted and the SMC has boosted this rail to 12v6.

does the caps key led toggle?

is the power adapter voltage at 20v ?

Use of a usb-c meter will be very helpful. You can probably get one from Amazon. To view the adapter voltage and current draw.

Suggestions are to check the voltage to ground at each inductor on the board. Each inductor is linked to a local power rail. Note any inductor with 0v or incorrect voltage. The schematics will list the proper voltage for each inductor. If not practical, remove all power and check the resistance to ground of each inductor.

Check to see if the SSD power lines (0v9, 1v8, 2v5) have voltage.

If they have voltage try to put into DFU and attempt revive using another machine.

What was the history? Just stopped working?

[ryogadan78]

Hi, thank you again.

- the caps key led is off

- the power adapter is the original one, 20v, that works on another macbook

- I had a usbc tester, but it no longer works. I bought a new tester two days ago, it should arrive within a few days.

- I am having difficulty reading the schematics (but I can try), here are the measurements of the resistence to ground of each inductor
L7410 6.4ohm
L7420 6.4ohm
L7211 3.2ohm
L7221 2.9ohm
L7231 2.9ohm
LA340 2.7ohm
LA640 2.7ohm
LA650 2.7ohm
LA350 22.1ohm
LA350 217ohm
L8102 48ohm
L9080 1.5ohm
L9081 1.5ohm
I think these are the principal inductors, if further measurements are needed I'll do them right away

I am not sure where to take the measurements you requested for SSD lines. I tried:
P0V9_LX0_SSD0 (on L9021 inductor): 0.9V
P1V8_LX0_SSD0 (on L9030 inductor): 1.8V
PP2V5_NAND_SSD0 (on L9080 inductor): 0.2V
I notice that in this area the mainboard gets very hot


The notebook suddenly turned off; I'm pretty sure it still had a charged battery. Then it did not turn on again, I tried other power supplies but to have no success.

[ryogadan78]

Notably, doing the test with isopropyl alcohol, capacitor C9089 seems to be the hottest one

[mon2]

PP2V5_NAND_SSD0 (on L9080 inductor): 0.2V

this could be the deal breaker. The nand flash may be defective or someone on this power rail is shorted.

you noted the hot capacitor. Flux it and remove the hot capacitor. Then measure the resistance to ground again for this power rail. Then power up without this hot capacitor. Low air pressure but enough heat to melt the solder.

[ryogadan78]

Removed C9089... everything works wonderfully!
I also found a capacitor from a donor board that I put in place of the shorted one. But out of curiosity I could have also not put it in?
Thank you very much for the invaluable help. You are the best

[mon2]

The part could have been left off without a problem. Well done!! Good team effort.