Macbook A1708 - 820-00840 20v 50ma

[obelix24]

Hi All I've one MacBook A1708 that is taking 20v 0.05a

I've checked and there is short to ground on PPBUS_G3H but I'm not able to locate it.

I've injected voltage on F7000 (1V 3A) but it was taking only 0,2a.

I've checked also C6465 but it's ok (I've take it from board and test with multimeter) - also when it was removed short was still there.

Can you please help me what is causing the short ?

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

Remove all power. Meter in resistance mode.

What is the exact resistance to ground at F7000?

Flux and remove F7000. Power up again. Is the ISL side now able to deliver a correct voltage for ppbus_g3h?

Remove all power. Measure the resistance from the removed F7000 downstream pcb pad to the Vcore rail.

What is the resistance? This is checking if the high side CPU rail mosfet(s) is leaking or not.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

1. resistance on F7000 (still on board) - both sides 3,7ohm
2. fuse removed, power via USB-C - 13,08V stable on ISL side
3. first pad (ground) - 3,7ohm, ISL pad OL

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

Check the resistance from the removed F7000 fuse pcb pads to PPVCCCPU_S0G.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

it's quite hard as test point is on the opposite side of the board but on
1st pad (ground) resistance to test point - 10ohms
2nd pad (ISL) - resistance - 5Mohms (mega ohms) and it's falling down.

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

The trick here is to view the boardview for this logic board -> locate the netname for the power rail to inspect.

Then the viewer will highlight all test points for the same rail and hoping that you can access a location on the same side as the F7000 fuse.

Then place one meter probe on the downstream (consumer) side of the removed F7000 fuse. Other meter probe to the power rail that powers the CPU. Again, checking to see if the highside mosfet is leaky.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

Yes this is how i tested and result are also there but sadly no test points on same side as the fuse

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

Ok. Can you confirm the resistance between the 2 points? This is the downstream side and the CPU power rail.

What is the resistance?

No power to the board while checking resistance.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

Sorry but i don't understand now what resistance should i check/confirm ?
Resistance between f7000 and PPVCCCPU_S0G ?

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

Yes. The F7000 fuse has 2 pads. One side is with the ppbus_g3h voltage. This is the ISL side or the producer side since the ISL creates this power rail.

The other side of the fuse is the consumer or downstream side.

Check the resistance from the consumer side to the CPU power rail. This is to check if the CPU rail was possibly hit by a high voltage spike due to a defective high side mosfet. This means the CPU is dead.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

I can confirm that results are :
1st pad (ground) resistance to test point PPVCCCPU_S0G - 10ohms
2nd pad (ISL) - resistance to test point PPVCCCPU_S0G - 5Mohms (mega ohms) and it's falling down.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

I hope it's not dead CPU from this measurements

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

Inject 1 volt (only) @ downstream side of the removed fuse from PPBUS_G3H rail.

While doing this injection from your power supply, check the voltage to ground of PPVCCCPU_S0G. If you see a voltage @ PPVCCCPU_S0G, then the highside mosfet is leaking.

There is hope that the current draw is low so the CPU may be ok.

Had a case yesterday that is still in motion for the repair. A1466 motherboard that died suddenly with no liquid spill. The current draw is a fixed 56mA from the host external power supply.

The fuse @ F7140 was damaged -> replaced it -> saw the current spike to 360mA (not higher) and smelled a burning smell which was the fresh fuse on ppbus_g3h rail.

The resistance to ground of the removed fuse = 0R3. Feared the worst but injected 1 volt and found the current draw to spike to 7A. Kept repeating the pulsing of the injection and one of the tantalums split open. Removed it and the resistance is now higher. Have some fresh fuses in transit today to continue this review.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

so voltage on test point is 0V while injecting 1V to PPBUS_G3H (fuse F7000 pad)

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

Keep the voltage injection on at 1 volt on the consumer/downstream side of the removed fuse.

What is the current draw showing from your power supply used for the injection?

Our A1466 is fixed. The same process located a tantalum that was shorted, split open and was removed. Replaced the fuse for the 3rd time. Had fan spin and normal boot. Client was very happy she did not need to buy a new computer.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

i've left power supply on for some time and current draw went down from 0,2a to approx 0,09a

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

Ok. Check the resistance to ground again for this rail. It should now be at a higher resistance.

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

Today I've checked board with thermal camera and I noticed that when I inject voltage (1V) to PPBUS_G3H (F7000 pad) one component (Q8060) gets hot (not extremely as it takes only 0,2a.
I've replaced it and now when I connect charger (F7000 is back on board) is taking 5V then it jumps to 19 and 20V and Amp goes up from 0,05a to 0,3a.

I will put board back to housing if there is any display ...

[obelix24]

Re: Macbook A1708 - 820-00840 20v 50ma

Ok it stays on 20V 350mA ...
I've checked PP5V_S5 but there is 5V so this is ok.

Mon2 do you have any suggestion ?

[mon2]

Re: Macbook A1708 - 820-00840 20v 50ma

Review this same case here:

https://repair.wiki/w/A1708_2016,_20...ar_MacBook_Pro

One outcome is that the CPU is damaged. Hope it is not. Do review and post your progress.

Check the resistance of the CPU power rail to ground. Does the CPU power rail enable?