Macbook Pro a2141 820-01700 - short on PPBUS

[shlomim412]

Hello

working on a dead a2141 logicboard - 820-01700

no power, on usb c ampmeter it's on 5v drawing 0.01a

visual inspection under the microscope - board look good, no liquid damage on any kind of damage.

ppbus_g3h is 0.3v, and is shorted to ground showing around 50ohms (continuity beep) and climbing..

i removed F7000 and F7001 and now getting 12v on PPBAT_G3H..

also verified the short is on the system side (pin2 of F7000\1)..

i tried to inject voltage, 1v to ppbus_g3h but it's only drawing 0.02-0.03a
and i can't feel anything getting warm, also tried some isopropyl on some spots but can't seem to locate where the short is...

any ideas?
i'm worried to get the voltage up not to damage ssd\cpu in case the short is around there..

thanks..

[mon2]

Re: Macbook Pro a2141 820-01700 - short on PPBUS

Meter in resistance mode. One meter probe on the downstream side with the low resistance of ppbus_g3h.

Other meter probe to the Vcore pin that powers the CPU.

Post the measurement. Checking to see if you have a high side CPU Vcore rail mosfet that may be leaky.

[shlomim412]

Re: Macbook Pro a2141 820-01700 - short on PPBUS

hi
i measured between PPBUS_G3H (shorted pin of the circuit) and PPVCC_S0_CPU and is around 133ohm.

[mon2]

Re: Macbook Pro a2141 820-01700 - short on PPBUS

Measure the resistance to ground of PPVCC_S0_CPU. Be sure that there is NO power to the logic board when measuring resistance.

reference reading (5:31PM by @Piernov):

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

[shlomim412]

Re: Macbook Pro a2141 820-01700 - short on PPBUS

resistance to ground is 3.3ohm on PPVCC_S0_CPU

[shlomim412]

Re: Macbook Pro a2141 820-01700 - short on PPBUS

resistance to ground is 3.3ohm on PPVCC_S0_CPU

is that considered normal? it should be low resistance, right?

[mon2]

Re: Macbook Pro a2141 820-01700 - short on PPBUS

Inject again the 1v on ppbus_g3h and measure if you see the voltage on the above CPU power rail.

[shlomim412]

Re: Macbook Pro a2141 820-01700 - short on PPBUS

hi
i injected 1v to the ppbus and is not showing on the cpu_s0 rail...

[reformatt]

Re: Macbook Pro a2141 820-01700 - short on PPBUS

First thing I check on these newer MAC's are the caps at the edges. Fan intakes were redesigned compared to the older non-T2 machines and result in corroded caps in those areas. Then check the SSD's 2.5V rails to ground on each one. If you get low ohms, it's usually game over.

Also check PP3V3_G3H_RTC_X output (U6960) to ground, but I think you will be ok here as your current draw via USB-C is so low.

[shlomim412]

hi
bumping up an old thread, sorry about that

no short on 2.5v ssd rail

i injected voltage to ppbus with the fuses off the board
it went up to 3v and around 2.5 amps draw..

the only thing i noticed is the ram on the back is getting hot
took out the plastic cover but seem like the whole area is getting warm but couldnt figure out what causing it...

any ideas where to check? what can cause ppbus to short ?

sadly i do not have a thermal camera...

[mon2]

Without the fuse and no power, what is the resistance to ground on the downstream (consumer) side of ppbus_g3h?

you can use ipa (alcohol) to hunt down which part is heating up. Could be a nearby cap in the region?

have the same pig of a board in for service - 2nd one this month.

you can use the meter in resistance mode to locate the area of fault by checking resistance between this downstream point of the removed fuse and the high side mosfet where the rail travels. That is, this high voltage is used by assorted points on the board as a buck regulator (creates a lower power rail) using a high and low side mosfet pair. Check the resistance of each such mosfet and also the local inductor and the ppbys_g3h point. Hope that the fault is only a shorted cap.

[shlomim412]

a thermal camera can be useful in a case like this?

is it risky to inject more voltage and maybe than the fault component will be more obvious?

resistance to ground on the system side without the fuse and power is 60ohm and climbing...

[mon2]

Do not inject higher voltages onto the board. The logiwiki links have changed so here is a fresh one that is working for this topic review:

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

Remove all power. Meter in RESISTANCE mode. Place one meter probe onto the fuse pad where you are noting the 60 ohms to ground. Other meter probe onto any inductor on the board. The idea is that each such inductor is likely linked to a buck regulator that creates a lower voltage rail from ppbus_g3h. So you are checking if there is a low resistance path from the main ppbus_g3h to this point under test. List any such inductor for a further review.

Also forgot to ask earlier - without the fuse installed and power applied, do you now see a valid ppbus_g3h voltage on the producer (ISL) side of the removed fuse?

[shlomim412]

hi
without the fuse it seems like ppbus on the producer side is fine - around 12.3v steady.

the inductors on these board are the ones that above the cpu\gpu? or others around the fuses?

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance to ground of CPU VCore rail. Next, measure the resistance from the downstream removed fuse pcb pad to the same cpu vcore point. If this resistance is 0 ohms then the high side mosfet is damaged and the cpu is probably dead because the high voltage has reached this low voltage rail. Post all measurements.

Be sure to review this webpage:

https://repair.wiki/w/A2141_2019_16%22_MacBook_Pro

[shlomim412]

hi
i'ts 3.6ohm between PPVCC_S0_CPU and ground

and around 37ohm and climbing to 150\200\300+ohm between PPVCC_S0_CPU and ppbus downstream pad. (with fuse removed ofcourse)...

is it correct? or too low readings?

[guruji]

this model has a history of ssd nand power getting short tps62180 U9580 and it also takes away the nand chips you have top change all 4 if they are 512.you could check if you take off the nand power chip u9580. will restore your ppbus but the machine will be in COMA brain dead.

[mon2]

I think your nand voltage was posted to be ok? Can you confirm this?

also, without power, measure the resistance to ground of u9580 output that powers the nand rail.

with isl side power rail at 12v3, T2 is not booted. This should be 12v6.

To me, the CPU rail resistance looks ok.

do you have another machine that can be used to DFU this machine?

[shlomim412]

with the fuse removed isl side should be more than 12.3v? i will check that again.. (t2 in on isl side, and not system side?)

i think ssd is fine since i can't find short in this area (on 2.5v rail for example)
i will measure u9580 and post...

i have another machine to try dfu... you suggest to put the fuses back and try DFU?

thank you!

[mon2]

Following the case studies on repair wiki. Our ppbus_g3h was at 12v6. Yours is not. Try dfu without and with the fuse on ppbus_g3h. This was our first use of the dfu and target mode tools earlier this week. Be sure your host machine is current on the operating system - we had Sonoma loaded. The client purchased the new a2141 we brought in so on the hunt for another dfu capable box. Be sure the interconnect cable is of quality and suggest 40g rated. Use the 2nd usb port on the left side of this box.