Macbook a2141 - logicboard 820-01700 no wifi\bt

[shlomim412]

Hello
working on a2141 macbook, board number 820-01700 which has no wifi\bt and also no connection with LAN cable.

initial visual inspection the board looks good no visible corrosion or damage.

i found that PP3V3_G3S_X is shorted to ground (around 1.5ohm short)
and also PP3V3_GS3_WLAN i shorted to ground (same ohm reading, around 1.5ohm).

the board is working but no WIFI\BT as i mentioned.

with the usb c cable connected for measurement i noticed U8215 i getting EXTREMELY HOT
so i pulled it out figuring it might be causing the short, but it didn't..

still same short, now with usb cable connected this specific area is not getting warm anymore..

any ideas how to proceed? inject voltage?

thanks..

[mon2]

If U8215 was getting very hot, check surrounding parts in this region. Check each and every part's resistance to ground that can cause this region to heat up. Someone is shorted in this area.

still same short, now with usb cable connected this specific area is not getting warm anymore..

???

If someone is shorted, it will heat up.

[shlomim412]

hi
"still same short, now with usb cable connected this specific area is not getting warm anymore.."

by that i mean - after i pulled out of the board U8215 - this area is no longer getting warm..

also all pins under U8215 seems to be ok and not shorted other than PP3V3_G3S_X ofcourse..

pulled out U8215 hoping it might be the cause of the short... but with it out of circuit PP3V3_G3S_X is still shorted...

[mon2]

What is the voltage to ground of:

PPBUS_G3H
PP1V8_G3S
PP5V_G3S

20v on power adapter usb-c port? Current draw without battery?

PP3V3_G3S_X resistance to ground?

Do you have a dc power supply for injection?

[shlomim412]

hi
yes i do have power supply for injection...

you mean voltage to ground on
PPBUS_G3H
PP1V8_G3S
PP5V_G3S

with usb c power connected?

i think i would have to put back U8215 for it to go to 20v again...

resistance to ground on PP3V3_G3S_X is around 1.9ohm.

[mon2]

Inject 1v at 3-5A onto this rail and check who heats up. Do not go higher than 1v.

[shlomim412]

i injected 1v to PP3V3_G3S_X and it only draws 0.02amp

nothing seem to get warm... got it up to 1.5v around 0.04amp draw.. nothing seem to get hot...

could be bad U3730 at this point?

[mon2]

Some misunderstanding here. If you truly have a 1R5 ohms resistance to ground on PP3V3_G3S_X rail then someone will be heating up and the current draw will be much higher. Since you do not have this observation of the current draw, the resistance measurement may be in error.

Remove all power -> meter in resistance mode -> measure the resistance to ground again of this power rail. Post a pic of the front face of your meter for a review.

This power rail is being switched through a load switch (acts like a solid state relay) @ U8215.

[shlomim412]

you are absolutely right, so it's either i was readng the meter wrong or something changed after voltage injection.

now i was reading 52ohm on PP3V3_G3S_X and PP3V3_GS3_WLAN

so i ended up soldering "new" U8215 from donor board (which was getting extremely hot at the beginning when nothing worked)

now getting 3.3v on both rails

now, it looks like a tough nut to crack because now WIFI WORKS before recovery screen (on black screen with earth logo),
but not in the recovery itself... i ended up installing with LAN cable which also didn't work before.

now with os installed - LAN works, BT works but wifi keep saying - connection failed.

only on OS it doesnt work, when i connect to wifi for diagnostic screen (black screen on startup) it works.

also diagnostic pass with no issues..

progress, but still hard to figure out - also 52 ohm still seems low...

sorry for the confusion, any idea on how to proceed?

[mon2]

I assume you have performed a PRAM reset and SMC reset. If not do that first.

Yes the resistance is still considered to be low. Will trace the region in a bit. In the meantime, test if this new load switch is enabled or disabled when you lose the wifi.

[shlomim412]

hi
RRAM and SMC reset didn't work. already tried..

the load switch put out 3.3v constant on both these lines, so looks to be enabled..

the wifi only works before the OS is loading... on the black screen with earth logo
for example, before recovery, or before diagnostic screen..

in the OS it detects the networks, but won't connect keep saying - connection failed

[shlomim412]

can you please say what connects between these two lines?
PP3V3_G3S_X and PP3V3_GS3_WLAN ?

when i inject to PP3V3_G3S_X i see the voltage also on the other line.

r5530 seem to be missing... also missing on other boards from the same model as well.

thank you mon!

[shlomim412]

update - tried everything possible related to software - update, safe boot etc... and still seem like wifi is only working out of OS and not in OS regardless of the version..

could the problem be the low resistance on both these rails - PP3V3_G3S_X and PP3V3_GS3_WLAN ?

if yes, would love for an idea on how to diagnose it and find the cause..

thanks..

[mon2]

r5530 seem to be missing... also missing on other boards from the same model as well.

hmm...have these boards been worked on before? By another shop? I could be wrong here but believe this current sense resistor and related parts should be present on the board.

Do you see U5530 onboard? If yes, then this current sense resistor should also be present otherwise, the op-amp will report the wrong condition of the current sense.

[shlomim412]

r5530 and u5530 is missing
the boards never been touched, all original and look like it's missing by design.

here are some attached photos of it..

also missing those components on a good working board

the low resistance on these rails could be the cause of the issue - PP3V3_G3S_X and PP3V3_GS3_WLAN ?
what is connecting between the two?

if yes, how would you recommend to try and resolve it?

thank you!