MacBook Pro M1 A2338 820-02020 - No WiFI/Bluetooth or internal display

[mcbadcbv]

Hello,

I have a MacBook Pro M1 A2338 820-02020. It boots to OS but WiFi/Bluetooth are non-functional (exclamation point through WiFi symbol in menu bar) and the display is not working.

Starting at the WiFi chip... PP3V3_S2_WLBT_ISNS is fluctuating at around 2.4V. No shorts detected around UL000.
PPBUS_AON is 12V steady, but PPBUS_AON_3V3_S2_VIN_ISNS (measured at CC721) is 2.76V.
LC710 is getting 2.4V at P3V3_SW, which explains PP3V3_S2 fluctuating around 2.4V.
No detected shorts around UC710.

This makes me believe that RD560 has failed and is not supplying CC721/UC710 with 3.3V. This is a common issue according to other threads I've read.

Does this sound plausible? My next question is, what type of component is RD560, and is it possible to order one? I do not have any donor boards at the moment.

First post and I'm a beginner repairing a personal machine. Appreciate any insight!

[mon2]

RD560 is a current sense resistor. Rare for this part to fail. Remove all power. Measure the resistance across this part. Touch your meter probes together. Compare the 2 values from these measurements. Each should be identical since most meters cannot measure such a low resistance like that at RD560.

If you see a much higher value here then yes, RD560 is a suspect. Replacements should be available from Digikey / Mouser.

What is the exact resistance to ground of LC710 ? The fault may be in the feedback resistors on the same switching regulator. The resistors are used to define the output voltage.

[mcbadcbv]

RD560 is a current sense resistor. Rare for this part to fail.

Thank you for explaining that. Here were the threads I was referencing that pointed me to RD560:

• https://boards.rossmanngroup.com/thr...03/post-100217

RD560 must have same voltage on all 4 pins.
However, important is to get 12.5V at UC710.
That means RD560 is good.

I do not believe UC710 is getting 12V on my board because PPBUS_AON_3V3S2_VIN_ISNS is only getting 2.76V (measured at CC721).

• https://boards.rossmanngroup.com/thr...964/post-99850

What is the exact resistance to ground of LC710 ?

Not sure if I'm able to get a good reading - seeing 65K Ohms. It climbs (charging?) but slows to 65.

Thanks for your help.

[mcbadcbv]

Sorry, just realized a mistake in my original post - I meant to say 12V not 3.3V. It should read:

"This makes me believe that RD560 has failed and is not supplying CC721/UC710 with 12V. This is a common issue according to other threads I've read."

CC721/UC710 is only receiving 2.76V on my board at the moment.

[mon2]

Remove all power. Measure the resistance to ground of CC721/UC710.

What is the exact measurement in ohms?

[mcbadcbv]

Resistance is to ground is very high at ~10 Mohms.

[reformatt]

Interesting! At face value, it does look like RD560 is open or high resistance (or corroded underneath). It's a 50 milliohm 1/3W current sense resistor, can't say I've ever seen a CSR actually fail, but then that's just me.

There are plenty of these resistors on older boards (search for 107S00017 in FlexBV shows many models have it). So if you have some old T1 or T2 boards you should be able to locate a donor. Failing that, closest I found was one from LittleFuse (P/N: L4CC0306QLR050FNR). Available from Mouser or Digikey.