iMac M1 A2439 (820-02188) – 3 LEDs On but No Boot

[SmartDoc]

Hey everyone,
I received a completely dead iMac M1 (A2439, 820-02188, 2-port version) — no signs of life at all when trying to power it on.

I disassembled it and checked the debug LEDs — all off.
Flipped the board and found a shorted capacitor near the main power manager.
After some further analysis, I also found an inductor with very high impedance, which according to the schematic appears to be part of the 5V boost circuit.

Replaced the shorted capacitor
Replaced the inductor with identical one and a brand new mpmu

Now the Mac partially powers on:

• • I get the 3 debug LEDs on, but nothing else happens
  • It doesn’t enter DFU mode, no reaction to reset commands

Voltage rails checked – all OK:

• • 3V8_AON: 3.770V
  • PMU_RESET_L 1.8v
  • PP3V8_AON_VDDMAIN
  • PP5V0_S2
  • PP3V3_S
  • PMU_ACTIVE_READY
  • PMU_SYS_ALIVE

i also checked from signals to and from SOCROM and SPI , SPMI and SGPIO bus but as i can see nothing is communicating

Current issues:

• 
  
• • No response to SOC_FORCE_DFU
  • SOC_DFU_STATUS is always low
  • If I hold the power button for 10 seconds, the 3 LEDs turn off, then come back on

Seems that Soc is in hold and is not booting, can i check somewhere?

Has anyone seen similar behavior on this board before? Any suggestions on where to go from here?
Thanks in advance for any input!

 

[2informaticos]

First of all, welcome to the forum!

Do you get now 5V at C8300?
Did you test external video and USB activity?
Did you get the MPMU from same model donor board?

Tried using external switch method (over SV000)?

DFU Mode Restore (Macs) - LogiWiki

We have Apple MacBook and iPhone Diode readings and general fault finding information compiled by the leaders in this area

logi.wiki

Solder RV001, if is not present; or use its pad 2 for the switch.

 

[SmartDoc]

First of all, welcome to the forum!

Do you get now 5V at C8300?
Did you test external video and USB activity?
Did you get the MPMU from same model donor board?

Tried using external switch method (over SV000)?

DFU Mode Restore (Macs) - LogiWiki

We have Apple MacBook and iPhone Diode readings and general fault finding information compiled by the leaders in this area

logi.wiki

Solder RV001, if is not present; or use its pad 2 for the switch.

Hello, is my great pleasure to be here

yes C8300 have 5v, no activity on usb c ports, no dfu status.

MPMU is brand new

I already soldered RV001 but if i bridge SV000 Nothing happen. DFU_STATUS signal still 0v and in usb c have no dfu communication. Also i don't have any activity on SocRom and Spi

 

[2informaticos]

Follow the instructions on that link.
You may need to play with that switch and power button also.

BTW, write directly into bottom reply box, instead of clicking Reply button.
I don't see any reason to quote an entire post, visible few centimeters above.

 

[SmartDoc]

ok thanks for the precision but sorry I'm new here

I tried in every way with Force_Dfu but in any case it doesn't go into dfu and DFU_STATUS is always 0v.. now I'll try to do another test by assembling the mac in the body and connecting the display (could it be the lack of the latter that doesn't make it go into dfu?).

is there any other line that I can check regarding mpmu and spmu or the tbt usbc controllers?

thanks for the help

 

[2informaticos]

Not sure if new MPMU works there.
You should try one from same model donor board.

 

[SmartDoc]

the new PM already cost me €60, damn it... I can't find donor motherboards anywhere, do you have any?