820-00923 - no SSD - missing clock signal

[2informaticos]

You can't get SSD clock with J9600 disconnected.
PCH expects some confirmation that SSD is present.

Compare all SSD signals with good board.

Not sure yet if SSD must have low, or high level on clock request line.
Some people reported high level in working state; opposite to airport situation.
SSD clock must be available for check on the other side, near U9100.

 

[realmacmods]

Ok, i found the test points. Kind of hidden under one of the NAND shields. Running a USB install presently, but when that finishes im going to check for clock there.

My thought on the clock request needing to be low is that it should normally be held high through r2080 (from 3v3_S0) until it can be taken low by a logic signal from the CPU through r2084.

 

[realmacmods]

Ok, can confirm there is no clock signal on either of those test points near u9100. PCIE_CLK100M_SSD_LBp/n

Also my boot after the OS install on an external USB drive failed with the message of not being able to install a needed firmware update. This happened both on Sierra (OEM OS) and Ventura (Latest OS) from Internet recovery.

 

[2informaticos]

The touchbar requires internal SSD to install its firmware.
Did you try to boot in safe mode, from external macOS?

Compare the SSD control signals (reset, enable, clock request, etc) with good board.

 

[realmacmods]

Tested every pin on u9300 just to be sure. Everything checks out as normal. i think I can almost certainly rule out a power issue with the SSD at this point

I dont have a known good board to test with at this time. What else is critical to the SSD that i can point my efforts to? U8600 looks important but is going to be difficult to accurately test given the pin count.

 

[2informaticos]

Do you get 24MHz at Y8600?

 

[realmacmods]

i get elevated steady voltages, but no discernible clock signal. Solid 1.8v on XTALi and solid 0.9V on XTALO
I also noticed that SSD_BOOT_L is at a constant 1.8V. _L suggests to me it should be logic low, but you never know with these things.

 

[realmacmods]

I just swapped y8600 with a donor board. No change. r8600, and r8602 measure correctly. I assume that this should be a simple crystal oscillator at 24mhz?

Booting Linux with y8600 removed from the board yields no change positive or negative

 

[2informaticos]

An o-scope should catch clear 24MHz oscillation there.
If not available, compare DC levels with working board.

 

[realmacmods]

this clock situation may not be relevant. I just looked it up and the scope im using maxes out below 1MHZ, so there is a very good chance my measurements are irrelevant.

 

[2informaticos]

Get an working A1706/7 board for comparison...

 

[realmacmods]

giving up. now randomly has a short through u8600 that was not there before. probably a bad u8600 all along

 

[2informaticos]

You should try changing U8600.