820-00244 All power rails present, S0 state, not booting

[macdude101]

Got a MacBook 12" A1534 2017 (820-00244) here which at first glance draws power, trackpad becomes clickable, however caps lock key does not light and it doesn't output to an external display. Noticeably it gets very hot compared to a good board/laptop when left alone.

Nothing visible on the board, looks clean. All powers rails are present and ALL_SYS_PWRGD is good. SYS_DETECT_LED is also present. PPVCORE_S0_CPU is 0.795V which is about the same, if a tad higher than a known good board.

I turned to looking at the SPI. When measuring with a multimeter (don't have an oscilloscope at the moment for this) on a known good board I see SPI_CLK oscillate for around 10 seconds after power input and see similar on SPI_MOSI however I don't see that on this board, it's static at 0V. Conscious I might be missing something in the 2-3 seconds after power input before the multimeter probes touch the board though.

Checked for short on SPI_CLK using diode mode, measured 1.58V vs 1.62V on a known good board.

Unsure where to look next.

 

[2informaticos]

First of all, welcome to the forum!

You should check for USB activity first.
Already explained on the forum, few ways to confirm activity.
These boards are known by CPU internal problems.
Your description also points in that direction...

 

[macdude101]

Thank you!

No USB activity, tested with an optical USB mouse, no red light.

One interesting behaviour I did observe when I first received this laptop was that if booted with USB-C connected to another laptop (e.g. for target disk mode) the trackpad would not even become clickable when power was applied.

From reading other threads about 820-00244 I'm aware it may be a bad CPU and this might be the case here.

 

[2informaticos]

I don't recommend to accept these boards for service even.
You can just fix a power problem and client will come back few months later; claiming warranty for non working board, caused by dead CPU.
Try to explain him that you didn't even touch the CPU before...

 

[macdude101]

Yeah. This one actually came in from someone I know, wouldn’t normally take a 820-00244 unless it was an obvious issue like a screen replacement.

Before I throw in the towel on this. Is there a good way to verify whether this is a bad CPU or something else, say bad SPI/BIOS?

 

[2informaticos]

You should see SPI activity on the first seconds only.
After that CLK and MOSI lines usually stay at 0V.
You can heat CPU and test.
Videos about reballing it available on Internet, but not worth in my opinion...

 

[macdude101]

I see SPI activity for around about 3 seconds on this board and then the lines stay at 0V. On a known good board though I see those initial 3 seconds of activity, then activity for around about a further 5 seconds.

Worth flashing a known good BIOS potentially? Otherwise I don't think I'm going to go any further, not worth it if it's the CPU.

 

[2informaticos]

You can try BIOS, but I doubt is the problem here...