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Indeed. I heat the board square cm per square cm, I finally found that heating U7200 allowed to start the board. Tiny short between pin 10 and 11...
Now ok, thanks!
Cold, the board does not want to start. Again, no pulses on SMC_DELAYED_PWRGD
I tied again together pins 5 & 6 with U1950 present, I have pulses on pins 7 and 3, but the board does not start, SMC bypass or not, just fan spinning 1 second, as before. Don't know where to go. It worked, I could...
Finally found a tiny corrosion spot around C4090 C4691 linked with PP5V_S4RS3, which gave also a pulse previously. Cleaned around and now the board starts alone, let's see for how long.
Thanks for this very detailed investigation! Always learning
I tied them without U1950, and for some reasons I had pulses on SMC_DELAYED_PWRGD
Reinstalled U1950, I could start the board (blinking folder) by triggering SMC_ONOFF_L, with power supply giving 700mA, a bit higher than normal. The board did not start alone when giving power.
When trying later...
Pulse on pin 7 ok, no pulse at pin 3.
I had pulses on SMC_DELAYED_PWRGD, but not at each trigger of SMC_ONOFF_L
Removed U1950, I got a couple of pulses on SMC_DELAYED_PWRGD, then no more. Do this pulse should appear at each SMC_ONOFF_L trigger?
R5191 ok
Fan spins first low speed a few seconds...
Q8150 removed, pulse of 3.4V on ALL_SYS_PWRGD, exactly same behaviour in SMC bypass mode, fan is spinning half a second, then quarter fan spin, and repeat
Without internal SSD, did you try to boot on a old OS X (e.g 10.13) in a USB key?
I had cases where internal SSD prevented to recognize other boot possibilities
You mean the same for PM_SLP_S3_L? There is also a brief pulse from 0 to 3.4V
Power rails:
from PM_SLP_S4_L :
P3V3S3_EN
P1V8S3_EN
DDREG_EN
all have a pulse at 3.4V
from PM_SLP_S3_L :
CPU_VCCST_PWRGD: pulse at 1V
P5VS0_EN
P3V3S0_EN
P1V05S0_EN
all have a pulse at 3.4V
In SMC bypass mode: PPBUS_G3H=8.2V, the fan is spinning half a second, then quarter fan spin, and it starts again half a second, then quarter fan spin... Sometimes the fan is just ticking.
I have pulses on L7520, L7630, L7430, L7310, L7320
No pulses on L3095
3.3V on L7560, 8.2V on L7130
The board looks ok, no fan, power supply gives 20-30mA with pulses at 120mA every 3-4 seconds as if it wanted to start but cannot
PP3V42_G3H=3.44V
PPBUS_G3H=8.6V
PP5V_S5=5V
PP3V3_S5=3.3V
PP3V3_SUS=3.3V
PP5V_S4=bursts every 3-4 seconds no readable
PP3V3_S4=bursts every 3-4 seconds at 3.3V...