820-3115 Fan Spins, no PPVCORE_S0_AXG_REG

[awbower]

All S0 signals are present except for PPVCORE_S0_AXG_REG. PPVCORE_S0_CPU_REG is present, but low (~1.1V).

Even though PPVCORE_S0_CPU_REG is present, U7400 is not giving me CPUIMVP_PGOOD. It is also not outputting CPUIMVP_AXG_PGOOD (obviously, since PPVCORE_S0_AXG_REG is missing). I need both of these signals to get PM_PCH_PWRGD.

In order to get PPVCORE_S0_AXG_REG, U7400 must output 4 signals to Q7550 (pg. 69 of schematic). None of these signals are present. I replaced U7400, but it did not change anything.

To try to address low voltage on PPVCORE_S0_CPU_REG, I replaced Q7510 and Q7520. This did not change anything.

I checked the current sensing associated with R7510 and R7520. No problems found with resistors or traces.

 

[awbower]

"I need both of these signals to get PM_PCH_PWRGD."

It turns out you are right. I will explain how I know in a moment. However, please take a look at pg. 3 on the schematic. Step 27. There is an AND gate with CPUIMVP_PGOOD on one side and CPUIMVP_AXG_PGOOD plus some other PGOOD signals on the other. If all those signals are present, PM_PCH_PWRGD comes out the other side. Am I reading that correctly?

Strangely, the schematic seems to contradict itself. At the bottom of pg. 24 it looks like you can get PM_PCH_SYS_PWROK with just CPUIMVP_PGOOD and ALL_SYS_PWRGD. Also worth noting: PM_PCH_PWRGD mentioned on pg. 3 step 27 does not appear anywhere else in the schematic. It seems like they changed the name on pg. 24 to PM_PCH_SYS_PWROK.

On this board, ISL 6259 was blown. After I replaced this chip, the board powers on most of the time. However, occasionally i do lose fan spin and green light on charger. I replaced SMC to try to fix that but it still sometimes happens.

I was spending my time trying to get CPUIMVP_AXG_PGOOD and didn't even test for boot. It turns out that when the fan does spin, it actually does boot. Any suggestions on why it is unstable and sometimes not power on?

 

[2informaticos]

Need to know what happens with PPBUS_G3H and 3V42_G3H when board doesn't turn on, as you also lose Magsafe light at that moment.
Also monitor SMC_RESET_L.

Battery is charging?
Doesn't turn on even if battery is connected?

 

[2informaticos]

Check voltage and diode mode on SCL/SDA lines of that I2C bus.
Be sure R5260/61 are good.

Run HWMonitor and look for strange values related with U5511.

 

[2informaticos]

SMC reads CPU core temp directly from CPU.
If U5511 does not interfere, then should be a problem with the CPU.