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820-2849-A no chime PPBUS_G3H intermittent 8.33v/1.9v

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dukefawks

Administrator
First check pin 25 on U7600 if enable is there. I bet it is and this problem is caused by the feedback from the CPU on the CPU_VTTSENSE lines. If enable is there we are probably looking at a dead CPU or cracked balls/traces under it.

It could be a short on that line, but unlikely. What is diode mode on that line?
 
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protocold

Member
pin 25 on U7600 present (2.8v)

CPU_VTTSENSE_N is 0.8ohm to ground. Diode mode is 0.
CPU_VTTSENSE_P is 12.8ohm is ground. Diode mode is 10.

Is this not normal?

I decided to change the SMC, which seems to fix the intermittent PPCPUVTT_S0. It is now always 1.05v. Does SMC has anything to do with PPCPUVTT_S0?

Fan will startup slowly turn high, then low and then stay at high.

But now, I found out PLT_RESET_L is 0v. Diode mode 317.
 
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dukefawks

Administrator
SMC has nothing to do with that. Probably just the heat that affected something. But now that the SMC has been touched that is just another added uncertainty that probably wasn't necessary. Did you take an SMC from an identical donor board at least?

What is Ohm value on PLT RESET?
 
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protocold

Member
Yes SMC was taken from identical donor.

Ohm value of PLT RESET = 12.22K (it reads 12.22 on a 20K settings on my meter)

Further tracing lead me to CPUIMVP_PGOOD which is missing, therefore, PM_PCH_PWRGD is missing.

I measured R7403 and it was very low vs 5.1k compare to schematic and donor board.

So I replaced U7400 from donor board, now the fan start, stop, start, stop....
 
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dukefawks

Administrator
U7400 is never an issue, so you have introduced yet another variable that was probably not needed.
Usually CPUIMVP_PGOOD is missing because CPU Vcore is not present. The CPU needs to talk to U7400 to set the output voltage. So I still stick with my diagnoses of a bad CPU here. This board is most likely junk as CPU issues are just not worth fixing.
 
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protocold

Member
Just want to add more info, when I took off the old U7400, I found out that pin 22 (CPUIMVP_BOOT1) is blackened on both the chip and the board, looks like corrosion or burnt, all other pin looks fine.
 
2informaticos

2informaticos

Administrator
Staff member
Corresponding phase cannot work correctly if boost pin is no good.
Many times high-side MOSFET from that phase can get burnt, for this reason.
An overvoltage can occur and easy damage CPU...
 
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