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820-3023-A Liquid damage. No PPVCORE_S0_CPU_REG or _AXG_REG

Paul Daniels

Paul Daniels

Super Moderator
Prior repair. Liquid damage. Arrived with no fan spin. Repairs to corrosion on U7600, replacing R7981, reconnecting trace between U7600 and C7981 (CPUVCCIOS0_EN) restored fan spin.
No chime.
No LCD_EN.

I now have no PPVCORE_S0_CPU_REG or _AXG_REG out of U7400.
U7400:1 EN (CPUIMVP_VR_ON) is present.
U7400:2 TON is ~0.1V and PPVIN_S0_CPU (~8.5V) is present on the other side of R7402 but would appear to be pulled low by TON (checked and replaced R7402, there is continuity to U7400:2
 
D

dukefawks

Administrator
U7400 needs communication with the CPU so pretty much anything can cause no Vcore. Could be crap under SMC/CPU or dead CPU even. This will suck....
 
2informaticos

2informaticos

Administrator
Staff member
"U7400:2 TON is ~0.1V and PPVIN_S0_CPU (~8.5V) is present on the other side of R7402"
Pin2 should drop to 0.5V aprox when CPU power supply works.
If doesn't work, pin2 should go back to 8.5V.
0.1V could point to bad U7400; did you change it?
 
Paul Daniels

Paul Daniels

Super Moderator
2informaticos said:
"U7400:2 TON is ~0.1V and PPVIN_S0_CPU (~8.5V) is present on the other side of R7402"
Pin2 should drop to 0.5V aprox when CPU power supply works.
If doesn't work, pin2 should go back to 8.5V.
0.1V could point to bad U7400; did you change it?
Click to expand...

I did, same outcome. I would have liked to had access to a data sheet on this because it'd be interesting to see if the chip uses the TON pin as a status indicator too (ie, pulls it low to indicate a fault).
 
2informaticos

2informaticos

Administrator
Staff member
Look the datasheet for other buck-converter controller chip.
Many have the same TON pin and you will see it has totally different function (it is not output at all).
 
Paul Daniels

Paul Daniels

Super Moderator
Would be nice to have a working reference. No donors of this model on hand, awaiting supply. I agree the TON pin voltage is a bit strange, unfortunately without a comparison on hand I'm unable to ascertain if that's normal or not for this model ( but yes, it's a flag in my mind ).
 
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