Low PPBUS G3H voltage

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PPBUS_G3H is one of the main rail on a MacBook that needs to be present in order for the computer to turn on, since nearly every rail on the computer uses PPBUS_G3H to get their required voltage, whether via boost converters or buck converters. Sometimes, one will see a MacBook with a PPBUS_G3H Voltage of 8.1~8.2V/12.1~12.2V on an Air/Pro. Normally, PPBUS_G3H voltage on an Air and Pro should be 8.5~8.6V and 12.5~12.6V. This is due to SMC not being powered on to boost PPBUS_G3H voltage to 8.5V/12.6V. This could mean either of these things:

  • One of the tantalum capacitor on PPBUS_G3H is shorted and needs to be replaced.(( if there is a shorted capacitor then it would be outright 0V on PPBUS , but not be the case. of a leaky capacitor , I will however allow Louis or someone else to confirm this. One thing I can confirm is , when a short to ground is present the above PPBUS voltage will be much lower than the base of 8.1~8.2V/12.1~12.2V)).
  • Motherboard's SMC is turned off because it's not getting it's power. Check SMC_RESET_L
  • ISL chip can't communicate to SMC because one of the data lines is shorted/disconnected (SMBUS_SMC_5_G3_SCL/SDA)
  • Your SMC is toast and needs to be replaced.