820-3023 fan spins for 1 second then pauses for 5 seconds

[galvestonmac]

I have an 820-3023 with liquid damage that will not start up. Corrosion was found at U6100 and cleaned. Voltage at Y2705 is 1.14v when power cycles up.
Green light on charger, PPBUS_G3H 8.6v

When power is plugged in the fan spins for 1 second then stops then starts again 5 seconds later.

Diode mode to PPVCORE_S0_CPU shows short. Any hope with this or should I not bother?

 

[JohnB8812]

What is your resistance to ground on CPU VCore? Doubt it’s shorted it’s a low voltage rail. Anything and everything can cause this first spot to check would be if JTAG is corroded and what you get on PPVRTC_G3H.

 

[galvestonmac]

Diode mode measurement PPVCORE_S0_CPU=.46 ohms
PPVRTV_G3H=3.3V

Nothing that I can see on JTAG. I put it in the ultrasonic tank and cleaned it thoroughly with alcohol and a toothbrush as well.

 

[galvestonmac]

On R7086 I get a steady 6.81v on pin 1. On pin 2 I get 0v. Resistor checks out as 330k with meter. Not sure what I should be getting at pin 2 for voltage.

 

[galvestonmac]

I've also checked out R5110, R5111, R5112, etc. R5121-R5128 and they all check out with correct readings. Steady 3.3v at R6101 even during power cycling.

 

[galvestonmac]

PPBUS_G3H=8.40v

PPDCIN_G3H=17.8v

PP3v42_G3H=3.42v

PPRTC_G3H=3.42v

PP5V_S5=5V

PP5V_S0=4.6V TO .03V RANGING

Removed and resoldered U6100

 

[JohnB8812]

8.4 volts on PPBUS would indicate some kind of issue around the SMC. Check that again if you can may be crap under the SMC if it’s 8.4. If PP5V_S0 is pulsing then it’s trying to turn on but can’t. Is CPU VCore pulsing as well?

 

[galvestonmac]

Thanks. I'll check PPVCORE again to verify. I believe that it was steady.

 

[dukefawks]

Need resistance to GND on PPVCORE_S0_CPU, not diode mode. U6100 may have gotten corrupted, try another BIOS for testing but make sure to keep the old one.

 

[galvestonmac]

Resistance to GND for PPVCORE measured at C1681 is 26.6 Ohms. Will check out U6100 closer