820-4924 charging problem

[Mike H]

I have an 820-4924 that came in with no power, not charging. R7020 was visibly burned so I replaced it along with C7091 which was dead short and appears to have been at least one of the problems. Now when I plug in the charger I get 16.5 volts on the PPDCIN_G3H_ISOL side of R7020, but only about 2.5 volts on the PP18V5_DCIN_CONN_R side. I have replaced U7100 but no change. PPBUS_G3H goes to about .7 volts when plugged in and then starts to drop while the probes are connected.

R7005 was blemished and measuring 15 ohms. I also replaced that and measured all other resistors in the area which tested good.

PPBUS_G3H .700V and dropping when probes are attached diode mode shows .124V

PPDCIN_G3H 16.5V

PP3V42_G3H 1.41V

PPVIN_G3H_P3V42G3H 2.14V

DCIN_ISOL_GATE 6.8V

PPDCIN_G3H_ISOL 16.5V


Logic board is very clean and shows no signs of moisture/corrosion. Any suggestions are appreciated.

 

[2informaticos]

First of all, welcome to the forum!

You must get correct 3V3_G3H first.
Check if R7020 is still good (47 ohm) and check diode mode to ground at C7090.
If low, remove C7090/2 (one by one) and check again; U7090 is the last suspect.
Don't fotget to check D7005.

 

[Mike H]

Thanks for the welcome and for assisting me with this issue. R7020 was in fact the problem and now I have a functional charging system! For some reason though, the fan does not work. I tested it using a power supply and it is definitely capable of spinning. PP5V_S0 is present at the connector as well as 3.3V on pin 4, FAN_RT_TECH. That lead me to believe that there was something possibly wrong with FAN_RT_PWM. Diode mode there shows .510V. Following that to Q6060 it seems that R6060 was a bit low. About 23k instead of 47k so I replaced it and when that did not change anything, I replaced Q6060. Still no fan. Since Q6060 gets data from the SMC is that the next place to look?

 

[2informaticos]

Do NOT touch fan circuitry.
It doesn't spin until CPU gets really hot on this model!