820-00045 12" Retina PPBUS_G3H is 20v

[osmun38]

PPBUS_G3H is 20v, and I've narrowed it down to the u7100 chip because that is where it gets created, but the schematic is very confusing. It's getting power because it's letting power through, but I can't tell if its a buck converter afterward or the chip itself. The schematic is very confusing PAGE 43 which I'll include but I don't know where to check now.

There has been no history of drop damage or water. But when opened by my colleague he ripped the cables on the machine I replaced all of the cables and the original problem was that the keyboard wasn't working now trackpad doesn't work either.

 

[JohnB8812]

Likely have 20 volts because Q7110 is shorted. Replace it Q7120 Q7155 and U7100 all at once and see what happens

 

[2informaticos]

Both Q7110/20 shorted on high-side MOSFET...
Confirm that posting ohm value between R7120/50.

 

[osmun38]

Resistance between R7120 and R7150 is 113 KOhms

 

[osmun38]

Now its not even getting 20v

 

[2informaticos]

And what voltages do you get on that board?
Any short on power rails?

 

[osmun38]

PPBUS_G3H = 4.6v
it only has 147 OHMS of resistance

 

[osmun38]

Could that be a short from the chip

 

[2informaticos]

Post diode mode reading on F7140; both ways, red and black to ground.
Do you really get 4.6V there?
If Q7110/20 are good (are you sure?), then bad U7100...

 

[osmun38]

Red on ground = 203
black on ground = 212

Yes PPBUS_G3H = 4.6V
How do you check if Q7110/20 are good ?

 

[2informaticos]

Check them (diode mode) between D-S; all 4 MOSFETs (two pairs).
Only high-side ones are suspect there, but check all.

 

[osmun38]

Q7120 Diode = 205
Q7710 Diode = 445

 

[2informaticos]

To specify, Q7110 and Q7120.
Did you check to ground, or D-S for each MOSFET?
I expected 4 readings...

 

[osmun38]

Sorry that was to ground
I think this is right
Q7110: S1/D2 --> D1 = 0
Q7110: S1/D2 --> S2 = 472

Q7120: 1 --> 4: 636
Q7120: 1 --> 6: 634

 

[2informaticos]

"Q7110: S1/D2 --> D1 = 0"
Exactly what I told you; hgh-side MOSFET of Q7110 is shorted.
So change Q7110.

 

[osmun38]

Waiting on board from China.
I took q7110 off of the board and it didn't get rid of the short on PPBUS_G3H still have around 140 Ohms

 

[2informaticos]

"PPBUS_G3H still have around 140 Ohms"
Is that ohm scale, or diode mode with red probe to ground?
If diode mode, check if you get OL with black probe to ground.
If yes, change Q7110 and test the board.