820-2936 Macbook Pro - Not turning on, no fan spin, but CPU gets hot

[Polymer15]

Hey guys,

Have a 820-2936-B Macbook Pro here with some frustrating issues. We get a green light on the AC adapter however, no fanspin/chime, and the CPU and GPU start to get hot (could be due to lack of fan spin?)

Checked all of the voltages, the only outlier is PPVIN_SW_T29BST, which is 2.82V. (see attached image for all voltages)

From this I checked Q3880 as this seem to be where it's made, PPBUS_G3H is a steady 12.6V and the gaet for Q3880 is 12.2V. At the drain of Q3880 however, the voltage is a meager 0.3V. I replaced Q3880 to no effect.

Diode mode to ground at drain of Q3880 is 0.4V (only works with negative on component, positive on ground? I've not noticed this with other components when diode checking, or maybe I'm going mad), resistance is 100kohmn (slowly goes down),

Consequentially, PP15V_T29 is 0.32V

Plus, I am going to assume that PP5V_S5 is supposed to be 5V given the name, my schematic shows 3.3V however so for consistency, I still put 3.3V.

Help would be appreciated!

 

[JohnB8812]

Ok so do you get a light on a USB mouse when you plug it in?

 

[Polymer15]

Didn't expect that question! But, yes it does power USB devices it seems

 

[JohnB8812]

Ok plug in a known good LCD and see if you get anything on the screen. Shine a flashlight through the Apple logo to see if you get a blinking questionmark folder. Also seems like you got a bad fan.

 

[Polymer15]

Definitely not a bad fan, replaced the fan and still having the same issue. I don't have a spare screen to hand so cannot test, however there is no question mark folder when shining a light through. Also as I said, there is no chime. If the display was just not working, there would still be a chime

 

[JohnB8812]

CPU VCore Present?

 

[dukefawks]

It powers a USB device....it was asked if a USB mouse would light up the LED.

As there is not fan spin ALL_SYS is probably not present. Check all power rails for the missing one.

 

[Polymer15]

Will test VCore shortly, but yea duke as said above, PPVIN_SW_T29BST is 2.8V where it should be 12.8v

 

[dukefawks]

You are measuring Thunderbolt voltages which have nothing to do with the board booting or not.

 

[Polymer15]

Apologies duke, PPVIN_SW_T29BST was in the "always present" set so I assumed it should be there. Just checked all CPU Vcore voltages and I got the following:

PPVCORE_S0_CPU 1.16v
PPVCORE_S0_AXG 0
PP1V5_S3_CPU_VCCDQ 1.5
PP1V05_S0_CPU_VCCPQE 1.06
PP1V8_S0_CPU_VCCPLL_R 1.79


I did just test with another mouse and it's a bit odd, the light for the mouse (as in the back light for the scroll wheel, not the laser) flicks on when plugging into power but turns off after a split second. The laser light doesn't come on at all.

 

[dukefawks]

Vcore is present at 1.16V so there must be fan spin. But the 1.16V would indicate it is brain dead as normally it will drop down from 1.16 to under 1V.

Any history on this board?

 

[Polymer15]

History is liquid damage, had wine spilled on it and the customer used it until it died - only lasted for a day. Not even moderate signs of liquid damage to be seen, there are a few dirty pads but I've cleaned them up and they have good connections.

 

[dukefawks]

Board is brain dead and it could be anything. Give the board a good clean first if no real corrosion is evident. Crap under the SMC is very likely.

 

[Polymer15]

Will remove the SMC and see if there is any crud, hopefully none has gone under the CPU

 

[dukefawks]

Dont, just some flux and heat first to try and clear the crap. Ultrasoniced the board?

 

[Polymer15]

Absolutely immaculate under there! Not a pinch of crud. Have reballed/resoldered every component on the board that has a whiff of suspicion regarding it's corroded-nes. I would ultrasonic clean it, unfortunately I don't own a UC. Seems that we're getting to the end of our tether with trying to solve the issue here.

Any tips for doing a good clean without an UC?

 

[Polymer15]

Have cleaned everything as best as I can, re-soldered the dodgy pads, and now we actually get a fan spin (yay). Could have either been a dodgy connection to the fan, or something completely different. Currently re-checking the voltages to see if anything has changed.