820-2936-B Liquid damage Green light CPU heats up

wrbailey

New member
I have a 2011 820-2936-B board which had liquid damage.

Cleaned the board and I now receive green light (and amber when battery present) but no fan.

The heat sink gets hot.

I've tested all rails. Only ones I am missing are the PP0V75_S0_DDRVTT (Measures 0.005 V)



PP1V05_S0 (0.67V)

The CPU is getting warm and I have the 5V S0 rail going to the fan.

So if I am correct, the computer is turning on, but is missing some S0 rails??

I checked the rest of the S0 rails and it is just those two I am missing.


For the PP0V75_S0_DDRVTT I checked U7300 and I have the 5V S3 and 1.5V S3 going into the chip.
I also have DDRREG_EN measuring about 3.3V, however I have 0V at MEMVTT_EN at pin 17 (which is noted as VTT_EN in small print next to PIN)

When I jump over to what creates MEMVTT_EN I have PM_SLP_S3_L and it measures 3.27V and I have 4.97V at MEMVTT_EN_L and R3210 measure 9.97kohms.



Am i running in circles here trying to figure out the PP0V75 or should I be trying to figure out 1.05V S0 instead? Or would fixing the PP0V75 help fix the 1.05 as 0.75V is higher up on the voltage rail list?

Thanks for any help!!
 

wrbailey

New member
Enable on pin 3 (I'm not home to confirm, but) measured 0.556V

Looking at the specs of the chip, HIGH must be 1.1v or higher.
 

wrbailey

New member
I'll check, but I believe PM_SLP_S3 (we may be talking about a different EN signal on different packages) was not missing. Having a very active 20 month old, sometimes a few days go by before I can touch a board again.
Thank you for the help. I should be able to do more measuring/confirming values this evening.
 

wrbailey

New member
Yep, I was not looking at U7600 for PIN3. I will measure that EN signal this afternoon when I get home and see if it is HIGH and if it is replace u7600 and see if it fixes my issue.
 

wrbailey

New member
I got home and cleaned around the u7600 IC and let it dry. I then plugged the charger in and I get a 1 second fan spin instead of No fan spin. The EN at pin3 goes from 0v to up to it seems around 3.3v and then back down to 0v, while the fan is doing its 1 second cycling off and on. What would cause that? I hear Q7630 being bad usually along with U7600... How do I test if Q7630 has gone bad?
 

wrbailey

New member
It is for a split second, just like the spinning of the fan. It is 0V and then goes up to about 3.3v and then back to 0v, all with the cycling of the fan
 

wrbailey

New member
I was trying to take some diode measurements of Q7630 and looking at the package on the board, there are 4 pins on the bottom and 4 pins on top. On this "bad" board I get (from left to right) 0, 0, 0, 0.446 and then on top I get 0.450ish, 0.450ish, 0.450ish and 0

On a known good board (only needs it's LCD connector replaced) instead of the 0 diode measurement on the top right position, I get 0.550 diode measurement. Don't know if this means the Q7630 needs to be replaced? I was going to replace it when I got back home from work, but any insight would help.
 

wrbailey

New member
Replaced Q7630, which removed the short to ground at PIN1 on Q7630. However now I plug the charger in and the fan doesn't spin anymore. If you stare at the fan, you will see it kind of barely "wiggle" constantly.

It does look like there is still a short to ground on PP1V05_S0 as both sides of the inductor in that circuit (at work can't remember if it actually labeled L7630) are showing a short to ground, diode measurement of 0.000 and 0.002. I plan on removing the inductor and seeing which side the short is on. At this point I would almost guess it will be on the computer side (not the side to the left of the inductor)

If I find that the short is on the right side, if I place 0.5v at the inductor pad, something should get warm, correct? I also wouldn't want to go higher than the 1.05v, correct, since I believe this goes to the CPU or GPU?

Thanks for any feedback!
 

wrbailey

New member
Well I guess if it is then there will be no more harm done by placing some voltage to the inductor pad... guess we'all see if something besides the CPU is the cause of the short...
 
Top