820-3437 Power on issue

tlough75

Member
I have on the bench an 820-3437 with a power on issue. The customer told me that it would charge but not turn on so they replaced the battery. They said the owner used it for a bit but it started acting up so they replaced the battery again. I measured the G3H rails with only battery plugged in and it has those but when I trigger SMC_ONOFF_L and measure voltage on pin 7 of U5110, the voltage drops then recovers when I release the power button as I think it should. SMC_RESET_L behaves the same way. sits at 3.3V until the power button is pressed, drops to .4V then recovers once I let the button go, but the computer will only turn on when I plug MS in. The laptop will shutdown with the power button pressed but will not come on. I attempted an SMC reset but no change. Is it safe to say I have an SMC issue? BTW there are no signs of liquid damage, no corrosion or anything. I will check R5116 and R5100, as well as R7100. I see that SMC_RESET_L also goes to J6100 but. I didn't see anything there.
 

2informaticos

Administrator
Staff member
Looks like power button acts as SMC reset in fact.
Disconnect trackpad flex and try R5115/16 pads instead.

With trackpad connected, post all U5110 voltages.
I bet for low level at pin 6...
 

tlough75

Member
You were correct sir.


U5110 (W/TPAD)
1: 3.42V
2: 0V
3: 3.42V
4: 2.8V
5: 3.38V
6: .567V
7: 3.41V
8: 3.3Vv

U5110 (No TPAD)
1: 3.42V
2: 0V
3: 3.42V
4: 2.8V
5: 3.38V
6: 3.4V!!!
7: 3.41V
8: 3.3V

So it must be either the TPAD or the cable. Time to play a little "process of elimination". Thank you for your guidance.
 
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