820-2936 No power, weird issue

tlough75

Member
So I have on the bench an 820-2936 tonight and It has me stumped. With board only out on the table, when I plug in a MS I get no PP3V42 but has a light, PPBUS_G3H is 2.6V. On U6990 I'm getting 18v on pins 4 & 7, but no PP3V42_G3H. I replaced U6990 and at first it seemed to work, had MS light, PP3V42 was present as well as PPBUS. After a few min I tried to turn it back on and nothing. Just a fading green light. It seemed like I fixed it but not back to not working. I tried to trigger SMC_ON/OFF_L but nothing happened.
 

tlough75

Member
U7000:

1: .004V
2: 18.25V
3: 4.38V
4: 4.38V
5: 0V
6: 0V
7: 0V
8: 0V
9: 0V
10: 0V
11: 0V
12: 0V
13: 0V
14: 0V
15: .142V
16: 0V
17: .773V
18: .751V
19: 5.1V
20: 5.1V
21: 0V
22: GND
23: .672V
24: .672V
25: 4.79V
26: 17.83V
27: 18.1V
28: 18.1V
 

tlough75

Member
So weird. I got PP3V42 and PPBUS to show up for a min, then it went away again. Also, the magsafe light fades away until I turn off then turn back on the power supply. Even when they showed up temporarily, no fan spin. I'm wondering if maybe something is pulling it down. Or if the SMC is bad.
 

tlough75

Member
Confirmed all pins around U6990 are connected to the vias around it and touched up solder joints. What other components around it could influence it not to put out PP3V42_G3H?
 
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