820-2532 Green light on charger but won't power on!
I'm totally new to this troubleshooting logic boards lark but I've got a schematic, boardview, multimeter and a willingness to learn so here we go!
I got my hands on a Macbook Pro with an A1286 820-2532 logic board that charges the battery and shows a green light on the magsafe, yet wont turn on. when you press the power button the lcd screen kinda flashes black for half a second then nothing! I get no noises, fans, clicks, chimes; nothing. So after opening her up and removing the board I started troubleshooting, and here is what I've got so far and my thought process:
PPBUS_G3H - 12.56V
PPDCIN_G3H - Says it should be 12.6V yet I get 16.87V? Sounds reasonable though as I get power across the board (mostly)
PP3V42_G3H - 3.42V
PP5V_S3 - 0V - Board is in the S5 state though so this feels ok
PP3V3_S5 - 3.3V
PP3V3_S3 - 0V - Same again, not in S3 state
PP1V2R1V05_S5 - 1.12 - On the schematic is says 1.05V however in brackets it says "(1.1 for A01)"so I presume my voltage is fine?
When I short the power pads I now get 5.03V on PP5V_S3, and 3.3V on PP3V3_S3, which sounds good and explains why they read 0V earlier.
So what's the problem? I guess its something to do with the switch from the S3 state to the S0 state?
I take a look at the schematic and find the 3.3,5V S3 enable circuit and everything checks out fine.
I then find the S0 Enable circuit. So I test it (whilst in the S3 state):
MPCORES0_EN (forgot to write all the voltages down but I can get them if you need them to help diagnose the problem)
Then I check the other S0 rails section on the same page and I get:
No signal on U7780 pin 4 - ALL_SYS_PWRGD, this prompts me to check the inputs to the gate and I find no S0_PWR_PGOOD signal on pin 2.
So now I look for where the S0_PWR_PGOOD signal is made and it comes from U7201 pin 23.
So now at U7201 I check the VIN pin 16 and find PPBUS_G3H, I then look at pin 13 EN0 and I find 1.55V, however on Landrex it says "unconnected-235" , not too sure why. I also don't know if this voltage is correct.
I continue and check the ENTRIP 1 and ENTRIP 2 pins and find 0.7V and 3.32V respectively. Again I'm not sure if these voltages are correct or what exactly is going on, but something tells me that the ENTRIP 1 signal is wrong.
Also, on the "other S0 rails" section I tested R7892 and found 3.31V on pin 1 but nothing on pin 2, I then proceeded to test the resistance of the resistor and I read 2.8k rather than 10, not sure if this is the problem but this is the point I've reached and I don't really know where to go from here.
Some feedback on my thought process and your thoughts on my problem would be greatly appreciated :)
Is this a good question?