iMac 2017 21.5 820-00597 Logic Board Will Not Power On

2informaticos

Administrator
Staff member
"1.0V for PM_PGOOD_FET_P1V0_S3 on R8410 Pin 2"
That's no good; check if R8410 has 10K (measure it out of board).
If really good, try changing U8500.
If still the same, change U8410.
 

ideachief

New member
Alright, I checked R8410 off the board and it came in at ~10K Ohm like it should. So I replaced U8500 as recommended and now I get 3.3V for PM_PGOOD_FET_P1V0_S3. However, the board still won't power on. Should I replace U8410? I suppose I can go back and recheck all the other voltages.
 

2informaticos

Administrator
Staff member
Don't tocuh U8410!
Don't you have correct 1V0_S3 on its pin 8?

Post again voltage on all U8500 above mentioned pins.
 

ideachief

New member
On U8410 Pin 8 I have 1.0V. The voltages for U8500 are: Pin 1: 3.325V, Pin 2: 3.322V, Pin 3: 3.325V, Pin 4: 3.325V, Pin 5: 3.325V. Pin 6: 3.325V, Pin 8: 3.271V, Pin 9: 3.325V, Pin 10: 3.319V, Pin 14: 3.326V
 

2informaticos

Administrator
Staff member
U8500 looks good, so you must have voltage on various coils of the board.
Do you get 12V output now from Q8450?
 

ideachief

New member
I get 0V output on Q450 (Pins 1, 2, 3). I also have 0V on FET_EN_P12V_S0 (Pin 4). I do get 12V on PP12V_G3H_P12V_S0 (Pin 5).

Just in case it helps, U8450 voltages are as follows: Pin 1: 11.97V, Pin 2: 1.77V, Pin 5: 11.97V, Pin 6: 0V, PIN 7: 0V, Pin 8: 0.051V. On R8542, Pin 1 has 3.3V (Pin 2 is connected to U8450 Pin 8).
 

2informaticos

Administrator
Staff member
"U8450
Pin 2: 1.77V"
You've said to have 3.2V on pin 8/U8500; confirm that.
If yes, check the components in between.

Q8450 is classic failure, you can try changing it directly.
May need to change U8450 also.
 

ideachief

New member
Alright, looks like the issue was U8450. I replaced Q8450 but it didn't fix the issue until I replaced U8450. Hopefully this is all that's going to be needed. Should I check or replace any other components?
 
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