iMac 820-3126 Half Fan Spin

mushr00m

Member
Got it. I will assemble this machine however why did you get to U7700? I would like to understand more about the logical process so I can do it more by myself.
 

mushr00m

Member
Got it

ANYHOW

Replaced the IC

Didnt assemble into the iMac but only plugged the PSU cable into the board and put into the power cord

STILL

Only LED 1 working

Tried again to trigger SMC with tweezer on that cap I mentioned above and same behavior

ONLY LED 1 WORKING
 

2informaticos

Administrator
Staff member
Did you test with its PSU?
Did you connect both cables between PSU and MLB?
Do you get 12V_S0 when trigger SMC_ONOFF_L?
 

mushr00m

Member
Yes tested with its PSU
What do you mean by BOTH cables? Only connected J600.
I didnt measure 12V_S0. I expected the LED 2 to get working as I replaced U7700
 

2informaticos

Administrator
Staff member
"Do you get 12V_S0 when trigger SMC_ONOFF_L?"
Take your time and tell us if you get it; check for pulse at least.
 

mushr00m

Member
Just measured PP12V_S0

Actually

Its around 0.500V and then it tries to go up sometimes it shows 8V / 9V and then back to 0.500v in loop.

That's the behavior.

Didnt even tried to trigger SMC_ONOFF_L after seeing it. I guess it needs to be stable in order to work.
 

2informaticos

Administrator
Staff member
SMC_ONOFF_L must be triggered for short time only, like pressing power button.
PS_ON should go low at same time.

When 12V_S0 tries to appear, check for pulse at big coils and ALL_SYS_PWRGD.
Be sure no short on any coil...
 

mushr00m

Member
Yes when I trigger SMC_ONOFF_L I use a tweezer on both sides of the cap I mentioned above. Is it the correct way? If not please detail how to do it properly.

PS_ON = 3.96 for some seconds and then goes to 0 and then back to 3.96
ALL_SYS_PWRGD = 0.030v and then goes to 0V and then tries to go back
12V_S0 = Its around 0.500V and then it tries to go up sometimes it shows 8V / 9V and then back to 0.500v in loop.

L7100
PIN 1 = Same behavior as 12V_S0
PIN 2 = Same behavior as 12V_S0
 

2informaticos

Administrator
Staff member
In my opinion, is more convenient to solder a wire on corresponding pad os S5010 and touch any metal placa to simulate power button.
This way also helps you to test starting in SMC bypass mode.

I didn't see any mention about output voltages from pages 68, 69 & 71.

Trigger SMC_ONOFF_L more times; helps to catch higher pulses...
 

mushr00m

Member
Thanks for the advice however still prefer to use a tweezer.

To measure the outpages on the pages you requested Its on the other side of the board I will probably need to measure it with PSU lab. Is that OK? Since you told me it doesn't put 12V_S0 to work?
 

2informaticos

Administrator
Staff member
You can't test the board without 12V_S0.
You can try to make a bypass from 12V_S5 to 12V_S0.
This may not work, if PCH timing is not respected, for power on sequence.

Use a spare iMac PSU, to work on the desk.
You don't need to connect internal LCD, nor speakers.
 

mushr00m

Member
Did a jumper between PP12V_G3H and PP12V_S0

Inject 12V using PSU LAB

Output from pages you requested (pages 68/69/71)

68
R7420 = 0V PIN2/4

69
C7510 = 0V

71
C7835 = 1.5V

Whats next?
 
Top