iMac 820-2901-A not coming up

[Soji]

12v_s5=11.98v
Pp12_g3h= 11.98
Pp3v42_g3h=3.4v
Pp3v3_s5= 3.3v
Pp5v_s5 =4.8v
Pp3v3_s3=not present
Pp5v_s3= not present

u7700 on the other hand has
Vin pin 17 is 12v
En1 pin 12 is 3.94v
En2 is not present
Pmslp
Pls what can I do

 

[2informaticos]

Trigger SMC_ONOFF_L and check for pulse at P5VS3_EN.
If nothing, check for drop pulse at PM_PWRBTN_L.

 

[Soji]

Nothing happened

no Pulse

 

[2informaticos]

So PM_PWRBTN_L is stuck on 3V, no drop pulse noted?

 

[Soji]

No voltage on PM_PWRBTN_L
It’s 0.00 volt

 

[2informaticos]

You waste time, if don't post important information in your threads.
Don't you know yet which should be the PM_PWRBTN_L voltage?
Nothing can move on the board, if PM_RSMRST_L and PM_PWRBTN_L stay low; basic checkings...

You may have SMC problem.
Bad PCH can also pull down PM_PWRBTN_L.

 

[Soji]

Sorry this the first time am working on an iMac with such issues. And you are here to put me through, my experience is not that deep.
so I should change smc

 

[2informaticos]

Power on sequence is the same, no matters iMac, or MacBook.
You should take notes from the forum and gain time this way.

Check U4900 (3 OF 3) signals and voltages (page 45).