820-3437B - Not turning on, no fan spin

mushr00m

Member
820-3437B

Not turning on
No fan spin

All the main rails are present

The only weird stuff is

PP1V05_S0 and _SUS which are supposed to be 1.05V and both lines are 1.40V
 

mushr00m

Member
Just measured on C7648 and its 1.42.

But the funny thing is that right now it made the RAM BEEPS after pluggin the cord. It didnt happen before!
 

2informaticos

Administrator
Staff member
You may have a problem with RAM, or CPU.
1.42V at C7648 is too high; there could be problems on U7600 area.
Check all surrounding components; pay atention to R7611/12.
 

mushr00m

Member
I already replaced U7600 and the resistors are R7612 = 40K AND R7611 = 30K on the multimeter measure on another board and gave me the result to be honest. I think they are good... Should I try to reflow the RAM one more time?
 

2informaticos

Administrator
Staff member
1.42V is high too much there!.
Such value can only be caused by faulting components, or corrosion.

Anyway, you can try to adjust the correct voltage playing with mentioned resistors.
Someyime Apple provides a formula for output voltage, based on feedback resistors.
Check page 49 to make an idea; 3V42_G3H generation, as example.
 

mushr00m

Member
1.42V is high too much there!.
Such value can only be caused by faulting components, or corrosion.

Anyway, you can try to adjust the correct voltage playing with mentioned resistors.
Someyime Apple provides a formula for output voltage, based on feedback resistors.
Check page 49 to make an idea; 3V42_G3H generation, as example.

Yeah I know its too high

I check all the components around U7600 and replaced U7600 twice.. Still no result

I found Q1920 missing on the board replaced and still same behavior. Not sure if without would make a difference

Not sure how to try to adjust voltage with the voltage dividers you told me. Would you replace those voltage dividers according to the results on the multimeter being barely different of the schematic?
 

2informaticos

Administrator
Staff member
Did you see the formula in page 49???

Q1920 related resistors are good?
Do you get VTT/REF from U7400?

BTW, any reason to quote an entire post visible few centimeters above?
Please maintain forum aesthetic...
 

mushr00m

Member
Put back Q1920 and a cap that was missing now I do get back to 1.05v ON PP1V05_S0... Still no FAN SPIN and CPU gets HOT
 

mushr00m

Member
This one was water damaged to be honest with you and went to another store... I am carefully inspecting it and now it doesnt appear as has more components off

I just found its missing C7570 / C7541

However I think they would not be the cause to turn on
 

mushr00m

Member
Weird mannnnn

Now it turned ON..

No chime...

The system is loading however it seems to be LOADING so slow...

Still no FAN SPIN

It's taking too long loading the system. I will be waiting however already sent this message
 

mushr00m

Member
It bring really slow to the password recovery screen... Tried reset SMC

Reset PRAM seems to be not working...

I think there is a sensor issue also
 

2informaticos

Administrator
Staff member
Glad to hear it works.
Didn't expect to solve it, being sent out from other service.

Please let feedback with the solution.
This can help other members in the future.
 

mushr00m

Member
Actually it was missing a cap around U7600 and I didnt notice it at first. Then put two more caps C7540 and C7570 and tried to check USB activity as you told me and the machine was working. I got surprised also
 
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