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iMac 820-3302-A Not turning ON

M

mushr00m

Member
Replaced PSU and same behavior

Dissambled board and noticed a lot of dust on it

Remove the USB ports protection and find oxidation on

C9415 and C9610

I tought it was them but with multimeter they are not short to ground

In the middle is C9487 which does not look bad not with oxidation but using the multimeter I found that this line (PP3V3_S5) is short to ground

What should I do next?
 
2informaticos

2informaticos

Administrator
Staff member
What is the exact ohm resistance of the short?
If low enough, voltage injection method should help.

First, inspect 3V3_S5 filter caps placed near the corroded area.
 
M

mushr00m

Member
ohm = 0.1

Tried to find injecting 2V on PP3V3_S5 on C9680 and looking and poruing some alcohol on U9610 and U9410 but didnt find anything, since I got an issue on these guys in the past

Not sure what do you mean by filter cap. Can you give me the number? Are it the small ones around U9610 and U9410?
 
2informaticos

2informaticos

Administrator
Staff member
Use boardview; look at the caps connected to 3V3_S5.
IR cam can help better than alcohol method.

BTW, remove CPU heatsink first.
And set amp limit to max on PSU, before injecting voltage.
 
M

mushr00m

Member
I am not sure what is filter cap... for me filter comes with F on schematics. I am used to iPhones one.

Since there are many caps connected to the 3V3_S5 and the NEAR area as you said is really TINY INY TINY LITTLE SMALLY

The pictures below are "NEAR" the corroded area.

Isn't that easy for you to confirm for me which one are those FILTER CAPS?

I do not have
 

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2informaticos

2informaticos

Administrator
Staff member
Usually, "F" is used for Fuses, not for caps.
We used "filter caps" to name the caps connected to a power rail.

C9480/81/87 and C9680/81/87 are the first suspects there.
 
M

mushr00m

Member
You right

However in Brazil we call fuses .... filters also... weird
and caps we always call it caps even though its function is to filter

The culprit was C9481. iMac is working 100%

Again not needed a IR cam.

You're also AWESOME!
 
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