820-3302 - Short on PP3v3_S5

[gcain]

Measure PP3v3_S5 anywhere on the board in diode mode and I get 0.000. :/

I can't turn this board and see what gets hot, as I don't have the rest of the chassis, is there a way to calculate where the short could be?

 

[gcain]

So I built a little harness that works on my PSU.

Can see 11.40v hitting the board but it goes nowhere as PP3v3_S5 has a dead short, it even has continuity to ground.

 

[dukefawks]

So what do we do to a shorted rails to find a short?

 

[gcain]

Inject power!

Except I did that already and nothing heated up, that I could see anyway.

 

[Gurmon]

You could be unlucky and the short is INSIDE the board.

How much power did you put through the shorted rail ?

 

[dukefawks]

How much current was going in? Also did you put 11V on the 3V3 rail?

 

[gcain]

No, I didn't put 11v on a 3v rail, that sentence was worded poorly.

Picked up a new PSU as the other is really old. This one beeps and cuts out at 0.5v as if I'm shorting the terminals.


Edit: Buying a new desktop Power Supply. Seems the ones I have access too are rubbish.
Will report back once it arrives.

 

[gcain]

Took y our advice and bought a 10A supply.
Found the short in under a minute.


So now I get a green LED and nothing else. Shorting SMC_ONOFF_L does not get the fan to spin.

Not being familiar with iMacs I don't know if I can turn it on with no screen, button etc attached; so should it be turning on when shorting SMC_ONOFF_L at C600?

 

[dukefawks]

Where was the short? No screen needed.

 

[gcain]

Where was the short? No screen needed.

C9480 was glowing when I put about 3amps through it at about 0.9 volts.

 

[dukefawks]

C9480 is on 3V3_S4, how would that cause a short on 3V3_s5?

 

[gcain]

No Title

C9480 is on 3V3_S4, how would that cause a short on 3V3_s5?

It's definitely 3v3_S5 on my screen.

 

[dukefawks]

Maybe look at diagram?

 

[gcain]

Maybe look at diagram?

Look at what diagram?

It clearly says PP3v3_S5....

 

[dukefawks]

I only see a board view......

 

[gcain]

Yes, showing you the power rail on the right hand side.

 

[dukefawks]

Really???? How about opening the diagram PDF and looking at that......

 

[gcain]

Ha! You're actually right.
How can the Boardview say one thing and the diagram say another....

Either way, the short on PP3v3_S5 went way when I replaced that cap.

 

[dukefawks]

S4 and S5 are shorted together then? U7900 fucked?