820-3588 (imac) - pp3v3_S5 shorted

[MUUK]

iMac 21" 2013

no power.
no lights on MLB
Tried known good PSU same result.

Found that pp3v3_S5 has a dead short to ground.
Seems to be on pin 1 of L7610 (0v diode mode)
Pin 2 of L7610 is 0.125v

Tried injecting some voltage got to 3amp @ 0.7volts

Not done many iMac boards so am unsure as to how much current i can put in this rail, or if there are any common issues on these
Thanks again.

 

[dukefawks]

You can inject 3V, but it is better to monitor current and once 1-2 watts are going in something should heat up. You had 3x0.7=2.1W flowing into the board so there should something be heating up. Could be any cap on that line really. Worst case would be the PCH/CPU.

 

[MUUK]

Thanks Duke, it is U1100 that is getting hot unfortunately. One for the parts pin. Thanks for confirming.