A1286 820-2850 missing PP1V05_S0

[roy.ruan]

having this 820-2850 board, fan spins but check no CPUVOCORE.
traced down and found PP1V05_S0 is missing

think CPU vcore won't come out if PP1V05_S0 missing.

checked on U7600, pin 13 14 =5v, pin3(en)=3v

all look good, but no output PP1V05_S0, then replaced u7600 and Q7630 Q7635
but no change.

any advice?

thanks

 

[aprendiz]

Resistance to ground on L7630??

 

[roy.ruan]

diode mode 0.014
resistance mode 21.2 oh

 

[dukefawks]

Check R1305/06 and traces to U7600.

 

[roy.ruan]

R1305=0 oh R1306=0 oh ( schematics says 10,but i checked on another working board,they are all 0 too)
traces to resistors connected to U7600 are all good

and idea?

 

[dukefawks]

No idea. Badly soldered U7600 or bad CPU, the CPU is supplying the feedback in this circuit.

 

[roy.ruan]

already replaced U7600 ,so.. only thing left is the CPU?
ever try to reball this model with success?

 

[dukefawks]

And what makes you thing U7600 replacement was successful? Replacing CPU is a waste of time.

 

[roy.ruan]

it was pretty easy to replace... and i replaced twice U7600 already

 

[dukefawks]

Not much left then besides a dead CPU. Check the coil and cap just to be sure, but they never fail.

 

[roy.ruan]

No Title

IT IS THE CPU. hate doing it, but no other way around when I have to get the job done.
pull the CPU from another bad board, reballed and soldered on , spent almost an hour on it then it works now. testing it.

 

[roy.ruan]

thanks again man, appreciate the hint