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[SOLVED]820-3115 no cpu vcore

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roy.ruan

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logic board is 820-3115, getting all the power except CPUVCORE.

checked resistance to ground on r7515,shorted to ground. replaced the CPU IC , no short anymore,getting about 0.600 sth.
check r7441 (Since it's where the spilled was at) , it was 30 O, replaced and get 10 O.

power on but nothing change. checked Vron is there 3.3v. pin 46 29 16 all getting power. r7401 is fine.

then i replaced mosfet q7520 q7510 ,still no change.

don't know where to go now. any help please?
 
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roy.ruan

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thanks for the hint, i think i found the problem. pin 2 of r7441 to ground resistance is 670 sth. it's supposed to be close to 0 as i compare on the good board. that's why im not getting 7.7k between 2 and 3.

not sure if pin2 of r7441 had been corroded in the layers, it's directly connected to the cpu, i checked the none-stuff pin 1of r1361,it's connected to pin2 of r7441, but it's also getting 670 sth,not 0. so seems like the trace between the cpu and pin2 of r7441 is bad? but there is no place i can jump a wire
 
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roy.ruan

New member
FIXED!!! i removed the r7441 on the good board to check . found pin 1 was close to 0 and pin 2 is not reading. that means the pull down to 0 is from pin 1 not pin 2.
so pin1 is from the IC so , thought should be the IC, (that's actually the third one i replaced already) but anyway,i replaced another one. STILL DIDN'T GET CLOSE TO 0,
damn , then i was trying to get the schematics of MAX15119 and see the internal design and see why it's giving out 600 sth instead of 0. not available online.
i think once the chip is on , that pin should be pulled down. so I just jump a wire from GND to pin1 , pulled down that pin1 . damn then it worked!! now doing ASD on it

(I'm talking about pin1 and pin 2 of r7441,not the MAX IC)
 
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dukefawks

Administrator
You have now messed up the sense circuit for Vcore. If you want to ground anything it should be pin 2 of R7441, grounding pin 2 on U7400 directly may have unexpected effects.
Pin 2 of R7441 should go to the "local" voltage sense on the CPU and will be pretty much a short to GND
 
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roy.ruan

New member
But i removed r7441 on two good boards to check, after i remove r7441, pin2 is not 0V in diod mode, but pin 1 is, so I thought the "short to ground" side should be from U7400. that's why i grounded there.
I ran it the whole afternoon and no errors in ASD and OS running.
 
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