820-3435 PPBUS 1.7v

rlowe215

Member
Working on a 820-3435 board

Have green light
PPBUS are only 1.7v. removed F7040 and PPBUS only have resistent of 10ohm. So not fully shorted.
 

JohnB8812

New member
Which pin is 10 ohms pin 1 or pin 2? If pin 1, inject voltage and see what heats up. If pin 2 check resistance between that pin and all the big coils to make sure no high side fets are short. Then, inject 1 volt to start into PPBUS to make sure none of the CPU fets or the CPU itself get hot first. Slowly increase voltage till short is obvious. Very common that one of the big tantalums fails on these.
 

rlowe215

Member
Pin 2 PPBUS_G3H thats 10 ohm.
Already tried inserted voltage, nothing getting hot with 1 volts
Strange thing is that my psu dont send out constant current before getting over 2 V. At 1.7v it draws 0.323 Ah. But over 2 V it sends out constant current but cant really find the short. A big part of the board starts to heat up slowly.
 

rlowe215

Member
yes I know but half of the board heats up just besides the cpu but cant find one component as I usually do. But how come ppbus is 1.7 and not 0v if shorted?
 

JohnB8812

New member
Are you saying just the CPU gets hot? If so, you had a short between VCore and PPBUS which is why PPBUS is 1.7 (VCore Voltage)
 

rlowe215

Member
Yes thats what I thinking of. Resistance to ground and 1.7V on PPBUS makes me thinking of that short. If I measure VCore and it also shows 1.7V should confirm it am I right?
 

JohnB8812

New member
Measure resistance between pin 2 of F7040 and the CPU coils. Also, remove the CPU heatsink to see if it is what gets hot first. I always recommend freeze spray for shorts
 

2informaticos

Administrator
Staff member
"check resistance between that pin and all the big coils to make sure no high side fets are short."
You should do this BEFORE inject voltage anywhere...

CPU coils have 10 ohms to ground too?
If not, check ALL other coils from the MLB.
Tell us which has the same valut to ground, as in PPBUS_G3H.
 
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