PP5V_S5= 0.31V A1466, Green light, no fan spin

Neil250

Member
820-00165

PP5V_S5 is not short to ground in diode mode

F7140: 8.60 PPBUS_G3H

U7501
4: 0 V
21: 3.38
23: SHORT

Changed U7501 with new chip, no change
Changed U7400, no change

CAPS: C7500 looks good but I removed i and short still there

Am I on the right track
This short is an issue keeping the board from starting but how to find this short

Change Q7520??
 
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2informaticos

Administrator
Staff member
"23: SHORT"
Any reason to change U7400?
That pin goes to PPBUS_G3H.

"F7140: 8.60 PPBUS_G3H"
Checked on pin 2?
If yes, then R5430 is bad, or has broken trace to U7501 area.
 

Neil250

Member
OK I was wrong, which means I f'd up the report above.

0V on pin 2 of F7140
Took out F7140

8.6 V on pin 1 when F7140 out
put it back, 0 volts and short to ground on both 1&2 of 7140
7140 has continuity
PPBUS_G3H is short to ground after the fuse

R5440 or U5450 pulling the G3H rail to ground perhaps?
Close look shows corrosion under U5450

ReplacedU5450, still short
 
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2informaticos

Administrator
Staff member
If you have short to ground on pin 2, the fuse is burnt.
Don't replace it, until eliminate the short.
Check ohm resistance of that short and compare with the value on the big coils.
 

Neil250

Member
Resistance

L7630: 280
L7430: 336
L7560: 60kO
L7520: 530
L7130: 1.4MO

L7310: 11O
L7320: 11O

L7701: 33kO

Voltage injection on pin 2 of 7140 fuse?
5V? 1A
 
Last edited:

2informaticos

Administrator
Staff member
Doesn't look to have any high-side MOSFET shorted.
If your readings are correct, then is safe to inject voltage.
Start with 1V and slowly increase, if needed.
If there is pure short, the culprit should show his face under 2V.
Set PSU current limit to max first.
 

Neil250

Member
Injected 1V

Q7520 gets very hot but when removed it, short remains
PIN 1 Q7520: 0.2 O to ground

Suspect PPBUS_S5_HS_OTHER_ISNS is short
 

2informaticos

Administrator
Staff member
"L7520: 530"
I don't see the reason for Q7520 to get hot; are you sure about L7520 reading?
Maybe heat comes from other close component.

Just in case, check resistance to ground on other pins of Q7520.
 

Neil250

Member
you were correct
repeated voltage injection 1.2 v
magic smoke C7540
replaced it and board works, short gone

Do you US boards to clean them up after working or just use an alcohol bath?
 

2informaticos

Administrator
Staff member
For local cleaning, use alcohol and toothbrush.
No reason to put entire board into US bath, for small area cleaning.
 
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