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820-2915 ppbus_g3h short

K

Kyle93

Active member
Have a 820-2915 that already has a new 2017 GPU before I received it. Has a power problem with PPBUS_G3H. When R5410 is soldered I have short on PPBUS_G3H with no fan spin but when it is removed short gone and board powers up but no video. Tried replacement R5410 but no change

Can this be caused by shorted GPU since R5410 is on GPU power rail?
 
K

Kyle93

Active member
Replaced Q8950 and short still remained. Removed GPU and short was gone.

Replaced GPU from SEE-IC and short returned.

Is short inside the board at this point??
 
2informaticos

2informaticos

Administrator
Staff member
How can be the short inside board, if disappeared when you removed the GPU?

L8920 has very low value to ground because of GPU; this is normal of course.
But such low value is practically short on PPBUS_G3H, when Q8950 is shorted D-S.
 
K

Kyle93

Active member
replaced Q8950 and Q8951 and short was gone. board powered on for a few seconds and turned off again. Short returned. What to try next
 
2informaticos

2informaticos

Administrator
Staff member
Q8950 got shorted again.
Replace Q8950/51 and U8900 at same time.
Be sure C8956 is OK; check its traces.
 
K

Kyle93

Active member
Replaced Q8950/51 and U8900 at the same time and short returned as soon as board powered up.

C8956 traces good
 
2informaticos

2informaticos

Administrator
Staff member
Which is the exact value of that short, on the GPU core rail?
004-009 on diode mode is normal for that board, I think.
A pure short there could kill Q8950 once powered up, and same short will pass through it untill PPBUS_G3H.
 
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