820-3476 with short on ppbus_g3h

SairFecht

Member
I've got a 820-3476 which is only showing 1v on PPBUS_G3H and about 300 ohms to ground.

There was corrosion around R1410 and R1617 which I've cleaned up and repaired during my first pass over the board, but apart from that it's clean with no other visible issues.

Pulled F7140 and showing 12.7v on pin 1 with a 155ohm, and 500ohm on pin 2.

Any suggestions on the best way forward?
 

2informaticos

Administrator
Staff member
Post EXACT ohm value to ground on both pins of R7202; red probe to ground.
Also check PPBUS_G3H value to ground removing U7501.
Be AWARE, do NOT power up the board without U7501!!!
Also check removing F7700 and Q3080.

BTW, post first diode mode to ground on PPBUS_G3H with black probe to ground.
Maybe you do NOT have any issue there...
 

SairFecht

Member
Post EXACT ohm value to ground on both pins of R7202; red probe to ground..

Pin 1 - 484ohm
Pin 2 - 475ohm

Also check PPBUS_G3H value to ground removing U7501.
Be AWARE, do NOT power up the board without U7501!!!

I'll come back to you on this.

Also check removing F7700 and Q3080.

I'll come back to you on this.

BTW, post first diode mode to ground on PPBUS_G3H with black probe to ground.
Maybe you do NOT have any issue there..

With black to ground this is open (checked on pin 2 of F7140)...
 

2informaticos

Administrator
Staff member
"Pin 2 - 475ohm
With black to ground this is open (checked on pin 2 of F7140)"
Then looks like good values.
If PPBUS_G3H disappears when solder F7040, you should have problem with some secondary supply.
Probably 3/5V, change U7501 for test.
 

SairFecht

Member
Yes, all tested OK, but it looks like my replacement U7100 might have been dead, I've swapped it again and we have fan spin. Need to test fully, but looks like it's OK. Thanks for your help!
 
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