01521 PPBUS Short

[hambook]

I have an 820-01521 on the bench with a PPBUS_G3H short, 5v 0.01a on the charger. Getting 30 ohms on PPBUS, checked L7410, L7430, and L7210 and they aren't the exact same value but all are between 8-20 ohms, on a working board I'm getting 70 ohms. Does this mean the CPU is likely toast?

 

[2informaticos]

Check resistance (ohm value) between PPBUS_G3H and mentioned coils.
If the reading is the difference between mentioned values, then bad chip on CPU power supply.
If you get the sum of them as reading, the problem is not there.

BTW, check resistance to ground on all coils of the board first; any gives 30 ohm?

 

[hambook]

Sorry, double checked and my PPBUS is actually 2.4 ohms. But the resistance between the mentioned coils and PPBUS is the sum of the two of them to ground, so onward.

No coils on the board give 2.4ohm resistance. Would my next step be to inject a small amount of voltage into PPBUS?

 

[2informaticos]

Did you check on L9060 too?

 

[hambook]

Yeah, L9060 is around 4.2K ohms

 

[2informaticos]

Then is safe to use voltage injection method.