XFX R9 380 No Ram Voltage.

[saronno]

Hi, I am trying to repair this R9 380 by XFX.

Fans works, no video .... but it's not the gpu ... there is no voltage
on the ram.

Looking at the board, there are two APW8722 near the two PCI-e power connector.

Checking the datasheet, there are two interesting pins: BOOT and COMP.
If COMP is pulled down, the IC shut down.
The BOOT honestly I am not sure, but it should give a voltage bump at
the beginning to initiate the voltage regulation.
VCC is presente. The two MOSFET connected to the IC are good.
There are not evident shorts checking here and there with the multimeter .. and also checking with a finger if something is hot results in nothing obvious.

Any idea? I was guessing the APW8722 was faulty but since both of them have the same behaviour I am inclined to think there is something else who stop them to regulated the voltage, maybe pulling down COMP ...

At the beginning I also guessed there was something wrong with the bios but I check the chip with my ch341 and the bios was ok ... but there is no voltage to the chip when you star the board !!

Photos of the board.
https://imgur.com/a/Drf2g6L

[saronno]

Finally I have some spare time to keep analyzing this board.
It seems the problem has nothing to do with the APW8722.
I check the pci-e voltage and both of them are presente (12v and 3.3v).
But GS7103 near the eprom has a very low VCC. So I find what component
is responsible for generating VCC .... and it's a adjustable voltage regulator (bm1117).
But the Vin there is very low too.
Anyway there are no low-impedence paths on the Vin and Vout line .... but nearby there is this little component who looks very suspicious.
One pin is attached to bm1117 Vin the other one is attached to 12v line (present).

Since the Vin should be more or less in that range (20v max) and Vout should be in the range 3.3v-5.0v (GS7103 VCC) I think think the problem is that little component ...
it's a fuse or something else (it's not open and it's not short ....)

Are you able to identify it?

[saronno]

This is from a rx470 ... same thing, more or less ...
http://nekosoftpc.blogspot.com/2019/06/radeon-rx470-8g.html



I replace the "the little component" with  a 0 ohm resistor ... card is up and running.