Seller Note “Dead”
- Vcore 4.6 Ohms
- Vmem 207 Ohms
- PEX 1.4 K Ohms
- 1.8v 5 K Ohms
- vcore 0.81v
- vmem 1.5v
- pex 1.0v
- 1.8v present
- OK, so given that all voltages and resistances appear in order, I went looking for reasons why the GPU might not wake up (assuming it is healthy). It seems this card to also has pcb damage like my other one, but in different places. Basically the PEX reset sginal AND gate and associated capaitor are missing (see pictures). I actually should have some spares I ordered for another card that has similar damage. Unfortanately it also looks like they ripped a pad.
The missing chip will be something like 74LVC1G08 https://www.farnell.com/datasheets/1645571.pdf
The pins will be like
|Pin||Name||Expected Voltage (taken from card A)|
|1||B (the damaged pad)||1.8v|
|2||A (the reset signal)||3.3v|
|4||Y (output to enable GPU to leave reset)||1.8v|
On this card (card B):
- pin 5 has 1.8v, but no smoothing capacitor
- pin 1 is dead, as expected due to a missing pad.
- pin 2 has 3.3v as it should.
- pin3 is fine
Problem 1 – Repair To PEX Reset Logic Chip
First I cleaned up the area and scratched away the solder mask on the source of the 1.8v using a craft knife.
First I tried using the pad type shown below, but it was a bit small and I couldn’t seem to solder it to the exposed 1.8v source.
Next, I tried a longer pad with a trace attached to give me more to connect to the 1.8v source. I managed to get a good solder connection despite the poor alignment and slight solder bridge to the other 1.8v pad. I chose to leave the solder bridge, as the pads are actually connected by the 1.8v circuit (obviously sloppy looking, but seems quite strong).
Finally, I managed to solder a new logic gate chip on. Again, I really need to work on my soldering! I will clean this up when I replace that missing capacitor.
However rough my work has been, the great news is that the board now works!
Problem 2 – Damaged Capacitor
I need to test this capacitor.