Seller Note “The graphics card is DEAD unresponsive. NOT powering up.”
Summary
- I bought this as I have another similar card with a short that I wanted to get some measurements for Gigabyte RX 460 2Gb. It appears to have the same fault, hopefully, it can still help.
- Resistances
- Vcore – 2Ω
- VMem – 58.2Ω
- VDCCI – 37.8Ω
- Display Rail – 32.9Ω
- 1.8V – 2.01KΩ
- 5V – 3.78KΩ
- 3.3V – 3.3KΩ
- 12V – measures about 1KΩ (slot), but this is false since the 12V fuse is blown. I would expect the true resistance to be higher
Investigating shorts on 12V rail
OK, if that 12V rail fuse is blown, let’s start there and measure the VCore high-side MOSFET gate resistances. Here we go, the top one Q512 has a low gate resistance of 5.6Ω, whereas the other three phase’s gates measure ~8KΩ. Let’s remove that MOSFET and see what happens to the 12V rail resistance.
After the removal of Q512 and a new 10A fuse (F3), the 12V rail read a healthier 4.5KΩ. Testing with power, we have a BIOS picture, so the core hopefully isn’t completely dead!
What I don’t know yet is if the driver is also bad, replacing the MOSFET can sometimes end in disappointing smoke if there is an underlying issue. I will test the gate to see if there is a decent-looking waveform with an oscilloscope. Waveforms all look reasonable across all 4 phases.
I need to buy some K03B7 high-side MOSFETs, unless I can find a donor card.
Update – Working and needs more testing
After replacing the faulty MOSFET, the card seems to be working and all 4 phases are showing the same waveform on an oscilloscope, so hopefully, it’s in good shape! 🙂
Next steps
- These little RX 460s are really just desktop cards, not designed for any real kind of gaming.
- I noticed that the fans cut in quite late and whilst the core remains at a low temperature under full load, the VRM area at the back of the card feels hot.
- Will continue to test and maybe take a look with a thermal camera to make sure no components appear strangely hot.
- There may be space to fit a stick-on heatsink to the VRM MOSFETs. Having worked on two identical cards each with a blown MOSFET, I am guessing the VRM area is a weakness on this model and a bit of extra heat dissipation might help.