Gigabyte RX 460 2Gb

Seller Note “No display output on start up.”

Gigabyte RX 460 2Gb

Summary

  • Nice, clean condition, nice neat little card!
  • Resistances seem OK (2.4 Vcore, 36.6Ω Vmem – seems a little low)
  • Completely dead, no fan spin, no voltages anywhere obvious.. blown fuse
  • Can see a fuse, will invetigate deeper into power rails.
  • There is a boadview / schematic for this card, which is very helpful.

Pre Checks / Multimeter Only

Test / ChecksResultNotes
1. Visual Inspection Eye / Magnifying GlassOKVery clean, nice board to look at.
2. Visual Inspection Microscope
3. Check for shorts on 12v PCI, 12v PCI-E, 3.3v12v Short!There is a blown fuse on the 12v rail. There is a short behind it.
4a. Resistance VCore (~0.5)
4b. Resistance VMem (~60Ω)36.6Ω
4c. Resistance 3.3v Rail (~960Ω+) Ω
4d. Resistance 5v Rail (~5KΩ)K Ω
4e. Resistance 1v PEX Rail (~123Ω+)Ω
4f. Resistance 12v BUS (14.7kΩ )

Other Resistance Checks

Measuring continuity to ground at the other end of the fuse (not the end near the PCI input) results in continuity, so there is probably a short somewhere that caused the fuse to blow.

Measuring from the isolated end (separated from 12v PCI power input) of the fuse:

  • To ground of 2Ω
  • To Vmem inductor is 36.6Ω -> Vmem VRM healthy.
  • To a Vcore inductor is 0Ω -> implies one or more Vcore MOSFETs are shorted.
RX 460 Blown Fuse – 12v Short

VRM Analysis

First, let’s check the gate resistance of each high-side MOSFET

High Side MosfetGate Resistance
Q514 (phase 4)8.00kΩ
Q509 (phase 3)2.8Ω !!
Q505 (phase 1)7.97kΩ
Q502 (phase 2)8.01kΩ

The gate resistance of Q509 (phase 3) is clearly abnormal.

As a second opinion, let’s also check the ESR of each phase

PhaseESR
1~1.20Ω
2~1.20Ω
3~1.09Ω
4~1.20Ω

Phase 3 has a lower ESR, implying this is the phase that is shorted.

Think the shorted high-side MOSFET is on phase 3 (Q509). Need to remove & test if the short is resolved.

I removed the MOSFET from phase 3 and the resistance on the 12v rail is now normal (no short).

RX 460 Removed Faulty MOSFET

With that, I want to check if I can now run the card, albeit in a compromised state. Unfortunately, my order of fuses hasn’t arrived yet, so I need to bridge the blown fuse for now with a small piece of wire:

RX 460 Temporarily Bridge Blown Fuse

Excellent! The card now powers up and can access windows. However, the remaining VRM phases seem to be working very hard and the low-side MOSFET on phase 3 is very hot! In GPU-Z VRM efficiency is very unstable and jumps around 39%. Next, I need to order a replacement high-side MOSFET and possibly a driver just in case.

High-side MOSFET Q509 is AON6414AL

Driver U506 is NCP81161 https://www.digikey.co.uk/htmldatasheets/production/1129670/0/0/1/ncp81161.html

Power On / Test Rig Checks

Tests / ChecksResultNotes
1. Observations (e.g. PCB heat noticed,
blank screen, power light on monitor,
bios screen, o/s loaded, artefacts, )
No power at all, fuse blown.
2. Voltage VCore (~0.88v)
3. Voltage VMem (~1.4v)
4. Voltage PEX Rail (~1v)
5. Voltage 3.3 BUS
6. Voltage 12 Ext
6. Voltage 5v Rail
7. Voltage 8.8v Rail

Extra Info