Seller Note “No display output on start up.”
- 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 / Checks||Result||Notes|
|1. Visual Inspection Eye / Magnifying Glass||OK||Very clean, nice board to look at.|
|2. Visual Inspection Microscope||–|
|3. Check for shorts on 12v PCI, 12v PCI-E, 3.3v||12v Short!||There is a blown fuse on the 12v rail. There is a short behind it.|
|4a. Resistance VCore (~0.5)||2Ω|
|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 )||KΩ|
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.
First, let’s check the gate resistance of each high-side MOSFET
|High Side Mosfet||Gate 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
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).
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:
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 / Checks||Result||Notes|
|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||–||–|