Seller Note “When installed in pc the fan spins but with no output to the screen unfortunately otherwise in great condition”
Pre Checks / Multimeter Only
| Test / Checks | Result | Notes |
|---|---|---|
| 1. Visual Inspection Eye / Magnifying Glass | OK | No missing components, but a bit dirty. |
| 2. Visual Inspection Microscope | – | |
| 3. Check for shorts on 12v PCI, 12v PCI-E, 3.3v | OK | Couldn’t find any obvious shorts. |
| 4a. Resistance VCore (~0.5) | Ω | |
| 4b. Resistance VMem (~60Ω) | Ω | |
| 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 | |
| 4g. Resistance 8.8v Rail (18.7KΩ ) | KΩ |
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 display (no light on monitor) Fan spins, GPU never gets warm (no power). Some warmth in the VRM area. | No power to CPU. |
| 2. Voltage VCore (~0.88v) | 0.914v | OK |
| 3. Voltage VMem (~1.4v) | ~0v (4.3mV) | !!! Need to investigate further |
| 4. Voltage PEX Rail (~1v) | ? | !!! |
| 5. Voltage 3.3 BUS | 3.3v | present |
| 6. Voltage 12 Ext | 12v | present |
| 6. Voltage 5v Rail | 5v | present |
| 7. Voltage 8.8v Rail | – | – |
That memory area needs further investigation, access is a bit hard with the cooler in place. The board is quite small and the heatsink is quite large and gets in the way of diagnostics. I will see if it can be run with a make shift heat sink. Alternatively, I will try and rig up a lab power supply to a riser.
Next Steps
Actually there is no need for a heatsink, as the GPU remains cold. There is some warmth towards the IO shield / VRM area, but hard to pin point. Still cannot find any trace of the 1v PEX rail. I am guessing VMem is missing perhaps because PEX is also missing. Hopefully there is a chance that the core and memory are ok and there is some failed power switching/delivery component. Interesting!
Deep Dive
Used my cheaper microscope to take a closer look at the PCB, in particular components relating to possible minor voltage production (VMem 1.5v, PEX 1v). Found two Low Dropout Regulars to investigate (refer to Fig 1 & 2 in photo above for positions) :
I struggled to find a datasheet for these exact components, but I did find this seemingly very helpful image from a Russion site:
Also here is a link for a similar chip http://images.100y.com.tw/pdf_file/38-RISHTEK-RT9018.pdf
Time to check voltages on these chips:
| PIN | Expected V | Actual V |
|---|---|---|
| 1. PGOOD (Dot) | From vCore? | 0v Missing |
| 2. EN | 2v+ ? | 3.07v OK? |
| 3. VIN | 3.3v | 0v Missing |
| 4. VDD | 5v | 5v OK |
| 6. VOUT | 1v | 0v Missing |
| PIN | Expected V | Actual V |
|---|---|---|
| 1. PGOOD (Dot) | From vCore? | 0v |
| 2. EN | 2v+ ? | 5v OK? |
| 3. VIN | 3.3v | 0v Missing |
| 4. VDD | 5v | 5v OK |
| 6. VOUT | 1v | 0v Missing |
Seems we could have a problem with the 3.3v rail.
TODO Test resistor R649
Want to understand more about the Vmem rail.
RT8120A http://www.chipset-ic.com/datasheet/RT8120A.pdf (single-phase synchronous buck PWM DC/DC controller designed to drive two N-MOSFET) I am guessing this drives the two MOSFETs in the memory VRM.
Also there is a chip marked 0T=1C 622 which I think is a PWM used to drive the Vcore VRM http://www.smdcode.net/uploads/Files/Datasheet/0T/RT8811A.pdf
Update: Unfortunately, I accidentally shorted to of the Vcore mosfet pins whilst measuring with my new meeter, smoke seen and now no VCore – dam it! The driver appears to have a burn mark on it, would imagine at least the driver and the mosfet need replacing. This is now long fix territory, as I need to find replacements and hope for the best in terms of no further collateral damage.