- Nice little card, got it cheap, appears to have missing voltage rails
- Vcore – 0.4Ω
- VMem – 51.3Ω (bottom phase, nearest PCI, Samsung)
- PEX – 76.5Ω (U7)
- 1.8V – 863Ω (U852, L20)
- 5V – 475.8Ω
- 3.3V – ~32Ω
- 12V – ~1M (Slot), ~5KΩ (6pin EXT)
- VCore, VMem & PEX all missing
- 1.8V, 5V present
Investigating the missing power rails
I think VCore should be where to start. The U505 PWM is https://pdf1.alldatasheet.pl/datasheet-pdf/view/1222413/UPI/UP9511P.html
We have 5V and 1.8V, so let’s check a few things about our uP9511P
5 V on its VCC – yes
3 V on EN – No
VREF pin should be 2V – Not checked
Check why VCore EN is missing…
Moving to checking the source of NVVDD enable, there is a logic gate U506 that requires:
Output (pin 4) is very low, nearly 0V, this is EN for U505 above. VCC is there at 3.3V, so we need to check both inputs.
Input A (pin 1) – 0.562V Too low, this source is called PS1_NVVDD_EN_PROT and is comprise of several critical protection circuits e.g. thermal alert, over-current.
Input (pin 2) 1.8V – Correct, this is pgood from the 1.8V rail
The source of PS1_NVVDD_EN_PROT isn’t trivial, there are a number of components that can pull it low and it also requires NV3V3, which I have seen missing on a GTX 1080 TI. Although, with this board being mini, I am not sure the circuit is as complete as it can be with standard cards.
The things that influence this protection circuit are:
- Presence of NV3V3 (need to check if this exists on this card type)
- D507 – I cannot locate this, this card probably doesn’t have this circuit.
- D505 – I cannot locate this, this card probably doesn’t have this circuit.
- Q130 – This is definitely present, connects to U506 input A and is nearby.
(!) Discovered two missing components on the back of the card, Q521,Q522. Need to find out what these were, appear to have been switching components, at least the pads look okish.
(!) Discovered two missing capacitors in the same general area, the look like standard VRam capacitors. Need to replace them later.
I can see from the circuit and schematics here, that the missing transistors Q521 and Q522 are likely connected to the protection circuit and in turn, enable missing on the VCore PWM U505:
Replacing the missing transistors…
I am not sure exactly what Q521 and Q522 are, but they are likely some reasonably common p-type enhancement mode MOSFETs (like IRLML6402). I have a donor gtx 1060, I found Q522 on it and took two of the same component to replace with:
Success! We have a picture! 🙂 Right, the card needs a good clean, but I want to test before fixing those two capacitors:
- Drivers load – nice
- Card seems stable under light load (GPU-Z render test) – Thermals seem to behave well.
- Kombuster HD – Seems really good, with stable FPS. Over time, the temperature mounts to about 75°C. This card seems like more of a desktop / light gaming model, very nice and compact though.
- Identify those missing VRAM capacitors, might be 1uF or 10uF or similar, then replace them
- Further testing.