BIOS Problems on Pascal GPUs

Symptoms of having a problem with the BIOS.

• All voltages (5, 1.8, vcore, vmem, and PEX) are present on the card but no output or backlight even after sometime (if there is backlight the problem is the memory).
• The card does not get recognized by MATS.
• The card works but unreliably (sometimes works but after power cycling it doesn't work)

The BIOS circuit.

(Figure 1) Location of the BIOS chip on the board (U3).

(Figure 2) Schematic view of the BIOS circuit.

Different board manufacturers might use different bios chips, however, they have have the same pinout and work in the same principle.

Markings on the schematic and board could differ from GPU model to another but the circuit is almost always the same.

Here is a reference datasheet.

The resistors for pins 1, 2, 5, and 6 are sometimes on the back of the card close to the core.

Usage.

During initialization, the GPU core pulls pin 1 (CS) low which enables the bios then proceeds to reads the information stored on it, such as the name, clocks, etc.. of the card by communicating through pin 2 (directly connected to the core) and pin 5 (goes through a 33Ω resistor) as shown in figure 2 . After that those readings are then sent to the computer.

Identifying Problems.

First, make sure the bios chip is receiving power through VDD pin.

Then, with an oscilloscope, probing pin 2 and 5 during initialization tells you whether the core is communicating with the bios or not in the first place, if there is complete silence that means the core is not even trying to talk to the bios(probably faulty core or the card has not reached the initialization point). If there is communication then it's either the bios chip is faulty or the BIOS data either got corrupted somehow or a modded/incompatible bios has been flashed on it. Simply flash the original bios (from TPU BIOS Library or the manufacturer's website) using a SPI/USB adapter. Or If there is no communication then check the resistors between the bios and core.

At this point, if the bios is being read and the bios chip is working and has original content on it but still no picture then you probably have another problem, most likely a dead core.