This guide will cover how to identify and read debug codes provided on some motherboards. Please note, not all motherboards will include these debug features. For further information, please check your motherboard user's manual.
A useful feature found on many motherboards are debug features that can help a user easily identify and resolve hardware issues with minimal guess work.
For motherboards with debug features, two of the most common types you'll find are either a set of Debug or POST LEDs (also known as Easy Debug LEDs, shown left) or a 2-digit, seven-segment Digital Debug LED (also known as a Q-Code or Dr. Debug, shown right).
Some older PCs may also include a small speaker or buzzer that sounds off when the PC starts, while some more enthusiast centric motherboards may include more complex OLED based displays that can read out the exact error code. For this guide, we'll be focusing on the more common POST LEDs and POST Code Display.
What is POST?
POST stands for Power-on Self Test, this is an automated process that happens every time your PC starts where the PC will test the installed hardware to confirm everything is properly detected and running. If a PC fails to complete POST, it will not be able to boot into the operating system.
Reading POST LEDs
POST LEDs are usually going to be a group of four LEDs labeled CPU, DRAM, VGA, and Boot as shown in the image above. Depending on the motherboard, these lights may be color coded or arranged differently so it is always recommended to check the motherboard user's manual. The above example is taken from an NZXT N Series motherboard and is located on the bottom edge of the board near the Power and Reset buttons.
When the PC starts, these LEDs will light up and turn off in sequence based on the POST, starting with the CPU and followed by DRAM, VGA, and finally BOOT before going completely dark. In the event that a POST fails, the system will do one of three things:
- One or more LEDs will light up and stay lit indefinitely until the PC is shut down.
- The LEDs will bounce between two LEDs indefinitely.
- The sequence will stop after an LED turns off, but will not continue to the next step.
For any of these situations, the last/furthest LED is likely going to be the cause for the issue.
CPU Debug LED
Generally the first LED in the sequence that indicates the CPU is being checked. A stuck CPU LED means that an issue was found with the CPU which can include, but is not limited to:
- A loose or disconnected 12V CPU Power Cable
- The CPU is not properly installed
- The CPU is not compatible with the motherboard
- The CPU is faulty and needs to be replaced.
DRAM Debug LED
The second LED in sequence that indicates the RAM is being checked. A stuck DRAM LED means that an issue was found with the RAM which can include, but is not limited to:
- No RAM is installed or detected by the PC
- One or more RAM modules are loose
- One or more RAM modules are not compatible
- One or more RAM modules are faulty and needs to be replaced
- The RAM controller on the CPU has failed, requiring the CPU to be replaced
VGA Debug LED
The third LED in sequence that indicates the GPU or iGPU (for systems without a dedicated, discrete GPU) is being checked. A stuck VGA LED indicates that an issue was found with the GPU which can include, but is not limited to:
- No Monitor Detected (Invalid source or Disconnected)
- No GPU Detected
- The GPU has reported a hardware error and is hung
- The GPU does not have sufficient power
Boot Debug LED
Generally the last LED in sequence, indicating that the PC has completed testing all prior hardware and is attempting to load either into the UEFI Settings or the Operating System. A hanging Boot LED is fairly uncommon, but will indicate that an issue was found that is preventing the PC from loading into the UEFI or Operating System. This can be caused by, but is not limited to:
- No storage detected
- No valid Operating System detected
- Invalid boot settings
Reading a 2-digit POST Display
Depending on the motherboard, you may have a 2-digit, seven segment display that cycles through codes either as a replacement or in addition to a set of POST LEDs. These displays are greatly preferred by a number of enthusiast builders as they are able to provide more detailed information than POST LEDs when it comes to debugging a PC. Like with POST LEDs, if a code hangs then this is should point you to the exact source of the issue. For an accurate breakdown of what these codes mean, please refer to your motherboard user's manual or the product page on the manufacturer's website.
Common codes however include the following:
- 00 - 3F codes - Pre-Boot or CPU Issue (Motherboard or CPU Issue)
- 40-5F codes - Memory Detection and Initialization (RAM Issue)
- 90-9F codes - Display Detection and Initialization (GPU Issue)
Codes such as FF or A2/A0 indicate that a motherboard has completed POST and is preparing to boot either into the UEFI Settings or into the Operating System. It is worth noting however that once a PC completes POST, this readout may either turn off or may switch into Temperature Mode depending on the motherboard. For more information, please refer to the motherboard user's manual.
How do I fix a POST issue?
Once you've identified the POST issue, we can now work to isolate the problem. Depending on the LED you see, please check out the guides linked below:
- NZXT Support - Identifying CPU Issues
- NZXT Support - Identifying RAM Issues
- NZXT Support - Troubleshooting GPU Issues
- NZXT Support - Identifying BOOT Issues
Do you have any questions not covered by this guide or need further assistance? Please feel free to reach out to our Customer Support team and one of our friendly support agents will be there to assist you.
Are you looking to keep up on all things NZXT? Go ahead and join the Official NZXT Community Discord to keep up to date on our latest products, upcoming sales, and join in on discussions on everything from PC hardware to gaming.
You can also follow us at the following links:
Comments
0 comments
Article is closed for comments.