In what I hope could be a useful resource to people using the CPU-less flashing features on motherboards, I just wanted to share my experience on using Gigabyte's QFlash Plus on a B550 board.
The process is not clearly documented, seems to vary between manufacturers and perhaps even boards, and often needs a very specific process to be followed TO THE LETTER.
After struggling to get the feature to work on a Gigabyte B550 board and knowing a friend had similar trouble on an X570 board, I encourage forum members to share their own experiences including resolutions. Depending on how many replies we get, I'll aim to link to individual posts from the OP or the reserved post below. Or if there are other threads/posts detailing the process, I could link to those too.
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So for some background, I started with a Gigabyte B550 board and a R5 5600G CPU. Knowing this CPU would likely not be supported out of the box with stocked B550 boards, I specifically chose one with a CPU-less BIOS update feature after checking a compatible BIOS was available.
Long story short, I installed memory and CPU just to try booting first, on the off-chance it would have an updated BIOS or at least allow me to flash the new BIOS the conventional way. Nothing. The board powered up but no output. Even the power button did not work to switch off the system.
So I tried using the QFlash plus feature. As it happens I had already found online that the BIOS file must be renamed GIGABYTE.BIN in the root of a FAT32 formatted drive. I plugged this into the allocated white USB port and pressed the QFlash button. Nothing. Tried holding it down, nothing. Tried doing it after powering on the computer, nothing. This process of randomly trying button mashing and power cycling went on for a while thinking it might just be temperamental, but nothing seemed to work. I tried another flash drive, tried leaving the BIOS file name unchanged, reformatting the drive etc as various anecdotes online claimed success after similar methods, but nope, nothing helped.
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Fast-forward to the solution.
Eventually I removed the memory and CPU and cooler and followed the same process. BIOS file renamed to GIGABYTE.BIN, in the white USB port, then pressed the button. Nothing. I knew a friend had used the feature but on an MSI board I believe. He suggested holding the button down again. FINALLY!
I would suggest using a USB drive with an activity indicator LED so you can see when it's being read. Also leave your case open or do this outside of a case so you can observe the flashing QFlash activity LED. No idea whether it matters but I used an 8GB FAT32 formatted drive with default allocation size, some claim they've been unsuccessful with larger drives then successful with a smaller one. It's hard to know if that's the real reason but it's worth bearing in mind.
Once the flashing starts, leave it alone. After a while (5-10 mins roughly) I heard the system power up via an optical drive connected to the PSU and saw the PSU fan spinning. Again I just left everything alone until it switched itself off again, then a while longer just to be sure. Then I reinstalled CPU/memory and thankfully, it booted fine.
Also, I made sure to unplug all drives from power (to avoid constantly power cycling them with unexpected power loss), and unplugged all SATA cables just in case. I had the 24 pin and 8 pin CPU power connected. The CPU power is possibly unnecessary but having it connected didn't cause any problems for me.
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From what I could find, this process including the specific requirements such as HOLDING the button, having CPU/RAM REMOVED, and RENAMING the file are not mentioned anywhere in documentation which is quite poor. The manufacturers could really do a better job of explaining this process. One version of the motherboard manual I found didn't even mention the feature besides labelling the port/button/LED in the diagram. Another version did mention the process and suggested it can be performed without CPU/RAM installed but did not say this was mandatory. I had avoided removing the CPU as it was awkward in the case I was using and meant disturbing the pre-applied thermal compound.
This is further complicated by the various anecdotes online - for some people, it has worked fine on their boards with CPU/RAM installed, but it seems it can vary greatly even for boards from the same manufacturer.
So there you have it. An evening of frustration typed up in the hopes others can avoid it.