So currently I haven’t removed my motherboard or anything, so I assume that the atx power is how my computer is currently connected. But how would I turn my motherboard off then if power is still coming through? Or you mean like just don’t turn on my computer but keep power coming in?
I have a hardware programmer (SP8-F) that has 2 configurations for programming in-circuit :
a. Programmer supplies current to the target board
b. Current self-supplied by target board
For in-circuit programming the ch341a needs to supply enough current to power the EEPROM while it is connected to the motherboard, which is sometimes a problem as the current can drop when a SOP-8 clip is used and the motherboard circuit is still connected:
Attach the ATX PSU to the motherboard (with the BIOS chip) BUT DO NOT power on the motherboard via the case power switch (but only at the Mains supply). On my motherboard there’s board power switch with an LED which lights up to indicate ATX PSU is ready.
I was then able to read back, erase, write and verify the Main BIOS chip with my BIOS and the also the Backup BIOS chip with Gigabyte’s stock BIOS.
A note on the external supply: even though it is rated over 1A @ 3.3v, it does not regulate well. When not loaded, it supplies 3.26v. The voltage drops to around 2.86v when the Clip cable is connected to the motherboard BIOS chip. That voltage is within the tolerance of the BIOS chip. I measured the current drawn from the 5v USB supply it was drawing around 380mA during read/write.
The ch341a is the cheapest programmer with no circuit protection, there is no guarantee that it can program in-circuit and you may need to de-solder the BIOS EEPROM if it fails to read/write.