Automatic Repair on Boot Keeps Happening

I have a desktop PC using a Gigabyte GA-Z77X-UDH mother board c. 2012 with the latest BIOS and running Windows 10 v1809. I turn the PC off at the mains when not in use

I've had a few occurrences during the past 3 years when the PC fails to boot on initial power on and goes into automatic repair. The PC then boots normally if I switch it off at the mains then switch on again and start. Running chkdsk never finds any problems. See the old thread Automatic Repair Started on Boot?

I've discovered this doesn't happen provided after turning on the mains switch, I wait around 10 seconds before turning on the PC with the power on button. Is this likely to be an issue with the PSU or motherboard?

Because of capacitors on the mb they will still have power for a short while after power off its normal

Samuria said:

Because of capacitors on the mb they will still have power for a short while after power off its normal

I don't understand that. The PC has been left overnight turned off at the mains. Surely in this condition the capacitors will have discharged. On switching on the mains, the PSU is in standby and sends a +5V standby power line to the motherboard. There may be short delay for that standby line to stabilise and charge certain components before the motherboard will power on normally. I suspect that's the problem I've having.

The problem occurring a few times in three years makes it hard to modify and test.

When there is an automatic repair these are some options:
a) search for srttrail.txt > it may or may not display a cause
b) turn off automatic repair using command line > see if it produces an error message or code

zbook said:

The problem occurring a few times in three years makes it hard to modify and test.

When there is an automatic repair these are some options:
a) search for srttrail.txt > it may or may not display a cause
b) turn off automatic repair using command line > see if it produces an error message or code

I don't have the file srttrail.txt. I disabled automatic repair so will report if I see an error code.