I have been troubled by my 5V Arduino Nano's with MEGA328P processor not always booting.
The Nano's are powered by a separate 5v supply. This is necessary for the load. I only plug in a usb lead to download a new sketch.
With this setup, I have the fuse removed to make sure the usb connection never powers the board.
It works well but sometimes the board will not start (sketch not run).
Having used Pro Minis and Megas, which always start, I was very suspicious of the CH340G chip.
Searching the web suggested it may be a problem.
I have tried various fixes.
Local power capacitor fitted for smoothing and noise.
Different bootloaders
Linking TX and RX
Grounds/resistors on TX and/or RX.
Nothing seemed to completely solve the problem.
Hence time for drastic measures. I cut the track to the CH340G power pin 16 and linked it to the usb connector power pin.
This change results in the CH340G chip being powered only when I plug in the usb lead.
Now my sketch runs on every power up and if I plug in the usb lead I can reprogram the Nano.
Not a solution I was looking for but I needed a fix and I am happy with this.
If you have had problems with boards with the CH340G chip and booting problems, I am interested in your solution.
Comments please