HDMI back powering problem

The "HDMI back powering problem" is the root of all evil!

The evil things that can happen range from display problems over SD card problems to issues around the system's overall stability.

The HDMI back powering problem is a bug in the MEGA65's hardware and happens on these board revisions: R3 and R3A.

If your MEGA65 is connected to any HDMI device: Never switch-on this device before you have successfully switched-on your MEGA65. Or to put it the other way round: Always switch-on your MEGA65 first and THEN switch-on your HDMI device (monitor, frame grabber, etc.).

While your MEGA65 and your HDMI device are switched off: Hold the No Scroll key while you switch on the MEGA65 and while the HDMI device is still off. Now, you can switch on your HDMI device and use the MEGA65's core selection menu to select the MiSTer2MEGA65 core. You can also use the key combination No Scroll + to directly select the MiSTer2MEGA65 core.

Another way to resolve the issue is to put a cheap HDMI switch between the MEGA65 and your device. You will find two Amazon links to devices that are known to work here in Dan's MEGA65 Welcome Guide.