exxos's Atari, Amiga & retro forum

I also suggest you try with the full metal shielding in place and clamped down properly with the tabs twisted.

So far I have tested the bare board, no plastic case, no keyboard or mouse, just the board, power and RGB.

Tested the following:
1. Diode to pin 40 - Voltage dropped to 4.4v but same issue
2. PSU recapping - Same issue

I'll look to connect the RGB wires directly to the monitor (Need to somehow take everything other than RGB lines from the monitor out...) and now also try with the metal lid on, although as I'm testing just the board, not sure how much it will make a difference.

Your getting interference from somewhere. It doesn't make sense how you got worse results with a DAC. The only change I can think of is your monitor cable is picking up RF from the motherboard which wasn't happening before.