CRT is good, using on another comp.Is the CRT good - have you tried a nubus video card on it? The 840AV has 1MB soldered VRAM I’d pull whatever is in the 4 X VRAM slots as first troubleshooting step.
Yes, I agree it maybe wasn’t a good comparison to make. Bad VRAM usually manifests as artifacts or other visual glitches but not digital snow.I'm not so sure it is VRAM. Like others have said, it isn't putting up bad data, it's... All over the place. It's more likely a bad trace or dry contact in the video circuit.
@croissantking no VRAM at all is a very extreme case to compare it with, given the chips are physically there, isn't it more likely an issue in the video circuit that impacts more broadly, than a VRAM specific fault that breaks all the VRAM (that's a lot of chips and traces to fail)?
Could it be a bad chip, in that case? Your logic board looks clean.I have Looked over nearly every single trace, checked connections beteende ic legs and board. I cant find anything weird.