I've got an 800XL that produces vertical bars that I've been trying to get rid of. Currently, I'm using SVideo (Chroma/Luma) -> VGA Converter -> LCD Monitor.
Initially I added the missing chroma line and lifted a single cap so that chroma was output on the 5-pin din.
I've removed the RF modulator
Installed a UAV rev D
I thought it might be some kind of cross talk/interference in the cable itself - the cable is one I hacked together using an AT KB Extension + SVideo cable. To eliminate the cable as the issue, I wired in a second 5 pin din (the female side of the AT KB extension) directly to the UAV and the result was no bars - clean solid blue background. I've checked the cable for continuity or even some level of resistance between between the pins on the cable and didn't get anything so I don't think its the cable.
The problem only happens when I try to use the built in 5pin din port. If I go directly from the UAV, everything is fine but when wiring the UAV output back into the motherboard, the problem reappears. I've narrowed it down to be something with the composite line. If I don't connect that line from the UAV to the motherboard (UAV Pin 2 -> L7), then everything looks fine. (The attached pic shows the ground wire hanging - that was part of testing; connected vs not connected didn't change anything).
Is there some kind of back-feed happening from the composite line onto the Chroma/Luma lines on the motherboard? Is that possible? I've removed the original Chroma wire (used pre UAV) - no effect. I put the 1 lifted cap back into the circuit - also no effect; i've since lifted it again.
Any ideas? Any other components that can be removed that will separate the composite line from the C/L lines on the motherboard?
Edited by TroyQ, Tue Jan 2, 2018 12:44 AM.