Roland S550 sync issues w/ custom profile #470
Description
I've used this project for years and recently designed an internal card for a Roland S550 sampler, based on LinuxJedi's Amiga 2000 video card (with permission). I noticed that the signals for the external RGB port were routed to the internal expansion connector and so added it when I was cloning the original (and rare) SCSI card - with the caveat that there's no commercial card that used these signals previously.
I have everything 'working' - while the picture itself is really high quality, I'm plagued by intermittent screen blanks/flickering, which I understand is related to re-establishing genlock sync. I am using a custom profile based on a 14.36Mhz clock (from the service manual), and have also tried a 7.1818Mhz setting (as there's a divider prior to the TMS chip). Although none of the sampling adjustments appear to resolve the problem, turning the genlock speed to off or slow does seem to eliminate the resyncs (with the obvious caveats).
Given the V sync + H sync signals are delivered down a ~20cm piece of ribbon cable (used to connect the card), I'm suspecting that it might be electrical noise. I've probed with my scope and do indeed see that the signal is quite noisy, but I'm also unfamiliar with what would be expected (plus the fact that these signals would be potentially delivered over feet of wire in more analog times). I did wonder about hacking an RC filter onto the board, but I'd like to try to understand the problem better first.
Can I ask for some help in a.) determining if there are more configuration options I could try, or how I might otherwise attempt to debug the issue? Thanks in advance!