Troubleshooting RGB Video Connection - Page 1
Forum section: electronics / beginners

author: Legion
author_rank: Frequent Contributor
timestamp: July 05, 2014, 05:03:09 pm
content: I've got a Sega Master System hooked up to a Micomsoft Framemeister to capture game footage. I'm getting audio but no picture. I've done some troubleshooting to narrow down the problem, but I'm getting conflicting results.It's connected like this:Sega Master System -> RGB SCART cable -> Euroscart to 8 pin mini-din adapter -> Framemeister -> TVThe TV is getting a signal from the framemeister which is just a blue screen with the words "No Input". This is what the framemeister ouputs when it does't get a signal. But audio is coming through fine.A couple times, for a brief moment (1 or 2 seconds) I got picture. But the image was distorted. The distortion looks like bad antenna reception.I checked the euroscart to mini-din adapter for continuity and that the correct pins are connected. Everything checks out. No shorts, and good continuity.I haven't checked the RGB SCART cable for continuity directly, but I've been using it with my monitor for a month now and picture/sound come through no problem. So I don't know how the cable could work with the monitor, but not the framemeister.Sega Master System RGB output over the RGB SCART cable works fine when connected directly to the monitor.I've tried the exact same setup except with an N64 and a Sega Genesis. Picture and sound come through fine.Suggestions?

author: Legion
author_rank: Frequent Contributor
timestamp: July 05, 2014, 06:49:57 pm
content: Apparently the problem is in the sync signal. The sync signal is pulled out of the composite video signal. On the framemeister there's a setting called Sync Level which is an integer that can be set between 0 and 31. Unfortunately there's no documentation for it so I don't know if it's a gain setting, or a threshold or something else. It defaults to a value of 9. I tried extreme values (0 and 31) but neither worked. After a lot of trial and error the best result came with a value of 16.I'm wondering if I can avoid messing around with this setting if I clean up the sync signal with a sync stripper inserted somewhere in the signal chain. Something small with a male BNC on one end and a female BNC on the other. The LM1881 seems to be the recommended IC from what I've read.

author: miguelvp
author_rank: Super Contributor
timestamp: July 05, 2014, 07:32:54 pm
content: Lot's of good info on this post:http://shmups.system11.org/viewtopic.php?p=754754#p754754Other than the LM1881 I've been looking at the EL1883http://www.intersil.com/en/products/audiovideo/video-ics/video-sync-separators/EL1883.htmlAnd other ones from Intersil and TI that might work at 240p.BTW I got the SDRAM working on the FPGA but I need to create a two line buffer because working directly with the SDRAM causes jagging, but I might get to that this weekend. Then to the SD card.

author: Legion
author_rank: Frequent Contributor
timestamp: July 05, 2014, 08:56:49 pm
content: Thanks for the info. I'll take a look at the 1883.RE: SDRAM, what do you mean by jagging? Like screen tearing?

author: miguelvp
author_rank: Super Contributor
timestamp: July 05, 2014, 09:06:45 pm
content: Quote from: Legion on July 05, 2014, 08:56:49 pmyeah, tearing, but that's because i'm bursting one 16bit word at a time, makes more sense to store one line in the FPGA and on the next line write that to the SDRAM while double buffering the 2nd line on the FPGA and double buffer between SDRAM banks.It will cause a delay of one line time to capture the screen but even if I was to display it it would be 1/(240*60) seconds, so negligible for all purposes (69.4444 microseconds)