Cmherndon79 Posted May 22, 2020 Share Posted May 22, 2020 Hi there, Got an NTSC 7800 in from someone that wanted it modded for composite video and audio output. Board is CO25233-002 Rev A. This is just the simple and cheap mod using the 2.2K, 3.3K resistors and the 2N3904 transistor, mounted on a PCB. Done many of these on 2600s (maybe 150+ by now) and probably 10 7800s before. When I got the unit in, I just booted up Frogger in 2600 mode over RF channel 3 and sound and video were working fine. Foolishly I didn't check to see that the MARIA chip in 7800 mode was working before I did anything further. I took the board out and replaced the 3 electrolytic capacitors from a kit from Console5 that I had on hand and replaced the audio polystyrene caps at C4 and C5 with so 820pF MLCC equivalents. I removed the RF modulator from the board and I installed the composite mod. I booted Frogger back up and the screen looked normal, colors were correct. TIA audio was playing fine on the startup sound in Frogger. Next, I put in Ballblazer since that had a POKEY chip in it, it is typically the first one I'll use. When it switched into using the MARIA for the 7800 I got almost all black and white in the Atari rainbow, except for yellow. When I watch Ballblazer in attract mode I see all black and white, but after the ball is hit, I see it turn yellow and after a second grey again. No problems with POKEY audio. Put in Food Fight and Centipede (7800) and same behavior. Started looking for problems on the board. Noticed the rear leg of C57 was sitting in the mounting hole for the power connector, seemed unlikely this was the problem, but I connected it to where it was supposed to go and no change. Checked all the component connections around MARIA and didn't find any problems, but did reflow a few things that looked like they could be marginal. Checked for bad solder joints everywhere else and same thing, nothing apparent but reflowed a few points anywhere I thought things could be marginal. Double checked the polarity of the electrolytics I installed and they were right. Reflowed the solder on the 220uF cap sitting next to the MARIA just in case. Did a search and found someone had B/W only here on a 7800, which was a bad solder connection at the slot, so I checked that, but didn't find anything wrong there. Can't see any cut traces and checked continuity if I wasn't sure. Just looking to see if anyone else has run into behavior that fits this description. I've got a known working MARIA in a socket on another 7800, but I really don't want to desolder the one from this board, unless I'm fairly confident that is the problem. Thanks! 1 Quote Link to comment Share on other sites More sharing options...
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