I picked up an Atari Tetris the other day that's part of a little side project I have going (at some point I'll make a thread on that) and I drove over to a friends house to install it. Unfortunately after getting the JAMMA harness fixed up and installed I couldn't get the video working. Like nothing, zip, nada. The board was tested (and test results forwarded to me) before I bought it and it was shipped well (in anti-static bag too) so I wasn't expecting issues. Fortunately I threw a scope in the truck before braving the snowstorm to get there. I poked around the board and it all looked good. I was even getting video signals that looked OK, at least from a cursory point of view anyhow. Since I had limited time and I didn't have a 2nd board or monitor on site I packed everything (including his monitor) up and dragged it all back home to work on it here. I took the game downstairs and hooked it up to my test bed and a known good monitor. I got a scrambled image but it was recognizable so I it would seem the board works and it's a monitor issue. However, I spent probably 30 minutes trying to get the dam thing to sync to no avail. At this point it was time to break out the Oscope again and take a look at the video signals. They are attached.
One thing to note is that Atari Tetris is JAMMA (negative composite) but also has a secondary video header for Positive sync monitors. So I started pulling waveforms from there as it was easier than the edge connector.
The 1st is Positive H sync, 2nd is Positive V sync, 3rd is Red (blue/green are similar). These signals all look good. Note all are at 1v per division, but I changed the period for each.
One thing to note is that Atari Tetris is JAMMA (negative composite) but also has a secondary video header for Positive sync monitors. So I started pulling waveforms from there as it was easier than the edge connector.
The 1st is Positive H sync, 2nd is Positive V sync, 3rd is Red (blue/green are similar). These signals all look good. Note all are at 1v per division, but I changed the period for each.
