Atari Analog Vector Graphics
Playing Blind
We encountered several Atari vector classics that “work” but don’t “show” in that the game plays and sound works and controls control but the game is not visible on the monitor.
A Suggested Fix
There is an AVG (Analog Vector Generator) in these machines that converts the digital line segments(vectors) into an analog signal the monitor chassis can produce. Part of that circuit is 4 chip labelled T085 (or SG085 or something 085). They are located in the video section of the board. In my experience with Space Duel they are at locations A10, D10 and D/E11 and D/E12.
Testing with a logic probe indicates there should be signal on pins 1 and 7 of A10 and D10. D/E11 and D/E12 should have signal on pins, 1, 2, 3 and 7.
Diagramming
A10 and D10
| Low | Low | Low | Signal (L/H) |
| 4 | 3 | 2 | 1 |
|---|---|---|---|
| Notch | |||
| 5 | 6 | 7 | 8 |
| Low | Low | Signal (L/H) | High |
D/E11 and D/E12
| Low | Signal (L/H) | Signal (L/H) | Signal (L/H) |
| 4 | 3 | 2 | 1 |
|---|---|---|---|
| Notch | |||
| 5 | 6 | 7 | 8 |
| High | High | Signal (L/H) | High |