Joust – WORKS!
Yes you read it correctly, Joust finally works. Yahoo!
So after endless hours fighting the monitor, I finally took a break and came back with a fresh approach. Turns out the monitor was working great, it just wasn’t being fed the V sync signal.
The schematics show the V-Sync and H-Sync signal coming from chip A4 on the CPU PBA (A TTL 7486N chip). So, I took my radio shack TTL tester and probed output of the H-Sync (pin #11) and got a series of beeps, typical…then, I probed pin #8 the V-Sync output and nothing but the low light and no beeps (no signal).. Ah HA! Next, I checked the input signal for the V-Sync on the same chip (pin #10) and again got the beeping. So, that part of the chip was being fed the signal, it was just stuck in the low state.
So I unsoldered the old chip, soldered in a socket and plugged in a new 74SL86 (see pic below).
Bingo Bango Bongo, the image FINALLY locks into place
