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Pre-show testing showed no issues and the game was submitted into the show. However, the monitor died a few minutes after power on. I tried swapping daughter boards with Galaxia but even a complete swap of all of them didn't bring the monitor back to life. It was withdrawn into the backroom before the show opened.
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I took a look at the MTC-90 chassis and found most of the power supplies missing, consistent with no secondary outputs from the first stage of the LOPT. It looked like the 200V supply was missing. By this time I'd had enough of the MTC-90 chassis having been unable to keep them working reliably for long periods or provide anything more than poor picture quality. Despite a significant investment already made in spare parts I decided that it was time to retire all three (Astro Wars, Galaxia, Sea Scare) of my MTC-90 chassis at their next failure :(
The project to replace the MTC-90 chassis with a later MTC-900 chassis, preserving the
original wiring, CRT & frame unhacked, is documented on its own page:-
Hantarex MTC-90 to MTC-900 Conversion
With the replacement complete it was time to begin long term testing with the 'new' MTC-900
chassis.
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After a few hours of burn-in testing there was no picture. Neck glow looked OK and HV was still present. I've seen this symptom before so I started inspecting the blanking signal at IC3 pin 2 (TDA1470), comparing against waveform 6 in the Hantarex manual. The signal looked OK, consistent with the manual. Following through R39 (150R) on the DS PCB onto the IS PCB through R28 (22K) and R27 (22K) showed the signal was OK at the base of TR8 (BC237). However, the output of TR8 to IC1 pin 10 (TDA3501/20620200) looked bad when compared to waveform 7 in the manual. Replacing TR8 (BC237) brought the picture back and fixed the chassis.
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After a few days of burn-in testing the picture began to periodically & briefly loose sync. I left the game running in the hope that the intermittent problem would become a permanent one that would thus be easier to diagnose. I wasn't disappointed, after a few more hours sync was lost and no amount of adjustment would lock on. I suspected the monitor chassis but to be sure I first removed he game PCB and ran it on the bench to verify the sync output was working - it was and thus the problem was with the monitor chassis.
On the bench the chassis exhibited the same sync loss problem. Waveforms 7 and 8 both looked off compared to the manual. Since IC2 (TDA2593) is socketed it was easy to swap out with a new one to eliminate it as a cause. There was no change with the new one. The sync input to IC2 looked bad and further investigation discovered TR1 (BC237) emitter looked OK but TR1 collector looked bad. Replacing TR1 (BC237) fixed the sync issue and the chassis was ready to go back into burn-in test.
A few more days of burn-in testing didn't encounter any more failures.