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Submitted for the first time into the show the game ran for the first couple of days but by Sunday the monitor had lost sync and wouldn't adjust to sync lock :(
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I pulled the chassis from the cab to test on the bench suspecting it was a monitor issue rather than a board issue. The output of TR1 (BC237) looked poor. Replacing TR1 brought back horizontal sync lock but the vertical sync lock was out of phase, "ami Kon" rather than "Konami" in the center of the screen. Swapping out the TDA2593 made no difference. Tweaking the vertical sync pot did fix the vertical sync phase lock, but the pot was very sensitive to adjustment. The pot resistance measured OK and once set it stayed locked for several hours so I decided to return it to the cabinet. Back in the cabinet the sync lock showed no issues and thus I declared the chassis fixed.
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The game ran for a few minutes during pre-show testing before the monitor died. Suspecting an HV shutdown, after a power cycle the monitor came back on but after a few minutes it shut down again. Subsequent power cycles didn't bring the monitor back, it was dead. There was no HV or neck glow so I pulled the chassis for repair.
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The B+ voltage measured a stable 126V DC and thus seemed OK. The TDA2593 bootstrap voltage on pin 2, notionally +12V, measured 6.8V and from prior measurements during previous chassis repair seemed to be the "normal" bootstrap voltage.
I moved on to test point 3 in the manual, the horizontal LOPT drive signal. The signal on the scope was pretty close to the example in the Hantarex manual thus the chassis was not in HV shutdown - the TDA2593 was outputting a signal. Moving forward to the drive transistor TR10 (BF419) found no collector output. Pulling out TR10 to test confirmed that the transistor was bad. Prior chassis such as the MTC-900 & MTC-90 utilized a BF459 for the line drive transistor so I had recycled spares for those transistors. Comparing the datasheet for the BF419 vs BF459, the major difference appeared to be that the BF419 was rated 250V and BF459 was rated 300V. Since the circuits were otherwise almost identical on previous chassis I theorized that the change to the lower voltage was for cost saving reasons and thus the BF459 would be a suitable alternative (I had not seen this transistor fail on any other chassis, mostly MTC-900 with BF459 fitted). Replacing the bad BF419 with a BF459 brought the chassis back to life.
There was one additional issue with the picture having unstable red brightness. I'd seen this problem on the 900E series a few times now, typically caused by a bad transistor in the colour pre-amplifier stage. I decided to try a drop of freezer spray on each transistor in the red circuit and got a hit on TR20 (BC547 == BC237). Replacing TR20 fixed the red drive and the chassis ran on the bench for a few hours with no further issues.