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Pre-show testing found the game with no base missiles, but enemy missiles were displaying OK. The game PCB was removed for repair.
Checking IC 5R (LS163) pin 9 MLD was running OK. IC 4R (LS161) pin 15 output looked like a clock and IC 4P (LS10) pin 8 output was high with a low pulse on missile. I'd already had to replace several 74LS161 on this PCB and suspected IC 4R was bad. Connecting the HP-10529A comparator flagged IC 4R as bad. A quick piggy-back check with a replacement LS161 didn't fix the missing missile but the overtone of a signal moving with the missile could be seen on pin 15 with the scope. Replacing IC 4R (LS161) fixed the missing missile.
During bench testing it became clear that many of the sounds had become high pitched. Pitch high nibble counter IC 8K (LS161) had already been replaced and using the HP comparator again flagged the pitch low nibble counter 9K (LS161) as bad. At this point I'd had 7 of 10 Signetics 74LS161 date code 7925 fail on this PCB and I decided to replace all the remainder. Replacing IC 9K fixed the sound pitch.
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More bench testing revealed that the game would occasionally exhibit graphics corruptions & crashes. Testing with the Arduino ICT "RAM Check All" option flagged "E:7N 7000 90 80". A "RAM Write-Read" test confirmed data bit 0x10 was intermittent. Replacing IC 7N (2114) fixed the test failure but the game was still having boot issues. The Arduino ICT didn't yet support the multi-games interrupt configuration but with CPU Z80 pin 17 NMI and pin 16 INT were both active. I was beginning to wonder if there was a bus loading issue. "Bus Check" flagged "E:D0 ff ef", the same bit flagged as had been flagged as intermittent in the RAM check. The data bus buffers were a pair of 8216, and a similar pair in the video circuit had already been replaced with the alternate 74LS245 option. Replacing IC 8H & 8F (8216) with 74LS245 fixed the bus check and the game ran OK for several hours on the bench.