One of my Pole Position IIs worked great, except the player's engine sound was missing. I searched all over for this, and was mostly only able to confirm that it happens to others. The ONLY successful fix I could find was this one on RGVAC, which was a bad 7497 at 11C.

Luckily, I had a working boardset to compare to, and I found out that I was missing the ADCLK coming from the 7497 at 12B (pin 6). This should pulse as soon as the player's engine starts to make noise. I replaced the chip and all is well.

So, based on my sample, 100% of the player's engine sound missing issues are caused by one of the two 7497s at 11C and 12B. If you have a logic probe, here is what I think you should see on those two chips DURING GAMEPLAY. These are oriented as you see them in the game, with pin 1 at the upper right. H=high, L=low, P=pulse, X=no connection.

11C
LPPHLLLH
PLLXLLLH

12B
LXPHLHHH
PPPPLLHH

The bold P on 12B was my issue.