4.92 is really on the low side of acceptable, especially for a game like TZ. I'd try to get it up to 4.95 or higher. Also check the 5 volts at pin 32 of the game ROM. Some games use an inline splice between the CPU and driver, and I believe TZ is one of them. That connector is notorious for causing a voltage drop.
Most people also don't replace C4, which costs about 25 cents and can make a sizeable difference in the +5.
On real problem boards, I isolate the case of the LM323 from the driver board, and install a 22 ohm 1/2 watt resistor between the case and ground. That bumps the 5 volts up to about 5.1-5.2 volts.
