On a 1975 or later Ax/Bx Gottlieb, the tilt-hold, game over or first-ball relay is baked, or the game misbehaves in game-over mode.

Burnt H, Q and U continuous-duty relays on 1975+ Gottlieb

Cause: The H (tilt-hold), Q (game over) and U (first ball) relays stay energized the whole time the game sits in game-over. They are only about 30 to 35 ohm coils, and after decades most are cooked.

Checks

• Look for darkened coil wrappers and measure each coil; compare with the expected 30-35 ohms.

Fix

• Replace with the same relays (game over A-9740, tilt-hold A-9738, first ball A-9736), or
• Fit an orange A-16890 coil (220 ohms, the coin lockout relay coil from Gottlieb System 1 and System 80 games up to Hot Shots) wired as a DC coil with two 1N4004 diodes; it won't overheat and draws much less power. Gottlieb did this themselves on its last EMs.

Systems

• Electro-mechanical

Related tips

• Game Over (Q) and Tilt (T) relays are not fused
• Flipper stuck up with power on (Playboy and later)
• Relay coils used on System 80 games
• Check every coil's resistance before first power-up
• Check every coil's resistance before first power-up
• Solid state flippers, Robocop and later
• Fliptronics: flipper will not hold up (flutters)
• Row or column fault on the playfield

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)