The 6803 does not run; U1 pin 6 is not at +5 V after power-up.

CPU never starts: check the reset line at U1 pin 6

Cause: Failed part in the reset circuit, which is fed from +12 V through Q2 and Q3; C1 charging switches Q4 and Q5 to raise pin 6.

Checks

• At power-on, U1 pin 6 should dip to 0 V briefly while +5 V settles, then go high and stay high.
• Check reset parts Q2/Q4/Q6, capacitor C1 (6.8 mfd, non-polarized), Q3/Q5 (2N4403), zener D1 (1N958B, 7.5 V), D3 (1N4148) and D4/D5.

Fix

• Replace the failed reset parts.

Systems

• Bally 6803

Related tips

• CPU LED stops just short of the full count
• Game boots but will not take credits or start
• Expected CPU LED flashes by game
• How to read the flashes on pre-1988 6803 games
• How to read the flashes on the last four 6803 games
• Nonsense adjustment values after a battery failure
• Missing lamp fuse changes the flash count
• Eight-flash LED code meanings

Source: Repairing Bally 6803 Pinball Games from 1985 to 1989, Clay Harrell (pinrepair.com)