The pair of #63 flashers on solenoid 12 (right side of the playfield) will not light in solenoid test, while every other solenoid works, even after the driver transistors and their logic chip were replaced.

Solenoid 12 flashers dead: one of the two series bulbs is open

Cause: The two flasher bulbs are wired in series, so one open bulb kills both. A bulb can look fine and still be open.

Checks

• Pull both bulbs and check each one for continuity with a meter instead of trusting how it looks.
• Only if both bulbs are good, check the drive voltages through the driver stage.

Fix

• Replace the open #63 bulb.

Systems

• Williams System 11

Games

• High Speed

Related tips

• High Speed pop bumper dead in coil test, fires with tab grounded: bad driver chip
• Two flashers out together may be a series pair
• C-bank coil or flasher not working
• Right-side playfield GI out: a wire not seated in a new power board connector
• Flashers dead on early games: resistors broken on under-playfield flasher boards
• Whole groups of coils or all flashers dead: A/C select relay stuck
• Special solenoid fuse blows at power-up: a pop bumper switch held closed
• Right sling locks on at power-up and a pop is dead: bad 7402 at U45

Source: Pinball Repair help group!! (Facebook group)