The match shows the same number every game, or an alternating feature light stays always on or off.

EM match unit stuck on one number

Cause: The small match unit in the backbox is dirty and sticky, or its relay-driven plastic pawl slips off the gear, is dirty, or has lost its spring.

Checks

• Operate the match relay by hand and watch the gear advance a notch each time.
• Check the pawl and its spring.

Fix

• Clean the gear with alcohol on a cotton swab; do not use WD-40 on the plastic.
• Remove and dismantle the unit if needed, sketching the parts order.
• Refit or replace the pawl spring.

Systems

• Electro-mechanical

Related tips

• Williams 1970s match unit stops advancing
• Bally 00-90 match unit
• How the EM match feature works and is disabled
• Game gets stuck on player 2: sluggish player unit
• Gottlieb 4-player shows players 1 and 4 lit at start
• Player 1 'up' lights stay off during play: clean the coin unit contacts
• Game will not work: stepper unit binding
• Ball count drops by one as the first ball is served: stuck 10-point playfield switch

Source: Pinball Machine Care & Maintenance, Bernard B. Kamoroff (Bell Springs Pinball Alley)