The eddy board LED stays on whatever the pot setting, so the switch never works.

Eddy board LED will not turn off at any pot setting

Cause: The R1 value leaves the pot outside its working range for that sensor.

Checks

• Check the R1 value against the game (2k ohm on Roadshow, 4.7k ohm on STNG).

Fix

• Change R1; in one Roadshow case R1 had to be replaced by a wire link (0 ohm) to centre the pot.
• Changing C1 to 3300 pF widens the sensing field a little.

Systems

• WPC DCS
• WPC-Security (WPC-S)

Games

• Red & Ted's Road Show

Related tips

• Adjusting an STNG, Theatre of Magic or Roadshow eddy sensor
• Eddy sensors: electronic ball switches under the playfield
• Indiana Jones to Demolition Man games have two LM339 opto boards
• Opto does not work: check 12 V at the transmitter connector
• Idol optos missing from switch test: use idol test, then fix connectors
• Roadshow: bulldozer blade won't go up in play
• Testing optos in switch edge test
• Flipper cabinet opto switch boards

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Three, Clay Harrell (pinrepair.com)