Several switches suddenly stop working together (here Start City, all three Blast Zone switches and an inlane).

Several unrelated switches stop at once: one broken wire under the jet bumpers

Cause: A white/green wire had broken off a switch above the jet bumpers. Switch wires are daisy-chained from switch to switch, so one break kills every switch further along that chain.

Checks

• Look the dead switches up in the switch matrix chart: if they share a row or column while others on it still work, suspect a broken wire under the playfield rather than the CPU board.
• Lift the playfield and follow the shared wire colour from switch to switch, looking for a wire off a lug.
• If no switch on that row or column works, check the CPU switch connector (J209) and the board.

Fix

• Resolder the broken wire to its switch lug.

Systems

• WPC DCS

Games

• Red & Ted's Road Show

Related tips

• Several switches in one row never register: broken row wire at another switch
• Spinner stops registering: broken wire on an upper flipper EOS switch
• Several switches in one row or column dead: a broken daisy-chain wire
• Two or more unrelated switches trigger together
• Most of switch row 6 dead, last switch works: broken row wire
• A whole switch column stops working: replace the ULN2803 column driver at U20
• A replaced switch registers under the wrong number
• After a new U20, work every flagged switch once

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