Mist multiball stops working because the long opto never registers; with the optos unplugged, all four opto pins on the board read close to 12 V.

Mist multiball long opto board dead: check L1 and the MPS-A77 transistor

Cause: Most often the L1 choke has a broken leg or has fallen off. Otherwise the Q1 Darlington transistor (MPS-A77) has drifted out of spec, sometimes along with one of the ICs. Leaking capacitors can also eat the 12 V trace that runs under them.

Checks

• Press gently on L1 each way; a broken leg usually shows at the top of the board. Make sure it is present at all.
• Look for capacitor leakage and corroded joints, and buzz out the 12 V trace near the capacitors.
• Test Q1; note that it can pass a basic diode test and still be bad.

Fix

• Resolder or replace L1 if it is cracked or missing.
• Replace the leaking capacitors and repair any damaged traces.
• If it still does not work, replace Q1 with a new MPS-A77.

Systems

• WPC Fliptronics

Games

• Bram Stoker's Dracula

Related tips

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• New lock optos fitted: those and other optos on the same plug stop working
• Egg target optos dead after fitting replacement opto boards: refit original receiver

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