My Door Chime Striker Piston Will Not Work

Solenoids

• An electrical solenoid converts a pulse of direct current to mechanical force. When current flows through a copper wire, an electromagnetic field forms. Winding many turns of wire into a coil intensifies the field. Placing an iron or steel core in the core makes the field stronger and temporarily magnetizes the core. If a magnetic part lies in a fixed position close to the core, the core moves and closes the gap. Solenoids exploit this by placing a spring between the core and its magnetic partner. An active solenoid compresses the spring, bouncing back to the original position when the current stops.

How Chimes Work

• Door chimes that incorporate solenoid strikers typically use power supply transformers that step down 120 VAC to 16 VAC. Additional circuitry converts the 16 VAC output to a pulse of direct current when the doorbell button activates. With all the other electrical components working properly, the DC voltage across the solenoid coil causes the striker to move. One-note strikers strike a chime in one movement, while two-note strikers ring one chime on the active movement and a second chime when springing back. Faulty solenoids receive the right input pulse but fail to ring the chime for either electrical or mechanical reasons.

Electrical Faults

• A solenoid might fail because of corroded or tarnished electrical connections. As oxide builds up, twisted-wire connections sometimes fail. Soldered connections should last if finished correctly, but cold-soldered joints suffer the same problems as wire wraps. Wires in a good solder joint make a strong mechanical connection, with solder flowing between the wires. A rounded blob of solder enclosing the wires indicates a cold joint and might cover insulating oxide. Daubing the cold joint with flux, and reheating until solder flows properly, repairs the connection. Repair twisted-wire connections by polishing the wires with emery cloth and re-connecting with wire nuts.

Broken Parts

• Coils might not activate because of internal faults. Disconnect one lead of the solenoid to measure the coil resistance with a volt/ohm meter. Resistance should measure almost zero. High resistance indicates a broken wire.

  Strikers can tarnish and stop moving freely through the coil. By disconnecting the return spring, you can remove the striker and clean the surface with metal polish. Any residue adds to problems, and oil can completely jam the mechanism.

  Shorted coils reduce the solenoid's power, but volt/ohm meters won't reveal that fault unless you know the length and resistance of the wire in the coil. Strikers with plastic tips sometimes break or wear down. In either case, a replacement part is the best fix.