The LiftMaster 21-3240-1 is an OEM step-down transformer engineered to supply low-voltage control power to select LiftMaster commercial door and gate operators. Featuring a dual 120/240V primary and 24V secondary, this replacement transformer restores stable power to control boards, relays, photo-eyes, keypads, radio receivers, and other accessories. As the exact LiftMaster replacement part (21-3240-1), it provides the proper 24V output the operator’s logic circuit is designed to receive, helping ensure reliable operation and compatibility in professional service and maintenance applications.
Intended for installation inside the operator housing, the 21-3240-1 transformer should be fitted by a qualified technician. Always disconnect power, confirm incoming line voltage, and connect the correct primary leads for 120V or 240V per the operator’s wiring diagram, then route the 24V output to the designated control terminals. Common signs of a failed control transformer include a dark control board (no LEDs), nonresponsive accessories, or repeated low-voltage fuse issues. This OEM LiftMaster transformer is used on select jackshaft, trolley, and hoist commercial operators and some gate operator control boxes; verify fitment against your model’s parts list or LiftMaster technical support before ordering. Relevant search terms: LiftMaster transformer 21-3240-1, 120/240V primary 24V secondary, control transformer, commercial door operator replacement part, gate operator transformer.