12v Battery Charger Zero Power output and Smoking Transformer

Thread Starter


Joined Dec 14, 2020
I would like to learn if this is #1 repairable and #2 worth repair. Smoking transformer on Inexpensive Chicago Electric Battery Charger.
Model 66783 Chicago Electric Battery Charger that used for charging either 6 or 12 volt batteries. I would like to understand what caused the transformer to start smoking and stop producing output voltage with loud humming and if possible to repair. This has happened on two separate chargers the exact same conditions 6 years apart. I have started trouble shooting with digital multimeter but have not found the component (s) that has failed to cause this.

Model 66783 has 6v10A , 12v 2A, 12v 10A, 12v 55A settings but I only use the 2A and 10A settings to charge 12 v batteries. Both primary and secondary windings heat up but appears the primary winding is smoking during the last use to charge a 12 v lawn mower battery and then I started the lawn mower and the battery charger was on momentarily and started to hum loudly and then smoke before disconnecting the negative battery spring clamp. The 12v 20A thermal fuse is still testing continuity, both diode buttons show no burning on the contacts with the aluminum sheet or wire connectors, I cannot see any enlarged or blown capacitor either. Any help to determine if this is worth repair as I enjoy learning. Images for the transformer both ends, circuit board, thermal fuse and rectifier are attached.

Where do I go from here if any can walk me through steps I would be grateful.20201214_131418.jpg20201214_131450.jpg20201214_131409.jpg20201214_131432.jpg20201214_131418.jpg20201214_131450.jpg20201214_131409.jpg20201214_131432.jpg20201214_131418.jpg20201214_131450.jpg20201214_131409.jpg20201214_131432.jpg


Joined Jun 22, 2012
Disconnect the two Red wires on the Secondary side and measure the voltage on AC across each terminal and the Black centre.

Also with power switched off, check on Diode test the dual diodes on the heatsink.


Joined Jun 4, 2014
That dual diode doesn't looks like it is not pressed firmly onto the heatsink. If that is the case it may have led to overheating of the diodes and ended with them being short circuit.