RJC‑6 Controller Blows Fuse, Then Loses All Power After Larger Fuse Installed

An RJC‑6 controller started blowing its fuse. The owner installed a larger fuse, after which the controller had no power at all.

What Happened

The original fuse blowing indicated a short circuit—usually a faulty solenoid or damaged field wiring. Installing a larger fuse allowed excessive current to reach the controller’s circuitry, likely frying the board.

Next Steps

1. Check transformer output with a multimeter (should be 22‑26 VAC). If voltage is correct but the display stays dead, the controller is damaged.
2. Replace the controller with a model that has an internal circuit breaker, such as the Irritrol Rain Dial, which protects against field shorts.
3. After replacement, test each zone individually to identify the shorted solenoid or wire.