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Does the DewBuster™ controller have a fuse?
DewBuster™ controllers with a cigarette plug have a fuse in the tip of the plug. It is accessed by unscrewing the end of the cigarette plug. The fuse is available at Radio Shack. The standard fuse is a 5-Amp fast-blow fuse. The cigarette plug is rated for 10 Amps so up to a 10-Amp fuse may be used if your cigarette socket can handle the current (most can not handle more than 5 to 7 amps).
DewBuster™ controllers ordered with the Ring Terminal Option have a solid state self-resetting fuse within the controller. If the fuse trips, disconnect the controller from the power source for a few minutes to reset the fuse.
How can I tell if the DewBuster™ controller is maintaining the temperature where I have it set?
If the AUTO light is blinking then the telescope is at the set temperature. Under normal operation the blink rate will vary as the controller adjusts the heater power level to control the temperature. The AUTO light may occasionally stay off (telescope needs to cool) or on (telescope needs to warm up) for a short while, but it should resume blinking. If the light remains on check that Telescope Sensor is making good contact with the telescope, the Air Sensor is not touching anything, and the corrector plate (objective) heater is plugged into the AUTO output.
How can I check my heater strips?
If you have a multimeter, measure the resistance of your heaters to make sure they are not shorted or open. A 14" heater will measure about 2.5 Ohms, 8" to 12" heaters 4 to 8 Ohms, 3" to 5" heaters 10 to 20 Ohms, and small heaters 20 to 100 Ohms. As you can see, the larger the heater the lower its resistance should be, but no heater should read less than 2 Ohms unless it has a short in it.
Now turn the DewBuster™ controller to maximum and one at a time, plug each heater into the DewBuster™ controller. No heater should cause the fuse to blow or cause the DewBuster™ controller's yellow Low Battery LED to turn on (assuming a good battery). Make sure each heater gets warm after about a minute. No matter how small a heater is, it should get warm to the touch if it is working. If you find a heater that is not working, don't throw it away, the problem is usually in the RCA plug and it is very easy to repair.
How do I check that my DewBuster™ controller is operating properly?
First unplug the temperature sensor and all heaters. Turn off the DewBuster™ controller, and plug it into your power source. The AUX, AUTO, and LOW BATTERY lights should remain off.
Next, turn on the DewBuster™ controller but leave the temperature sensor unplugged and set the control knob to zero. The AUX light should flash, if not then check for a blown fuse in the cigarette plug (unscrew tip to access fuse). If fuse was replaced, then turn off controller and insure all lights are off.
Slowly increase the control knob setting and the AUTO light will flash faster until it stays on continuously. Keep increasing the temperature setting until the AUX light stays on continuously too. If everything worked so far, then the DewBuster™ controller is working properly (see next section for checking heaters).
Plug the temperature sensor into DewBuster™ controller but do not attach it to your heater strip. Set the control knob to 5 degrees. With both telescope and air sensors exposed to the air, wait until the AUTO light stays on continuously. Grab the telescope sensor with one hand so that your body temperature warms it up. The AUTO light should start blinking and then go off (it thinks the scope is too warm so it reduces power to the heater). Now, while still holding the telescope sensor in one hand, grab the air sensor with the other hand. As your body warms the air sensor the AUTO light should start blinking and then stay on continuously (it thinks the scope and air are the same temperature so its trying to warm the scope 5 degrees above the air).
Now clip the temperature sensor onto your main heater, attach the heater to your telescope, and plug the heater into the AUTO output. If the AUTO light goes out or gets very dim then you have a short in the heater. If the AUTO light remains on then plug the temperature sensor into the DewBuster™ controller and set the control knob to 10 degrees. The AUTO light should stay on continuously until the heater warms up the telescope, then start blinking when the proper temperature is reached. If it does not work as expected, check that you have the sensor properly installed as shown in the DewBuster™ controller owners manual.