Do not hesitate to contact me if you have a question or a problem. You may find the Tech Support Articles below helpful for many common issues.


If your DewBuster™ Controller is not working properly see Troubleshooting Problems.
New DewBuster™ Controller owners may want to familiarize themselves with its operation prior to their first night under the stars. This can be done indoors and does not require setting up your mount, simply put the heater strips on your telescope. If done outdoors, shade the telescope so the sun won't heat it and prevent the heaters from turning on. 
  1. Attach Temperature Sensor to your main heater and place the heater on your telescope as directed in the owners manual.
  2. Plug the DewBuster™ Controller into your power source and set control knob to 5°F (warmer than air temperature).
  3. Since the telescope is cooler than desired, the TEMP CONTROLLED output's LED will turn on constantly (100% power) to warm the telescope.
  4. When the telescope has warmed 5°F above the air temperature, the TEMP CONTROLLED output LED will start blinking (reduced power) to maintain the temperature.
  5. Turn control knob to 10° and TEMP CONTROLLED output's LED will go to full power until the scope warms to the new setting.
  6. Turn control knob back to 5° degrees and LED will turn off until telescope cools down.

  7. Now try manually controlling the MEDIUM POWER outputs:
  8. Unplug Temperature Sensor and set Control Knob to 0. Notice the red LED blinks steadily.
  9. Vary the Control Knob between 0 and 15 and notice the blink rate does not change. When a Temperature Sensor is not being used the DewBuster™ Controller will not reduce power below 40% which provides enough extra power to prevent dew without measuring the temperature.
  10.  Now vary the Control Knob from 15 to 20 and notice the power level increases (LED remains on longer). The DewBuster™ Controller is in MANUAL mode which allows you to increase the power level above 40% when a Temperature Sensor is not being used.
  11. Now turn the Control Knob to fully clockwise and notice the power level increases to 100%  (LED remains on constantly). The DewBuster™ Controller is in DEW BURN-OFF mode which is useful if dew has already formed and must be removed.
You should now have a good feel for how the DewBuster™ Controller works. Remember:
  • TEMP CONTROLLED output's LED should blink (set temperature reached).
  • MEDIUM POWER output's LED blinks (unless Control Knob is fully clockwise).
How can I test my DewBuster™ Controller if it does not seem to be operating properly?
  • First unplug the temperature sensor and all heaters. Turn off the DewBuster™ Controller, and plug it into your power source. All lights should be off.

  • With sensors and heaters still unplugged, turn on DewBuster™ Controller and set control knob to zero. The LEFT and RIGHT LEDs should blink, if not then check for a blown fuse in the cigarette plug (unscrew tip to access fuse).

  • Plug one Temperature Sensor into DewBuster™ Controller but DO NOT plug the heater in. Set the control knob to 5 degrees and allow both the Scope Sensor and Air Sensor to hang freely in the air so they both reach the air temperature. Wait several minutes until the red LED associated with the Temperature Sensor stays on continuously (it thinks scope is at air temp and turns heater on to warm scope 5 degrees above air temperature). Grab the Scope Sensor (the little bumps under the black heat shrink covering) with one hand so that your thumb presses against the little bumps of the Scope Sensor and as your body temperature warms it the red LED should turn off (it thinks the scope is warmer than the air so it turns the heater off). While still holding the Scope Sensor in one hand, grab the Air Sensor between your thumb and index finger of the other hand and after several seconds the red LED should turn on (it thinks the scope and air are the same temperature so it turns on heater to warm the scope). Also inspect the Scope Sensor to insure the wires are not protruding through the black heat shrink (if they are, then place a single layer of electrical tape over the damaged area to prevent the wiring from touching any metal on the telescope as this can interfere with sensor operation). Move the sensor to the opposite side's input and repeat the test. If you have more than one sensor test each one. Note: a damaged or malfunctioning sensor may sent in with $5 to cover return shipping and it will be repaired free of charge, contact me for return instructions.

  • Now clip the temperature sensor onto your main heater and attach the heater to your telescope (be sure Scope Sensor is placed against the telescope as shown in the DewBuster™ Controller owners manual). Set Control Knob to 10 but do not plug in any Temperature Sensors. Plug main heater strip into Temperature Controlled output and verify red LED on that side continues to blink (if LED goes out or dims when heater is plugged in then you have a shorted heater). Test each of your other heaters for shorts by plugging them into the Temperature Controlled output and verifying that LED continues to blink.

  • With Control Knob still set to 10 and only the main heater plugged in with its LED blinking: Plug-in the Temperature Sensor that is attached to the main heater. Its red LED should turn on continuously while the heater warms the telescope 10 degrees above air temperature. Once the temperature is reached the LED will start blinking or cycle between on and off. If the LED stays on all the time this means the heater is not warming the telescope up enough (for SCT's be sure you are using a dew shield and the heater is behind the corrector plate casting, not on the casting itself). If LED stays off all the time but blinks when Temperature Sensor is unplugged then this means the telescope is warmer than the control knob setting (be sure the Scope Sensor is on the same heater that is plugged into the Temperature Controlled output on that side).
If the above instructions do not produce the expected results, then contact me and describe what happened when you performed the above tests.
How can I tell if the DewBuster™ Controller is maintaining the temperature where I have it set?
The Temperature Controlled output's red LED blinks when the telescope is at the set temperature. If LED is off that indicates telescope too warm (no power applied so telescope can cool). If LED is on constantly that indicates the telescope is too cold (full power being applied to warm the telescope). Under normal operation blink rate varies as controller adjusts power level to control telescope temperature and LED may even stop blinking or remain on for short periods of time. However if LED never blinks then check that Temperature Sensor is making good contact with the telescope, the Air Sensor is not touching anything, and the corrector plate (or objective) heater is plugged into the Temp Control output that the sensor is controlling.
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 illuminate (assuming a good battery). Make sure each heater gets warm after about a minute. No matter how small a heater is, if it is working it should get warm to the touch. If you find a heater that is not working, don't throw it away, the problem is usually in the RCA plug and is very easy to repair.

Does the DewBuster™ Controller have a fuse?
Cigarette plug models have a fuse in the tip of the plug. If the LED light in the plug is not illuminated (the light is dim so it will not interfere with your night vision) and you are sure that the socket has power, then unscrew the tip of the cigarette plug and check for a blown fuse. The standard fuse is an AGC 5 Amp but up to a 10-Amp fuse may be used if your cigarette socket can handle the current. These fuses are available at any auto parts dealer. The spring location is very important and differs between the 2 types of cigarette plugs (refer to picture above) so  insure that it is replaced properly, otherwise a poor connection will be made and the yellow Low Battery light may come on.

Heavy Duty Power Cord models have a 16 Amp solid state "PTC" fuse which self-resets when the controller is unplugged for a few minutes. If you have a Heavy Duty power cord with a cigarette plug then the cigarette plug will also have a fuse which is replaced as outlined above.

Big Dob models have a 10 Amp solid state "PTC" fuse which self-resets when the controller is unplugged for a few minutes. The optional RCA to cigarette plug power cord will also have a fuse which is replaced as outlined above.
The yellow LED illuminates when the voltage at the DewBuster™ Controller falls below 11.0 volts. This normally means the battery is low on charge, but it can also be caused by poor electrical connections which cause voltage losses and result in lower voltage at the DewBuster™ Controller than at the battery terminals. The following instructions will help you to determine where any poor connections are located as well as if you have a shorted heater drawing excessive current.
Check for a shorted heater strip as follows:
  • Unplug all heaters, unplug temperature sensors, and turn the control knob to maximum so the DewBuster™ Controller sends full power to all heater outputs and keep it in this setup for all of the following troubleshooting because you will only see voltage drops when maximum current is flowing.
  • While observing the yellow Low Battery light and red LED, plug each of your heater strips into either the left or right Temperature Controlled output jacks and if the Low Battery light comes on and or the red light dims or goes out that heater may have a short in it. The heaters that did not cause the Low Battery light to come on are OK.
  • If several heaters caused the Low Battery light to come on then it is not likely that they all have shorts in them. If your DewBuster has a cigarette plug make sure that it is full inserted into the cigarette socket as they tend to work loose. Check if your power source is able to supply enough current to operate your dew heaters or you have a bad connection. Power supplies rated less then 5 Amps are not suitable for dew prevention. If you are powering from a battery, the AH rating should be at least twice your largest sized heater (17AH for an 8" SCT).
  • If only your largest heater caused the Low Battery light to come on then it may be a poor connection in your power wiring. This will be checked below.
  • If your largest heater does not make the Low Battery light come on but a smaller heater does, then that heater may have a short in it. If you have an ohmmeter check the heater resistance. Even the largest heaters should read more than 2 ohms and most heaters read around 10 to 40 ohms. If you find a heater has a short in it then see my instructions for fixing heater shorts.
  • Shorts may be intermittent so if the yellow Low Battery light did not come on with all heaters plugged in, then try gently wiggling and twisting each heater cable near the RCA plug to see if this makes the yellow light come on. If it does then see my instructions for fixing heater shorts.
If the yellow LED did not seem to be caused by a shorted heater, then it may be that the power source, wiring, or connections are causing the problem.

Turn the control knob fully clockwise and plug in all heaters so that maximum current will flow as you take the following voltage measurements:
  • Measure the battery voltage directly at the battery posts. This voltage should be above 12.5 volts on a fully charged battery under load. If the voltage at the battery posts drops below 12.0 volts then the battery needs to be recharged or it is not able to handle the current flow. If you suspect your battery may be failing, check how long it takes to recharge. Batteries are rated in AH which is the Amps multiplied by the time in hours that the battery can supply that number of Amps. So a 17 AH battery can store enough energy to deliver 1 Amp for 17 hours, or 17 Amps for 1 hour. The same formula applies when charging, so check the label on your battery charger to see how many Amps it can charge at then time how long it take to recharge the battery when it has run down. So a 1 Amp charger should take about 17 hours to fully charge a 17AH battery. If this  battery recharges in less than an hour, then that battery is only storing 1/17 the energy and should be replaced. Keep in mind that if the battery is only 50% discharged then it will recharge in half the time because it is already half-way charged.
  • If you are using a power supply, take the measurement at the output terminals of the power supply. If the power supply voltage is below 12.0 volts then it is probably not big enough to provide the current being used by the heaters. You will need to obtain a power supply that can provide sufficient Amps. If you want to verify that the controller is working, then try plugging the controller into the cigarette socket in your car while the engine is running and the yellow light should not come on.
  • If the battery voltage was OK in the above test, then measure the voltage at the DewBuster™ Controller (see diagram above) by touching the red lead to the inside of any RCA jack and the black lead to the outside terminal of the RCA jack. If the voltage at the DewBuster™ Controller is less than battery voltage then this indicates a voltage loss in the wiring or connections. If so, then measure the positive and negative side voltage drops as shown in the diagram above. With a large dew heater strip the positive side may read up to 0.5V drop and the negative side may read up to 0.1V drop. If there is a larger drop then there is a problem. By measuring the voltage across each connection, switch, fuse, etc. you can determine where the voltage losses occur.
After performing the above checks, if you have not isolated the problem, contact me with the results of the above tests and I will help you figure out the problem. Be sure to include your Serial Number as this helps me to interpret your readings.
This procedure is harmless and highly recommended to maximize reliability of your equipment, however if your heater is under warranty this may invalidate that warranty.

If your dew heater does not have a metal RCA plug as shown below, then these instructions do not apply and the RCA connector is probably NOT the problem.

On some Kendrick Heaters, there is no insulating material separating the + and - terminals and repeated tugging and flexing of the heater cable may eventually cause the connections to touch intermittently, causing shorts. To check for this condition do the following:

Unscrew the barrel of the RCA plug and slide it out of the way to allow inspection of the connector:
GOOD: Heat Shrink Insulation on center terminal prevents it from touching outer terminal and keeps the terminals separated. Reassemble the connector by sliding the outer heat shrink back over the connections and screw the barrel back on. You are finished with this heater, but be sure to check your other heaters. If the connections look like either of the photos below, then the plug can short and you should repair it as directed below.
image image
BAD: Heat Shrink Insulation is on outside of connections so it does not keep terminals from touching together. If the heat shrink covers the terminals, slide it back to reveal the electrical connections within.


The photo above shows what is beneath the heat shrink, the terminals are almost touching and can short when the cable is flexed.

The photo above shows the RCA plug after wrapping electrical tape around the center terminal. This prevents the center terminal from coming into contact with any other parts of the plug. The outer terminal does not have to be insulated since it is connected to the plug housing anyway. If you have any questions, contact me  for assistance.  

IIf you need to repair, replace, or change the connector on your DewBuster™ Controller the following the information will prove helpful. And rest assured that simply modifying your power cord will not void your warranty.

Low Voltage Landscape Lighting Cable is readily available at hardware stores. It is relatively inexpensive because it is only rated for 12 volts yet is durable and weather resistant. Do not make the power cord any longer than necessary, instead of lengthening the 12VDC wiring it is better to locate the power supply as close to the telescope as possible and run longer extension cords. If your telescope has any large heaters, use #14 or #12 wire when increasing power cord length for reduced wire resistance.
  • If using a larger gauge wire, cut the DewBuster™ Controller's power cord about 6 inches from the controller to get rid of as much of the smaller gauge wire as possible. Connect the landscape cable to the DewBuster™ Controller's original power cord (use a Powerpole® connector or solder the wires for low resistance connections). The DewBuster™ Controller's power cord has ribs on the positive wire and should be connected to the Landscape Cable's ribbed wire.
  • If you are reusing the cigarette plug, it is very difficult to solder the wires inside the plug so I recommend cutting the wire about 6" from the cigarette plug and soldering it to the landscape cable (match the ribbed wires).
  • If your battery or power supply can accept banana plugs or ring terminals, they will make much better low-resistance connections than a cigarette plug. If your DewBuster™ Controller was originally equipped with a standard duty cigarette plug power cord and you are connecting to a battery, then you will need to add a fuse holder and AGC 10 Amp fuse in the positive wire as close to the battery as possible. If you are connecting to a power supply then it should already be fused, in which case  you do not need to add another fuse. All DewBuster™ Controllers equipped with Heavy Duty power cords have a PTC fuse inside the DewBuster™ Controller so there is no need to add another fuse.
  • Test the new power cord by unplugging all heaters, 12V accessories, and sensors then attaching the DewBuster™ Controller to your power source. Turn the control knob on and if the red LED's start blinking then you were successful. If the controller does not turn on (red LED's and yellow Low Battery LED remain off) then you probably have the + and - wires reversed. Don't worry, no harm will be done because the DewBuster™ Controller is reverse polarity protected, just correct the wiring and the heater lights should blink.
  • If the DewBuster™ Controller's yellow Low Battery light starts coming on after extending the cable, then you either have poor connections or the wire gauge is too small for the length you extended it. While it is tempting to add cigarette sockets to the extended power cord, a device plugged into these sockets would experience voltage dips when the dew heaters turn on and off. If you want to add extra cigarette sockets then it is better to run a separate set of wires from the battery to power the extra cigarette sockets.
The DewBuster™ Controller's Temperature Sensor cable has a 6 foot long striped gray cable that connects to the DewBuster™ Controller via a phono plug. The temperature sensor portion should not be modified but the gray cable between the DewBuster™ Controller and temperature sensors is an ordinary 2 conductor copper wire and its length may be extended several feet by simply cutting it and soldering in an extension wire. I do not recommend extending the wire more than a few feet. The plug is a standard 3.5mm mono plug like those commonly used for earphones and is easily replaced if it becomes damaged. The gray striped wire connects to the tip of the phono plug.
After modifying or repairing the Temperature Sensor Cable, test it's operation as follows:
  1. Plug the DewBuster™ Controller into 12-Volt power but do not plug in any heaters.
  2. Plug the Temperature Sensor Cable into the DewBuster™ Controller but do not attach the Temperature Sensor to the telescope. Instead suspend the Temperature Sensor in the air for several minutes so both Scope Sensor and Air Sensor can acclimate to the air temperature. Do not touch them with your hand as your body temperature would warm them.
  3. Turn the DewBuster™ Controller knob to 0 degrees.
  4. Wait about 5 minutes for the Temperature Sensors to cool to the air temperature.
  5. Increase the DewBuster™ Controller knob to 5 degrees and the Temp Control LED should come on and stay on.
  6. Simulate the telescope warming up by touching the scope sensor with your thumb. After a short time the Temp Control LED will start blinking and then go out completely.
  7. While still holding your thumb against the Telescope Sensor, grasp the Air Sensor between two fingers of your other hand. After a short time the Temp Control LED will turn on and stay on.
  8. If steps 6 and 7 worked, then you have the wires connected properly.
  9. If in steps 6 and 7 the Temp Control LED worked backwards, then you have the wires reversed on the new plug. Correct the problem and test again.

Any closed-tube telescope will have air trapped inside, and all air has some amount of moisture in it and hence a dew point. The air trapped inside will cool as the telescope cools during the night, and when it cools to its dew point temperature, moisture will begin to condense onto the interior optical surfaces. The problem is at its worst on cold winter nights because the night air temperature gets much colder than the dew point of the air inside the OTA.
How does moisture get inside your telescope?
Warm air absorbs a great deal of moisture and when that air cools down it will release the moisture as condensation. Do not uncap your telescope indoors or during the day to "dry up" the interior moisture because the warm air's dew point is well above the coldest temperature that will be reached that night. This means that when the air inside cools at night moisture will begin forming on the interior optical surfaces again.
So how can we stop moisture from forming inside the telescope on cold nights?
Instead of trying to dry the telescope during the daytime when the dew point is at its highest, do it at night when the dew point is lower. If moisture forms on the inside of the OTA at night, remove the eyepiece/diagonal and point a hair dryer toward the rear opening of the telescope so that it blows warm (not hot) air into the telescope. Do not press the hair dryer directly to the eyepiece opening, keep it several inches away so that no pressure builds up (a hair dryer will overheat if there is no air flow) and pause as needed so the rear opening won't get too hot. An SCT corrector plate has air gaps around it so the warm air will absorb moisture and escape around the corrector drying out the inside of the OTA.
For a more elegant solution than a hair dryer, the Lymax SCT Cooler circulates air through the telescope so it can be used early in the evening to cool the scope and late at night to remove any damp air. If you prefer the build-it-yourself approach, take a look at:
How do we keep moisture from getting back into the telescope?
The best way is to keep the low humidity air trapped inside the telescope by capping up the eyepiece end of the telescope before bringing it in from the cold night air. It is OK to uncap the objective lens or corrector plate, but do not uncap the eyepiece end as you do not want to let the dry air escape from the interior of the telescope.

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