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.


This assumes the DewBuster™ Controller is working properly, if not 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 in sunlight, shade the telescope so the sun won't heat it as this will prevent the heaters from turning on. This will give you a good feel for how the DewBuster™ Controller works.
  1. Attach one Temperature Sensor to main heater and place heater on telescope as directed in the owners manual. At this time keep the other sensor unplugged so that you can see how MEDIUM POWER works.
  2. Plug the DewBuster™ Controller into your power source and turn control knob to 5 which represents 5°F warmer than air temperature.
  3. Assuming telescope is the same temperature as the air, TEMP CONTROLLED output's LED will turn on constantly (100% power) until telescope warms up. MEDIUM POWER output LED will blink steadily since it is not temperature controlled.
  4. When telescope reaches 5°F warmer than ambient air, TEMP CONTROLLED output's LED blinks (reduced power) to maintain temperature. The Temperature Sensor is very sensitive and blink rate will change if your home's heating unit cycles on or if you cup your hands around the air sensor.
  5. Turn control knob to 10° and TEMP CONTROLLED output's LED will go to full power until the scope warms to new setting.
  6. Turn control knob to 5° degrees and LED will turn off until telescope cools to new setting.

    Now try "manual control" of MEDIUM POWER outputs when no Temperature Sensor is in use:
  7. Unplug Temperature Sensor and increase Control Knob to full clockwise position for "Dew Burn-Off mode" (useful for removing dew that has already formed). Notice that MEDIUM POWER output LED's (left and right since no sensors plugged in) stay on constantly (full power).
  8. Slowly reduce the control knob setting and notice that MEDIUM POWER output LED starts blinking  with a long duty cycle (ON TIME is longer than OFF TIME). As Control Knob is decreased the duty cycle decreases. With the control knob at 12 or below the MEDIUM POWER output will be 40% and ramps up to 50% at 15, 75% at 20, and 100% at full clockwise.
You should now have a good feel for how the DewBuster™ Controller works. The most important thing to understand is that the TEMP CONTROLLED output LED blinks when the desired temperature is reached. If LED stays on or stays off then something is wrong (check that temperature sensor is positioned properly). You should also understand that the Medium Power LED should blink unless the control knob is set fully clockwise to burn off dew.
When I turn on my telescope mount my DewBuster™ Controller LED's turn on and stay on?
In a few rare cases the telescope mount motors may create electrical noise that is picked up by the DewBuster™ Controller's Temperature Sensor and causes the Temperature Controlled channel's LED to stay on constantly. If the DewBuster™ Controller operates normally when the drive motors are off but the Temperature Controlled LED stays on constantly when the drive motors are on, then you may be experiencing this issue. Try moving the Temperature Sensor cables away from the RA motor and cables. If this does not resolve the problem then contact me for assistance.

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. 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 LED lights should blink, if not then check for a blown fuse in the cigarette plug (unscrew tip to access fuse). If fuse was replaced, then restart at beginning of these instructions.

  • Turn control knob to 15 then slowly increase setting and verify that the red LED's blink longer and longer (manual operation). When control knob is fully Clockwise the LED's should stay on continuously. If everything worked so far, then the DewBuster™ Controller is working properly, but continue with these instructions to test the heaters and sensors.

  • Plug the temperature sensor into either input on the 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). Move the sensor to the opposite side's input and repeat the test. 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 the metal telescope as this can interfere with sensor operation). Note that a damaged or malfuncioning 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 you are placing the Scope Sensor against the telescope as shown in the DewBuster™ Controller owners manual.  Set control knob to 10 but unplug all Temperature Sensors from the DewBuster™ Controller. Plug the main heater strip into the Temperature Controlled output and verifythe red LED on that side continues to blink (if LED goes out or dims when heater is plugged in but blinks normally when heater is unplugged, then you have a short in the 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 set to 10 degrees, only the main heater plugged in, and LED blinking: Plug-in the Temperature Sensor that is attached to the main heater strip. The red LED should turn on continuously while the heater warms up the telescope then start blinking in a few minutes when the proper temperature has been reached. In some cases the LED may not blink but may alternate between on and off due to time lag between heater and sensor, but it should cycle between on and off. If the LED stays on all the time this means the telescope is not warming up (for very large SCT's be sure you are using a dew shield and the heater is behind corrector plate casting not on it). 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 white Temperature Controlled output on that side).

If the above instructions do not produce the expected results, then contact me and include the results of 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 applied to warm 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./div>
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, 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 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 poor electrical connections can cause voltage losses as electrical current travels through them resulting in a lower voltage at the DewBuster™ Controller than at the battery terminals. Normal resistance in the DewBuster™ Controller's power cord and fuse may result in as much as 1/2 volt loss, meaning the low battery light could begin to illuminate when the battery is at 11.5 volts. If you have an elaborate power setup with switches, fuses, and other connections there will be a voltage loss as current passes through each item. The higher the current the greater the voltage loss so very large heaters on a cigarette plug power cord can cause problems. If a short develops in a heater strip this will cause a large current increase and can make the Low Battery light come on (as well as run your battery down quickly). 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.
  • One at a time, plug each of your heater strips into any of the heater output jacks (but not a 12V power output) while observing the yellow Low Battery light. If the light comes on when a heater is plugged in, then that heater "may" have a short in it so set it aside and continue checking the remaining heaters. 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  7 AH battery can store enough energy to deliver 1 Amp for 7 hours, or 2 Amps for 3.5 hours, or 7 Amps for 1 hour. Likewise a 100 AH battery can supply 1 Amps for 100 hours, 10 Amps for 10 hours, etc. The reverse holds true 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 it when it has run down. So a 0.7 Amp charger should take about 10 hours to fully charge a 7AH battery, and a 10 Amp charger should take about 10 hours to recharge a 100AH battery. If a either battery recharges in less than an hour, then that battery is only storing 1/10 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 it reads more then there is a problem. By measuring the voltage across each connection, switch, fuse, etc. you can determine where the voltage losses occur. A standard glass fuse in particular will cause a voltage loss due to it's internal resistance (this is why I use PTC fuses on the Heavy Duty Power Cords), and the smaller the fuse amperage the higher the resistance will be and thus the greater the voltage loss.
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.
NOTE: This procedure is harmless and highly recommended to maximize the reliability of your equipment, however if your heater is under warranty this may invalidate the heater warranty.
On some Kendrick Heaters, repeated tugging and flexing of the heater cable may cause the RCA plug connections to intermittently touch, causing a short circuit. 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 others. 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 can 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.  

If 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.
  • Do not make the power cord any longer than you need to because as the length increases so does the wiring resistance which translates into less voltage at your heaters and thus less heat. If you make the cord longer then use a larger a gauge wire to compensate for the increased wiring resistance, but 20 feet is about the limit for 12VDC power. Higher voltage power does not have this issue so it is preferable to run a long 120 VAC power cord to a battery charger or power supply located near the telescope so the 12VDC wiring is kept short.
  • A good wire to use is Low Voltage Landscape Lighting Cable which is available at your hardware store in gauges from #16 to #10 (lower # is larger wire). This cable is relatively inexpensive because it is only rated for 12 volts. The wire is larger than what you have on your DewBuster™ Controller which reduces the resistance in the wires.
  • 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 (use a Powerpole® connector or solder the wires for low resistance connections). The DewBuster™ Controller's power cord has ribs on the positive wire so I recommend using the Landscape Cable's ribbed wire as the positive.
  • 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, once again matching 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 cigarette plug power cord and you are connecting to a battery or other unfused power source, 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 (Heavy Duty power cords with cigarette plugs have an 8 Amp fuse in the cigarette plug since that is all that most cigarette sockets can handle,  however they still have an internal PTC 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 drops and surges 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. If you have any questions, e-mail me  for assistance.
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 Sensors to the telescope. Instead lay the Temperature Sensors on a surface or suspend them so they can acclimate to the ambient 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 start blinking and then 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. 
If you have any questions, e-mail me  for assistance.

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 this Cloudy Nights discussion.
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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