Radio Technique
George M. Myers
SOMETIMES YOUR RADIO starts acting peculiarly, servos slow down or get twitchy, range goes to nothing, controls start affecting one another, and so on through a long series of bewilderments. What to do about it?
Remember a while back when I stated that this isn't a technician's column? That's still true. But you don't have to be a technician to use your head! First try isolating the system from outside interferences. Take the radio system out of the plane and string it out on a wooden table. Now turn everything on and work the sticks to see if the problem has gone away. If it has, you have a clue about what to do next.
The arrangement of servo wires within your airplane can have a significant effect on the system, regardless of how much you paid for it. Many times all that is necessary for good performance is a careful rearrangement of the equipment to keep servo leads, wire pushrods, landing gear and other bits of metal away from the receiver antenna. Try it, the price is right. When making an installation for the first time it's good practice to put the battery forward, the servos in the middle, and the receiver in the rear with the antenna as far from system wiring as possible.
Let's pretend that stringing out the airborne set didn't help. Consider, does the problem appear only when a certain control is moved? If this is the case, the servo may have a dirty potentiometer, or damaged gears, or a noisy motor. Exchanging servos will help you to decide if the servo is the culprit. If it is, you may decide to open it up for investigation. Assuming that you have no service manual, it would be a good idea to sketch the parts you remove, and to identify them with bits of tape or grease pencil marks, so you can get them back together correctly. Slip the motor out of place (it may be glued in) or remove the gear to let it run free. Now turn on the set and displace the control to that servo. The motor should run continuously in one direction, and if it's at fault, the trouble will return.
Assuming the motor isn't at fault, move the shaft which drives the servo output wheel, which is also connected to the servo potentiometer in most cases. If the potentiometer is dirty, you'll know it. Most often, all that is needed is to wipe it clean with a piece of tissue, lubricate the track and reassemble the servo.
Still haven't found the trouble? Push gently on all of the components on the amplifier board, using a dowel or balsa stick. You may find a loose component or wire. Solder it back in place with 60/40 rosin-core solder and a 1/8" diameter pencil-point tipped soldering iron rated at 27 watts or less.
Let's say that the servos are OK. Try measuring the battery voltage at one of the servo plugs. It should read about 4.8 to 5.2 volts, and shouldn't drop more than 1/10th of a volt when the servos are moving. A bigger change is grounds for suspecting a broken wire or defective battery pack. Measure the voltage at the plug from the pack. If the voltage drop is less when the servos are moving than it was previously, go looking for that broken wire. The most likely places are next to the plugs, and any place where a wire exits from a case. Tug lightly on each wire in turn. If one comes apart in your hand, you've got your culprit. Examine the switch harness carefully, because it takes a lot of abuse. Work the switch a few times to see if it's dirty. If so, a spray of TV tuner cleaner may help. The same treatment is good for dirty plugs, which can be pretty noisy.
Still no answer? Try recharging the system before you do anything else. The charger may not be doing its job. After a full charge your battery pack should read about 5.8 volts. A reading of 5.4 volts or less is good grounds for suspecting the charger. Now before rushing off to junk the charger give a little consideration to the wall socket it's plugged into. The charger probably is designed to work on 115 volts A.C. Put less in and you get less out. If the lights in your house, or a light plugged into that socket, seems dimmer than your neighbor's, you may have a problem in the house wiring.
All that's left is the receiver, and if you're not a technician let the manufacturer fix it. You may have a cracked crystal, loose elements in the IF cans, a cracked circuit board, or other troubles. If you're not equipped to fix these things you'll just make them worse.
We haven't said anything about the transmitter. The best way to differentiate between transmitter and receiver problems is to test with someone else's transmitter. Another manufacturer's transmitter on your frequency will work your system just fine, with a few rare exceptions. You might have a noisy potentiometer on one of the control sticks. Unless you have a General Class FCC Radio Operator's License leave it alone. Let the manufacturer's Service Center take care of it.
In some cases, particularly where persistent overcharging of the battery pack has taken place, the electrolyte is driven out of the cells. This leads to an increase in the internal resistance of the cells. If the cells, when the radio is operating, show a new battery pack, you may be able to solder in a replacement cell or two without damaging the pack, but you should consider that most packs these days are potted to resist vibration, and this makes the job more trouble than it's worth. A battery pack is usually cheaper than a new plane, right?
Thanks go to Wally Zober of the Suffolk, NY Falcons for suggesting the theme of this column.
(My address is 70 Froehlich Farm Rd., Hicksville, NY 11801.)
Transcribed from original scans by AI. Minor OCR errors may remain.
