The most common problems involve power. Some units are operated from the internal battery, others run on aircraft power, some pilots use both. With few exceptions, if the power is OK, the unit will function properly.
So what can go wrong with the power? Well, first let's consider the internal battery. It is a sealed lead-acid battery, so the chemistry is very similar to a car or aircraft battery. The worst thing that can happen is to discharge it completely and leave it that way. This can happen if the unit is left on, for example. That is why there is a battery switch on the rear panel. If the battery switch is off, then the battery is completely disconnected. (Good for long term storage, for example.)
It's not a good idea to discharge the battery completely, and if the battery is discharged repeatedly it will be ruined. It's the same with a plane or car battery. Don't take it all the way down. And when it is used, recharge it as soon as practical. (Not next spring!)
Remember, the battery switch disconnects the battery. If the switch is off, you cannot charge or use the battery. But the rear switch is not the power switch. The power switch is on the front panel. Sometimes pilots turn on the front switch, don't see anything, and then remember to turn on the battery. This isn't the proper sequence. Here's why: When the Altitude Alerter is turned on, it's computer "boots up". This is a start-up sequence that sets a number of variables to the proper value. It happens when you flip the front panel power switch on. If there is no power (because the battery switch is off) then the boot sequence cannot occur. The answer: Be sure the battery switch is on first, then turn on the front power switch.
That leads us to the next major problem area, aircraft power. If the battery switch is on, then any momentary interruption of power from the aircraft is not a problem, because the battery will carry the load during the power glitch. But if the battery is not in use, then a momentary interruption is the same as the previous paragraph, with the possibility of an incorrect re-boot. The computer chip has a built-in "watchdog" function that usually catches these problems, but occasionally a power interruption can result in a blank display, or other difficulties.
Where do these interruptions come from? Usually the cigarette lighter is the culprit. It wasn't designed to be a power source, it was designed to light cigarettes. A little corrosion can cause a wide range of problems. If your alerter seems to go blank at odd times, or has other strange symptoms, suspect the power source.
Our cigarette lighter cords are fused. The fuse is located in the center pin of the large plug. To change the fuse, press the pin in, turn it counter-clockwise about 45 degrees, and pull it out. The fuse can now be removed. It should be a 3 amp fast-blow fuse, type 3AG. This is a common, widely available fuse.
If the display goes blank, here's what to do. Turn the unit off on the front. Also turn the battery switch off on the back, and unplug the power cord if you are using one. Now wait for at least three minutes, this is necessary to allow the internal circuits to discharge. Then turn on the battery switch on the rear panel, and finally turn on the front power switch. The sequence is important, the last thing to turn on is the front switch.
If that doesn't fix it, call us!
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