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LX200 Keypad -- Plugging it Hot (turned on)

I suggest great caution in doing this.  I would in fact go so far as to say "DO NOT PLUG OR UNPLUG THE KEYPAD WHILE THE SYSTEM IS TURNED ON!!!"

Here are the reasons.  Because of the design of the power supply in the keypad and the fact that two digital signals are also transmitted through the connecting cable, there is a distinct probability that hot plugging might destroy the receive chips in both the keypad and the computer main board.

The problem is that the full power supply voltage of 12 to 18 volts is connected through the cable.  The plug is not the correct type for hot plugging.  A hot plug must have a ground connector (pin) which makes connection before any other connections are made. The telephone type plug is not of this type.

What can happen is that the power line might be connected momentarily before the ground. This momentarily applies, through the electronics, the full supply voltage to the input and output terminals of the send/receive chips in both the keypad and the computer board.  These chips are designed to operate and do operate at a 5 volt maximum level. In this instant, the chips could burn out. There is also the possibility of static electricity discharges taking place when the cable is plugged in at either end.

I believe that the system was designed to be turned on and off only with all connections in place.  Meade gives this warning. This may or may not be a good design decision, but it is a fact. (I think it not good)

Also, if for some reason the keypad cable looses its ground, the same result may be effected.  My personal feeling is that the modular connector is not the best choice for this application.

As an aside, I might note that many pieces of equipment have this same problem.  When hot connection is desired, an appropriate plug with a good first on, last off ground must be used. All cables carrying power voltages should have this type of plug.  In 40 years of consultation on electronics problems I would estimate that half the problems relate directly to power supplies and improper grounding.

Summary:  Do not hot plug your LX200 equipment.

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