I reported a while back that I had had a dec failure, which I isolated to
to the keypad. In diagnosing the problem, I came up with some interesting
observations (so to speak).

The keypad S key stopped working, so I traced things out to see what
specifically had failed. The keypad is wired to provide a separate
contact closure for each button, not the more common x-y matrix.

The individual buttons feed two 74HC166 8-bit parallel-to-serial converters.
These convert the keypad button state to a serial bitstream that is then
read by the keypad's microcontroller (a masked-rom something-or-other, the
number is covered up. I'd guess something in the Motorola 65xx line).

The microcontroller uses this info to send an 8-bit character to the
scope whenever a key is pressed OR released. The keypad-scope communication
appears to be standard 9600 baud 8 bit data, 1 start bit, 1 stop bit.

The scope sends characters back to the keypad to be displayed, or to
change the state of the various led's.

The problem with my keypad is that one of the 74HC166's died. This shouldn't
be a common problem; I checked the chip's supply voltage and it's well
within tolerance, so it was most likely a random failure.

However, the LX200 design is showing its age... the 74166 is considered
obsolete by many chip makers, although it's still available.

Now a word of praise for Meade's outstanding customer service.
I decided to call them before I fixed the keypad myself to see what they
had to say. My scope's out of warranty, although it's only 18 months old.

Meade is sending me a new keypad, free of charge, immediately, before I
even send the old one back.

This is my first encounter with Meade support, and I don't see how it could
be any better. (Well, I suppose they could FedEx early morning delivery)

One final tidbit.. the main processor in the scope is a Motorola 68000;
an old and venerable processor. Should Meade be criticized for using such a
slow, old, CPU?

For those of you in the East, whenever you buy something at CircuitCity,
*every* point-of-sale terminal in the store is run by their proprietary
in-store system, which they call a CC-130. Each CC-130 runs at least 16 POS
terminals, handles a satellite link back to the home office, runs the
ticket printers, and does a bunch of other stuff.

This machine's CPU is, you gessed it, a Motorola 680x0!
(Specifically, a 16Mhz 68020)

Controlling a scope must really be something, no?
_______________________
| Bill Ezell |
| www.quackers.net |
-----------------------
The box said 'Win95, NT, or better', so I used Linux

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