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Subject: RE: [chromapolaris] any advice on rebuilding the front panel needed .

From: "Paul D. DeRocco" <pderocco@...>
Date: 2007-05-09

> From: alex459686
> -what do the "SW" and "STB" signify on the PDF ? are these
> different types of switches ? -what kind of electronic parts
> / switches to i need ? are they on/off or merely a
> momentary style switch (not sure of the correct terminology
> here) .

The switches need to be momentary, normally-open, pushbutton switches. They
are arranged in a two-dimensional 8x8 matrix, each switch connecting one of
the STB (strobe) outputs from the circuitry to one of the SW (switch data)
inputs back to the circuitry. At any given instant, all the STB outputs are
floating except for one, which is grounded; and all the SW inputs are pulled
up to +5V through resistors. The STB output that is grounded selects a bank
of eight switches, and any of those that are pressed pull the corresponding
SW input to ground. The computer cycles through all eight banks at a rapid
rate. It's a standard multiplexing mechanism.

> -im assuming "J9A" , "J9B" , "J8A" and "J8B" are
> the connections on the PCB where the nasty
> fragile ribbon connectors would originally connect . which is
> which ? is this marked on the
> circuit board ? and are the connections counted from left to
> right / top to bottom or how ?

I don't have mine handy, but the connectors should have J numbers next to
them, and there should be some indication of which pin is 1, perhaps a dot
next to the pin, the digit 1, or maybe just a square PC pad for that pin
instead of the usual round or oval one.

> i guess it is then a matter of building a rats nest of wiring
> to connect the switches to each connection on the PCB .

It may look like a rat's nest, but it's really just an 8x8 matrix. The SW
lines on J8B just duplicate seven of the SW lines on J9B, so you can just
use J9B. Each SW line goes to (at most) eight switches, and each STB line
goes to (at most) eight switches.

> would i have to connect the switches "the correct way round"
> or do they connect either way round ?

Well, it's certainly essential that, for instance, the "Upper Function"
switch connect to SW1 and STB7, as opposed to STB1 and SW7, but it doesn't
matter which pin on the switch goes to which.


Ciao, Paul D. DeRocco
Paul mailto:pderocco@...