[sdiy] Adapting organ keyboards for synth

[David G. Dixon]

Hello all!

First, let me apologize for stirring the pot yesterday about roll-yer-own
pcbs.  It was a slow news day, and I was looking for some excitement!

I spent a goodly portion of Saturday tearing apart a very dusty and
neglected Farfisa Silver 404 electronic organ for parts, and managed to
salvage, inter alia, two very nice 44-key keyboards and a 1-octave
pedalboard.  These are on sheetmetal substrates, with pcbs containing only
diodes and pin connectors.  They appear to be set up for a matrix circuit
organized by octaves rather than the (standard?) 8 x 8 format.

At this point I'm only interested in a basic gate/trigger and CV-generating
application, and I'd rather not have to redo the pcbs if I can avoid it.
Hence, can anyone here tell me where I might go to get some insight into how
to build a 12 x 4 matrix scanner for these little beasties, preferably
without programmable chips?  I must confess that this is one part of synth
circuitry which interests me very little (for now), and I just want to "plug
and play" something reasonably quickly (although I'm apparently willing to
waste three weeks of my life thinking about 4-pole filters!).  Is there a
ready-made circuit concept lurking somewhere on the "internets", perhaps?

I can tell you that the keyboards were connected to a board with 3 74LS173Ns
(4-bit D-type registers with 3-state outputs), 1 74LS245N (octal bus
transceiver), 1 TMS2732 (32Kbit (4Kx8) MOS 3-state UV-Erasable EPROM), and 1
DN7406N (TTL Hex Inverter Buffer/Driver, I think).  Obviously, the EPROM is
critical, and I'm not going to try reverse-engineering that.  

Any help most sincerely appreciated!

Dave Dixon