[sdiy] Matrix 1000 repair, unexpected hack

[David Brown]

On my schematics CTS is tied to 'pulse' which is derived from an 
analog mux summing all of the voice outputs. It looks like the mux is 
controlled by a 'mute'.  There is a comparator in there looking at 
the audio levels. I don't understand it at all but would venture a 
guess that it is part of some type of calibration or self-test where 
they want to inhibit transmission of MIDI.  Why, I don't know, but 
with the circuitry, CTS is disabled when there is audio output so I'd 
guess you'd never see it in 'normal' operation.

Interesting, though.  Does the Matrix-1000 do real-time 
calibration?  I didn't think so since the oscillators are digital.

Dave



At 11:54 PM 4/29/2007, Andre Majorel wrote:
>On 2007-04-29 23:26 +0200, . wrote:
>
> > After opening [a Matrix 1000], i stumbled across a weird thing,
> > pin24 (Clear to Send) of the 68b50 ACIA (IC U809) is
> > purposefully unsoldered and left unconnected (by human
> > intervention) and the timer(UM82C54) U808 just aside it has a
> > wire directly solderd on pin 14 (Gate 1). The wire is cut at 2
> > centimeters and left unconnected too.
> >
> > Theses 2 chips, U808 and U809, are involved in MIDI handling but
> > so far MIDI IN and OUT seem to work OK, should i worry about the
> > CTS not connected ?
>
>I'm not familiar with the 6850 but CTS is a hardware handshaking
>signal and as such does not apply to MIDI. If there's an internal
>pull-up, you can leave CTS unconnected (or so I expect).