[sdiy] Matrix 1000 repair, unexpected hack

David Brown davebr at earthlink.net
Tue May 1 06:14:09 CEST 2007

Pin 14 of U808 is also 'pulse'.  U808 is an interrupt timer.  One 
'guess' might be the unconnected wire went to pin 24 of U809 at one 
time.  If pad 24 is ground, perhaps this was a PCB layout error and 
hence the lifted pin and wire.  Why it is cut, though, is still a 
mystery.  'mute' is just a general purpose output pin from a latch on 
the processor.

I might have it backwards, but doesn't CTS-0 need to be grounded for 
MIDI out to work?  MIDI output for the M-1000 is used for dumping 
patches and group mode so you wouldn't notice it for general usage.

Have you tried a  re-initialization? (power up with enter button pressed)

I might also try a calibration? (Ext Fn 7 enter, select test 0 enter)


At 05:53 PM 4/30/2007, David Brown wrote:
>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.
>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).
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