[sdiy] six-trak another problem!

[Robert Leiner]

Thanx,

I do have the service manual and two 2 channel scopes so i will have a look
were you suggested! (but i guess I just use on scope)

Soon again -
Robert Leiner

> There is a site on the net you can google to get the schematics.
> There is a 4174 for voice select, and each voice has a 4051 as an analog
> switch for the voice chip parameters.  Look at the output of that where it
> outputs to the SH cap and 3194 VCO input pin.  If that is flakey as you
> hear, then look at it and the input to the 4051 to see if it is flakey
> as well or stable.  If stable the 4051 is bad.  If nothing is flakey then
> maybe the 3194 is bad - swap with another voice's and see if the flakeyness
> changes to the new voice.  A 4 channel scope is wonderful working on this
> thing.
> 
> Barry
> 
> 
> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Bob Weigel
> Sent: Tuesday, May 10, 2005 12:41 PM
> To: Robert Leiner
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] six-trak another problem!
> 
> Ok, first of all, if it's octave jumping....there is no programming
> facility for that.  The six trak is only edited in coarse (half steps)
> and fine frequencies.  So it 'plays a couple octaves higher'...seems
> odd.  Or...does it?  Because hey..maybe it's banked out as high as it
> can go.  I seem to recall it sweeps from 0 to 48 which is 2 octaves up
> and down.  So...that could be what's going on for sure.  The unit is
> multi-timbral and I seem to recall that you can set each pitch
> individually on each oscillator..so....
> Look on the diagram and find the S+H cell that holds the data you
> are concerned with. Measure the output of the op amp buffer that feeds
> that circuitry witha  scope and you should be able to see the jitter.
> Now this is where it's nice to have dual trace scope.  But if you don't
> you can still manage to figure it out usually.   If you do then you can
> just hook one lead, having established that the problem is sometime
> before that op amp output test point, to the signal (with x10 selected
> if need be to reduce the probes effect on the signal..) common leg of
> the MUX chip.  Put the other one on the OUTPUT of the MUX chip going to
> the sample and hold cell for the octave function.  Now edit the
> function!  You will hopefully be able to see some correlation if you
> have triggered and set up the scope properly.....and quickly you'll see
> "ahh..there is the section of this garbled mess of data that is
> concerning me at the moment".   When you aren't moving the knob...does
> the signal still jump all over there?
> Anyway in the processor sweeps through all the functions of the
> machine in sequence so the idea is, if you trigger on one of them that
> is NOT jumping all around...the whole sequence should be laid out on the
> screen of your scope!  So trigger on the probe that is monitoring the
> common input of the mux.  If it is a consistent signal at the S+H cell
> but the output of the op amp is jumping all around...hmm..well try
> swapping the op amps or..check the solder on it.  Oh and "learn to fix"
> of course. :-)  That's always the best advice. Hehe.   -Bob
> 
> Robert Leiner wrote:
> 
>> Hello list members,
>> 
>> I have a problem with one of the voices on a Sequential six-track (voice
> 2),
>> it plays a couple of octaves higher and occasionally it's sounds like fast
>> random pitches.
>> 
>> I had a similar problem with my Oberheim OB-8 and after changing some
>> multiplexers the problem disepeared.
>> 
>> Any one have some advise on what it can be and where to start to look?
>> The multiplexer IC's are solered straight on the board so it's not as easy
>> to change as on the OB-8.
>> 
>> 
>> Any help is wellcome!
>> 
>> All The Best - 
>> Robert Leiner
>> 
>> http://www.leinermedia.com
>> 
>> 
>> 
>> 
>>