Vintage Synth Repair

Hi group.
I'm searching for a pdf file of the service manual for the roland JX-8p.
My JX-8p has the following problem:
- When I select a program which uses a square wave and an envelope with 
fast attack (piano like) some of the notes sound weaker than others, 
but in an alleatory way from patch to patch.
This also happens when notes are played from an external keyboard thru 
MIDI IN.

Any suggestions?

Best regards and merry christmas to you all!
José
Portugal

Hi,

does this really happen randomly, or something like every time you played
something like 6 or 8 notes (whatever the notes...) ?

A demultiplexer (surelly a CD4051, or something similar) could be faulty, the
only thing one wouldn't understand is why would it happen only with square
waves... ! If it really does, and your demux / s&h circuits are fine, then I
think it could also come from the adress/data bus, as the DCO and dacs used to
generate the enveloppes should share the same bus.

Look at the MKS-70 schematics, as it seems to basically be two JX-8P in a rack.

Michel

> Hi group.
> I'm searching for a pdf file of the service manual for the roland JX-8p.
> My JX-8p has the following problem:
> - When I select a program which uses a square wave and an envelope with
> fast attack (piano like) some of the notes sound weaker than others,
> but in an alleatory way from patch to patch.
> This also happens when notes are played from an external keyboard thru
> MIDI IN.
>
> Any suggestions?
>
> Best regards and merry christmas to you all!
> Jos\ufffd
> Portugal
>
>