[sdiy] U-20 questions

[Bob Weigel]

Oh duh yeah the notes always think they are being held probably :-).  
That would do it maybe. Possibly there are some that are just stuck down 
or a diode shorted or something... If it thinks keys are being held from 
the time it boots it will never retrigger those notes until the key is 
released maybe. Hmm. 
    And yes Roland has been GREAT along with Kawai at keeping up on old 
parts.  I really appreciate both of those companies for going the extra 
mile in that respect. -Bob

Paul D Brooks wrote:

>--- Bob Weigel <sounddoctorin at imt.net> wrote:
>
>  
>
>>That seems unusual.  Hmm.  U-20 is a rompler. In
>>some designs I can <cut>That's a strange one.   -Bob
>>    
>>
> Tony Kalomiris wrote:
>  
>
>>>Only some notes in each octave (I forget which)
>>>      
>>>
>>work.I removed every <cut again, for everyone's
>>    
>>
>pleasure>
>
>Ah, yes... the problem is almost certainly related to
>the bottom part of the key contact system (if the
>upper contacts have been cleaned properly)... not only
>are the circuit traces part of the ribbon-like part on
>the bottom, but there are some surface mount
>components in there as well.  likely, the key scanning
>diodes, iirc.
>
>Hence, one of the key scan lines is out, so the
>problem repeats itself.
>
>Of course, this does not show up on the schematics...
>the topology is there, but nothing to tell you how to
>fix embedded circuit traces or diodes inside a flat
>ribbon style plastic assembly. 
>
>Roland is, of course, the only supplier with such an
>assembly in stock (besides perhaps a few repair shops
>willing to play ball).  They used this type of keybed
>in plenty of synths in that era, and hopefully will
>have some in stock... they are better than most in
>this respect.
>
>-paul
>
>
>  
>