[sdiy] OT micromoog keyboard & mono/poly filter problems

[DCMagnuson at aol.com]

In a message dated 6/7/01 4:25:43 PM Eastern Daylight Time, Mesa237 at aol.com 
writes:

> Also try cleaning key contacts.  i believe it was a bus bar type mechanism; 
>  though it
>  is unlikely that all notes would be affected if some of the surface area 
was 
> 
>  dirty.  i would look at some of the opamps in the keyboard cuicit; they 
are 
>  more likely to go out than the discrete components around them.  just an 
>  idea, though.
>  
>  i think i have the schematics somewhere around my apartment; i'll try to 
> find 
>  them tonight and give more specific advice.


I think this may be part of the problem as well.  I'm currently building a 
monosynth with a keyboard assembly salvaged from an old organ.  After 
soldering the the resistor ladder across the keyboard contacts I've noticed 
that the resistance is incorrect on certain keys.... sometimes off by 50-75 
ohms (and I used 100 ohm 1% resistors on the ladder).

This could very well be the same problem with your synth.  If it's possible, 
disconnect the keyboard from the circuitry and test each key's resistance 
when pressed... it should be rather obvious if theres a problem.  

My only problem is trying to get the bus bar out of the keyboard without 
upsetting all of the j-wires...  this particular keyboard assembly is not 
easy to dismantle.

Dave Magnuson