[sdiy] roland rs202 vibrato speed mod + stuck note

[Tom Wiltshire]

 From what I can see on the schematic, the vibrato oscillator is at  
the bottom of page 5.
The part on the right-hand side from the gate input at (26) to the  
opto PH-1 is the vibrato delay circuit which looks like it uses the  
opto to control the depth of the modulation. The part on the left  
hand side must be the vibrato oscillator itself. But that doesn't  
look like a normal transistor astable circuit.
That said, we're still looking for timing capacitors if you wanted to  
add a 'range' switch, for instance. There aren't many caps in that  
circuit. VR9 looks a lot like a frequency trim, which would be a good  
place to start twiddling. After playing with the preset adjustment to  
see what it does, I'd experiment with the values of C13 and C14. If  
the twiddling works, you could also try replacing VR9 and the  
resistor R30 next to it with a 100K pot. If you've got a 'scope, have  
a look at the signal out of that vibrato osc at the emitter of Q5.

HTH,
Tom




On 16 Mar 2010, at 22:59, Travis Thatcher wrote:

> I just recently got a Roland RS202 string machine.  The thing sounds
> fantastic but there is one problem I'm currently trying to diagnose.
> id  on the strings II setting, the 2nd to last c is stuck on. the
> other notes work, but it will not turn off. All the rest of the keys
> work fine, and all the other voices work as expected.
>
> I'm also curious as to the possibility of adding a vibrato speed mod.
> I know there is a vibrato osc circuit, looking at the following
> schematics, but I'm afraid my circuit knowledge is limited enough and
> I'm not sure what would need to be variable to vary the osc. speed.
> Got the schematics from here:http://www.loscha.com/scans/
>
> Any help would be greatly appreciated.
>
> -Travis
>
> -- 
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