Hallo ! Trying to help an on old friend with his model D , The upper oscillator,
oscillator 1 have , as you know , six different settings on its switch. The three
to the left , the triangel shapes work , even if the sound is weak . But the three squaresounds at the right doesn´t sound at all . ( the other osc. 2 and 3 work) . I have changed all four ICs 741 on the large card but no luck.
The unit has new electrolythic caps all over both on the powerside and on the circuitboards . Thanks for help . Haven´t studied the schematics yet .
That you should do. When I serviced unknown synthesizers I started at the saw core tracing the signal within the circuit to the output.
So if the square shaper creates the outputs, there might be a mechanical problem within the switch as well.
A weak sound is a problem as well. And again it might be an electronical or mechanical reason.
So I would compare the ins and outs of each circuit stage with a scope until you find the problematic location. Just to replace some components an advance is ok, but does not solve the problem.
Hope that helps…
I have tried to change the 7 IC741 ones but no luck . Osc. number 1 only produces the triangle sounds not the square ones. I have resistancemeasured the switches and compared them to each other but cant find any differences between them . Another tech said I might be forced to take apart the upper switch and carefully clean it inside. Dont know if it will help just because there is no difference between them when I measure with ohmmeter. On the oscillatorcard there are two other ICs . Is it any meaning to change them ?
You should check the signal passing the switch with a scope additionally to the resistance measurement. If the switch lets the missing signal pass, continue with the next processing stage, again with a scope and a running oscillator.