If one waveform is being produced, they all are being produced. The only possibility is that they are not getting from the 3340 to the TL074, or from the TL074 to the output jacks. Use a scope or an audio probe to verify the signals are on 3340 pins 4 and 10, then see if they get to TL074 pins 3 and 12. If so verify they are on pins 1 and 14, then see if they get to the jacks board pin header/socket and from there to the jacks. Where they disappear is where you need to fix a couple solder joints.