Crumar DS-2 Service Manual + Help

Hello there, I was wondering if anyone had a complete service manual for the Crumar DS-2 Synth out there. I have an incomplete 18 page version of the manual - missing several pages - which has made troubleshooting multiple problems with one on my bench difficult.

The Crumar powers up, and is putting out the right voltages from the power supply, but makes no sound and passes no audio at all through the external audio in jack.

Does anyone have any tips on where to start testing it? The lack of CV inputs has left my totally blank with ideas on how to test it, as the digital keybed could have issues as well.

Anyone with any insight, and documentation, please let me pick your brain !

Are these any good: