Vintage Synth Repair

I have had a polysix that I've been wanting to restore or at least repair to a working state again. The power wire has been replaced and I'm not sure its correctly connected, so I guess I'll start there! When I plug the synth in it just hums constantly unless I switch the tape output switch then the hum gets softer. All the lights are on and I'm not sure if this is correct or if a power problem is causing this. The speed knob seems to be working but nothing else as far as sound or knobs. Anybody have any ideas where to start? 

Thanks, TheCat