Denon DP-1200 Motor Won't Turn

I'm troubleshooting a Denon DP-1200 that won't start. It turns on and haven't found any obvious problems. I was hooking up the scope to test, then the motor started turning when I hooked "ground" up to the scope's ground. So it works when circuit ground is connected to earth ground. This must tell me something very important but I'm still not sure what the issue is. The schematic below shows what I was using as circuit ground.

Full service manual can be found on vinylengine.
 

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