...
The unit makes a terrible sound while moving the tape, so clearly something is still amiss…
Time to get the oscilloscope. I put the yellow probe on U27 pin 3 which should be a tacho signal. The blue probe goes on U21 pin1+2 which is the SFD signal (Servo Fail Detect). Switching on then shows the following (the tape is accessed at startup and does its scream):
...
That does look like there is no tacho at all. Next step is to check tacho in at U26 which is an 1820-1048, translating to the N8T20N, a monostable multivibrator. Pin 6 (not marked on the schematic but that is the - input) should contain the ATC Analog Tach signal; let’s put that on yellow now:
...
That at least shows as something 
Enlarging that signal shows:
...
58kHz!? It does seem a real signal from the wheel because when the motor seems to stop we see it slowing down:
...
And it does the same at the start:
...