OK, here is some information that promises to be useful:

Warning 72 and 73: In the unloading state, these warnings are caused
when reel motor rotation stops for ~2 seconds and there is no output of
reel frequency generator (FG) pulse. In the loading state, they are due
to no output of reel FG pulses while 14 capstan pulses are counted.
Warning 72 relates to no supply reel FG (Pin 33B of CN1 on the system
control board) while warning 73 relates to no take-up reel FG (Pin 34B
of CN1).

The corresponding Test Point (TP) voltages on Servo board 2 are TP7 for
the supply reel and TP9 for the take-up reel. Both should measure 6.00
VDC.

To check the power supply regulator board, here are the TP voltages
that should be present:
TP1: +11.7 +/- 0.3 VDC
TP2: +9.0 +/- 0.3 VDC
TP3: +5.1 +/- 0.2 VDC
TP4: +5.1 +/- 0.2 VDC
TP5: -14.0 +/- 1.0 VDC
TP6: +10.3 +/- 0.5 VDC
TP7: +16.5 +/- 1.0 VDC
TP8: +18.0 +/- 1.0 VDC
TP9: +12.0 +/- 0.4 VDC
TP10: +15.0 +/- 0.4 VDC

Are all these signals present at the proper level?