Operating instructions

8. Put the machine into Fast Forward or Rewind and adjust VR1 FAST
SPEED on the I/O CONTROL PCB Assembly (front panel) to obtain a
frequency reading of 64 kHz.
NOTE: If VR1 is left fully clockwise, a time delay will occur when going from
fast wind modes to other modes of operation.
9. Wind the tape until there is an equal amount of tape on the Supply and
Take-up reels. Check the Fast Forward and Rewind frequencies. They
should be no more than 500 Hz apart. If there is a difference of more
than 500 Hz, extend the CAPSTAN CONTROL PCB Assembly and adjust
VR5 for equal Fast Forward and Rewind speeds.
10. Verify that the frequencies observed during Steps 7 and 8 are still
correct as some interaction of the trimmers may have occurred.
Turn VR2 on the REEL SIZE DETECTION PCB Assembly
counterclockwise to find the point where the frequencies start
decreasing. Then turn VR2 clockwise 180 degrees from that point.
11. Remove the Extension PCB Assembly and reinstall the CAPSTAN
CONTROL PCB Assembly. Thread the machine with a tape containing a
pre-recorded 1 kHz sine wave. With the tape at the beginning of the reel
(heads) put the machine into Play mode.
12. Using an oscilloscope, monitor the XLR line outputs and check the time
required for the tape to reach play speed (i.e., for the signal on the scope
to reach 1 kHz). To reach 15 ips should take 0.5 seconds, to reach 30
ips, 0.8 seconds. If the tape is not getting up to speed in the appropriate
time, adjust the Play Gain VR1 (front panel of the CAPSTAN CONTROL
PCB Assembly) clockwise. If the tape is overshooting the speed, turn
the VR1 trimmer counterclockwise to minimize the overshoot. Return to
the beginning of the reel to confirm start-up and overshoot specification.
13. While still in Play mode adjust VR2 PLAY DAMP (front panel of
CAPSTAN CONTROL PCB Assembly) counterclockwise until the tension
arms start showing instability, then turn VR2 clockwise until the tension
arms stabilize. Once stability is achieved continue turning the trimmer
clockwise 2 more full rotations.
Figure 6-12
CAPSTAN CONTROL PCB Assembly
VR1 PLAY GAIN
VR2 PLAY DAMP
TP1
VR5
VR3 FAST GAIN
VR4 FAST DAMP
VR6
TP3
GND
TP10
TP9
Section 6 Alignment
6 - 18
October 1990
MTR-90III Operation and Maintenance Manual