b. Check the specific model of recorder and its maintenance manual to
determine if the tachometer (tach) signal is 64Hz, 32Hz, 16Hz or other frequency.
You should also determine the mode of operation, because in the record/record
standby mode, you have a vertical sync input which also controls the servo
frequency.
c. In the playback mode, you have a delayed type of control track input which
determines the servo frequency.
d. Also during play/standby you have a 60Hz signal from the power supply.
e. The servo frequency is a combination of two or more frequencies (fig 1-8).
Either or both may be variable, and this combination of frequencies is used to
control the speed of the head drum motor.
Figure 1-8.
Block diagram of servo signal source
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