Teac MT-20D-IO - Page 29

3-3 Operation of tape drive system (PCBA Drive Control)
3-3-1 Servo circuit
Fig. 312 shows the block diagram of the servo circuit.
TPI9 RDY ---,
~--------~-----------------------------------E~
ENCODER
r -----, r----- --R43lr ---,M;--------..,
I II ~ II ~ I
IZV
I , , II ,
f::\ I ENCODER I I .... MONO- II'" F IV .-- MOTOR I POWER
~ ~----;"I --I PRE AMP I I TOR MULTI II _ ,~ DRIVE AMP I--T!-...,~I-{ TRANSISTOR
~L ___ ~I I I,
f---4TPZO
I II r- Tt- U I
I I START S-LIM
, , CONTROL , .---+---~...,
, HIS I I ~R. :~OR.
I RST I. I
HIS -----------:-i I M M
_
______________ :..,1 .f CLK '- .::::-.CLK I
~ I ~
I lOGIC TENSION I CRI CRZ
_ I LOGIC ~ CONTROL I I
: GO INT I 6 c~ t-i,---+--..J
I I DIRECTION FWD I CR8
LY~ _________ J CONTROL I' CR7
REV
FWD ----------------------------------;-~ I
GO-----------------~~ I
LOK----------------------------------~~ ~----------_;_I------------~~~T~Ma
LY~~&.9!L ______ J
Note: There is a model in which a fixed resistor is used as R43.
Fig. 312 Servo circuit block diagram
The servo circuit consists of an encoder preamplifier, comparator,
monostable multivibrator, F/V converter, motor drive amplifier, start
controller, tension contorller, direction controller, and logic circuit for
controlling the above.
The output signal ,from the encoder, which is turned in contact with the
tape, is amplified by the encoder amplifier, and converted into a pulse
signal by the following stage comparator. The monostable multivibrator is
triggered by the output pulse signal of the comparator, and its setting time
is set nearly to 1/2 of the encoder output signal period. Therefore, the
pulse duty of the output signal of the monostable multivibrator is approx.
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