Radio Shack TRS-80 PT-210 Service Manual page 11

Keyboard Unit
Â
When a key that corresponds to the data to be input is pressed, its contact operates and a signal is sent
to the control unit.
Printer Unit
The printer unit is controlled by the control unit. It prints data to be transmitted and receives data on ther-
mosensitive paper (in roll). In the OFF-LINE mode, the printer can be used as an ordinary typewriter.
CR motor assembly
The CR motor controls movement of the thermal head. When a control signal is input to the CR motor,
the motion of the motor is transmitted to the head assembly@ fixed by the CR timing belt
(2)
through
the motor timing pulley
(l)
on the motor shaft.
Assembly
Figure 7.
The motor causes the thermal head
(A)
to move, in the direction of X-axis, a distance that corresponds
to the size of one character, and to do so within 6 pulses of the motor control signal. Therefore, its
moving distance is 2.54 rnrn (1
/lo'').
The motor reverses when the head has travelled the distance of 203.2 mm, which is the effective
travel of the thermal head good for 80 characters, and the head assembly
(3)
is caused to return to the
start point. The start point is determined by the photo interrupter assembly
(5)
While the thermal head
is returning to the start position, it is not in contact with the thermosensitive paper because of the op-
eration of a relief solenoid.