Radio Shack TRS-80 PT-210 Service Manual page 31

Head Release Solenoid
The solenoid releases the head from the platen when:
0
The carriage is returning.
0
The PAPER ADV key is kept pressed.
1 1
I/O Port
8243
f7t
Jr
MGND
Figure 22.
VMM +7.5V, which is commonly used for the carriage return motor and the line feed motor, is also
used as the power supply for driving the solenoid. When P70 becomes low, the transistor turns on and
the solenoid is activated.