Buzzer Driver - Citizen CLP-621 Technical Manual

Thermal resistance check:
When the printer is turned ON, the thermal resistance check is conducted. If any fault is
found, it is memorized and, when the printer is turned ON next time, the CONDITION LED
and ERROR LED alternately blink on the operation panel.
During the thermal resistance check, pin 117 (HCVON) of IC11 (Custom IC) goes to "High"
level, and DTR2 and TR2 turn ON. Thus, +5V is supplied to the thermal head, instead of
+24V.
The following is a simplified circuitry under checking, where TR2 turns ON and a thermal
element "R" is selected. At the point "A", the voltage divided by R77 and R is developed.
The CPU monitors this voltage at pin 10 (HEADRES), and check if the voltage is out of the
allowable range or not. (For example, if R is open, the voltage at point "A" will be about
+3.3V.)
Each thermal element is successively checked in this way.
R: Resistance of a thermal element

(4-4) Buzzer driver

This circuit drives the buzzer.
To sound the buzzer, the CPU outputs a pulse from pin 171 (BUZZER). The transistor
DTR4 turns ON and OFF, and the buzzer is driven.
IC1
CPU
171
P77
[Main PCB]
+5V
TR2
+3.3V
R77
A
R83
HEADRES
R
Thermal head
+24V
R118
R120
P226
BUZZER
2-31
IC1
CPU
10
ANI5
R121
D11
BZ1
P225
DTR4
DTC143EUA
2-2. Operation of Control Parts
CLP-621 & CLP-631