Citizen CLP-621, Technical Manual

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2-2. Operation of Control Parts
2-31
CLP-621 & CLP-631
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.
+5V
IC1
CPU
R77
R
A
R: Resistance of a thermal element
TR2
Thermal head
R83
HEADRES
ANI5
10
+3.3V
(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
BUZZER
+24V
[Main PCB]
P77
171
D11
R121
R118
DTR4
DTC143EUA
P225
R120
P226
BZ1