Citizen CL-S400DT Technical Manual page 35

Chapter 2 Operating Principles
2-2. Operation of Control Parts
Thermal resistance check:
When the printer is turned ON, the thermal resistance check is conducted. If any fault is found,
the POWER LED blinks in red and the LCD displays "Alarm Head Check".
During the thermal resistance check, pin 15 (nHCVON) of the FPGA (U11)) goes "Low", and
Q1 turns ON. Thus, +3.3V is supplied to the "SA2 Head", instead of +24V.
The following figure shows a simplified circuitry under thermal element checking, where Q1
turns ON and a thermal element "R" is selected. The voltage at point "A" becomes the value
divided by R60 and R. The CPU monitors this voltage at pin 10 (HDRES), and check if the
voltage is in an allowable range or not. (If R is disconnected, the voltage at point "A" will be
abnormal value: about +3.3V.)
Every thermal element is successively checked in this way.
+3.3V
A
R: Resistance of a thermal element
(3) Buzzer driver
This circuit drives the buzzer.
To sound the buzzer, the CPU outputs a pulse from pin 171 (BUZZER). The transistor Q24
turns ON and OFF, and the buzzer sounds.
U1A
CPU
171
P77
[SA Main PCB]
CL-S400DT
Q1
R60
R61
HDRES 10
R
SA2 Head
BUZZER
U1A
CPU
ANI5
+24V
BZ1
R128
Q24
DTC114EM
2-22