Buzzer Circuit - Olivetti ECR 7900 Service Manual

3-11. BUZZER CIRCUIT

The buzzer circuit uses as its input signal P74 from the CPU. This normally Low signal and goes
High on 2 conditions. First on an error tone, P74 goes Clocked until the error condition is cleared.
For a key beep tone, P74 goes High and then returns to its Low state. This pulse is of extremely
short duration.
Trouble shooting
- No buzzer sound when [clear] key is depressed.
Check the voltage at point (1)
DC +24V - - - Replace Main board.
0V - - - Check Power supply circuit. (P.9-11)
Y108540-8
R189
22K
(1)
B
BUZZER
ECR 7900 Service Manual
VDRW
R190
4.7K
BZ1
KPT-G1720-5V
Q13
DTC143EKA
35