Rice Lake Okidata 320-390-420 Turbo - Service Guide - Manual (Page 25)

Page: 11
Service Guide ML320/321Turbo
Chapter 2 Operation Description
2.1.8 Alarm Circuit
(1) Head drive time alarm circuit
This circuit monitors the drive time using the HDALM signal interlocked with the overdrive signal of each
drive circuit.
If the drive time of any drive circuit exceeds the specified time, the drive fault alarm circuit sends an
ALARM-N signal to turn on the SCR (SO).
This causes the secondary coil (40V) of the transformer to short-circuit, causing an overcurrent to flow
through the primary coil and open the AC fuse (transformer assy).
(2) Alarm processing when DC power is low.
+ 40V is converted into the POWLEV signal (0V to +5V) by R28 and R29 and input into the A/D port of the
MPU to control the drive time and the print speed (pass number) of the head.
(a) Head drive time
The head drive time is lengthened to compensate for the amount of voltage drop by monitoring the
POWLEV signal once every 500 m sec. to control and maintain the impact necessary for each printing pin
at the fixed value.
(b) Print Speed
(3) Head overheat alarm
The voltage of the output TSD signal of the thermistors, one of which is in the printhead and the other in
the printhead driver, is monitored by the CPU/AD port to control the voltage