Alarm Circuit - Oki ML420 Maintenance Manual

2.1.8 Alarm Circuit

(1) AC fuse open alarm
(a) 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 ALM-N signal to turn on the Thyristor.
This cause the secondary coil (50V) of the transformer to be short-circuited, causing
an overcurrent to flow through the primary coil and making the AC fuse (transformer
assy) open.
(b) Overvoltage detection
50V, 12V and 5V voltages are monitored, at overvoltage alarm circuit turn-on, the ALM-
N signal is transmitted to the thyristor, then the AC fuse (transformer assy) opens.
(2) Alarm processing when DC power is low.
50V is converted into the POWLEV signal (0V to 5V) by R542 and R541 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 µ sec. to control and maintain the
impact necessary for each printing pin at the fixed value.
(b) Print speed
(3) FAN alarm
The MPU detects 5V on the FANALM signal even through the fan is driven.
42113901TH01 Rev.3
50V
R542
R541
Voltage, 50V Pass number
38V or more 1 Pass
25V to 37V 1 Pass
25V or less 1 Pass
5V
R512
POWLEV
Print speed
100%
100~30%
30%
FANALM-P
Oki Data CONFIDENTIAL
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