Fujitsu DL7400 Maintenance Manual page 153

[
Print head drive circuit control]
The controller (MB90706) reads print data from DRAM.
The data is set on the HDLSI print control circuit.
At this point, printing does not begin yet.
The MPU sets the excitation time (T1) and flyback absorption time (T2) in the HDLSI.
The MPU outputs print timing signal TIMER1.
In synchronization with print timing signal TIMER1, excitation signal PDV1-24 is output from the print head driver to turn on
the print head drive transistor (SMA4032).
After the specified excitation time has elapsed, the print head drive transistor is turned off and a flyback absorption signal
(FLYBK1-6) is output to activate the absorption circuit.
After the specified flyback absorption time has elapsed, the absorption circuit is turned off.
TIMER1
PDV1-24 (main excitation)
FLYBK1-6
(flyback control signal)
Head current
[Error detection circuit]
Detection of abnormal excitation
When the print head is excited, the head fire check circuit sends an excitation detection signal to the HDLSI.
If an unreasonable period elapses after the receipt of the detection signal, the HDLSI drives the PWSTOP
signal to stop +34 V.
It also notifies the MPU of the occurrence of the driver error.
T1
T2
Figure 5.3.20 Print head drive circuit
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