Printhead Drive Circuit - OKIDATA Pacemark 3410 Service Manual

Page: 18
Service Guide PM3410
Chapter 2 Principles of Operation

2.1.05 Printhead Drive Circuit

This circuit is used to drive the 9 print wires. The signals HD01 through HD09 from Q2 are used to enable
the individual wire drivers (TRA1 and TRA2). TRA1 drives Pins 1, 2, 6 and 7. TRA2 drives Pins 3, 4, 8 and
9. TR7 drives Pin 5. The HD ON signal enables the drive circuit when printing is desired. The head drive
duration is determined by an RC integrating circuit which modifies the HD ON pulsewidth. The pulsewidth
of the HD ON signal varies with the number of pins being driven. The drive time is increased as a greater
number of pins are driven, but decreased as less pins are to be driven. The drive time is also increased if
the head gap lever in placed in positions 3 through 9. The RC circuit is also used to compensate for the
fluctuation of drive voltage (+38vdc).
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