In the early history of dot-matrix printers, there were
several wires in the Centronics parallel port that were
supposed to indicate different fault conditions to the PC.
The PC software usually messed up and translated all these
fault conditions into one condition called "paper out."
Even today, when PC DOS detects a problem with the printer,
it assumes that you have run out of paper. This topic is
explored more thoroughly other sections.
There also is a paper-out switch in the printer. Early
dot-matrix printer manufacturers wanted to make certain
that the print head did not print without paper, and therefore,
ruin the platen. Unfortunately, the paper-out switch is
located early in the paper path perhaps three inches before
the print head. This means that the printer will think it
is out of paper while the print head is printing a line
three inches from the bottom of the page. In effect, there
is no way to print in the bottom three inches of the last
page to go through the printer. The only solution is to
disable the paper-out switch.
If you manually insert a page, chances are the printer
will think that it is out of paper prematurely, because
it cannot print on the bottom three inches of a page. Try
disabling the paper-out switch.
Printing on the platen causes the rubber of the platen to
harden. This reduces the capability to make good-looking
characters and to grab paper. In addition, it makes the
platen dirty, smearing ink on the backs of papers. Later,
when the paper is stacked, the ink comes off the back and
smudges the front.
You can disable the paper-out switch by doing one of four
things:
* Adjusting the software. This is the preferable method.
Some printers can ignore their paper-out switches if the
proper command is sent to them by PC software.
* Adjusting the dip switch inside the printer See your
printer's manual.
* Adjusting the paper-out switch. Locate the paper-out
switch by pulling strips of paper through the paper feed
path. Then, try to put a piece of tape over the switch.
Paper-out switches are usually mechanical types of switches
that can be held down with a piece of tape.
* Electronically shorting the switch together Take the
printer apart, cut the switch out of the circuit, strip
the ends of two wires, and twist together the ends of the
wires (recommended only for techies).
The first option temporarily disables the paper-out switch
through software; then it turns the paper-out switch back
on. The second, third, and fourth options disable the paper-out
switch and are dangerous. If the printer continues printing
with no paper, the platen gets dirty and can become pitted
and harden. The print head can become damaged. Most print
heads today are made out of pot metal; the pot metal holding
the individual print head wires wears out before the wires
bend, break, or stop firing. Printing without paper will
cause the pot metal to wear out.
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