8
10
ASCII BIT 0
11
ASCII bit 1
12
ASCII bit 2
If you will be using the PR-40 Printer with the SWTPC 6800 Computer System,
you will need to drive it with the output half of an MP-L option on the SWTPC
6800 Computer System. Connections should be made between the two as shown in the
PR-40/SWTPC 6800 Interconnection drawing. When writing programs to drive the PR-
40 printer with the SWTPC 6800 Computer System, it will be necessary to first
configure the 6820 peripheral interface adaptor integrated circuit on the MP-L
option of the SWTPC 6800 as in the diagnostic and then use an output character
routine similar to that used in the PRNTST-1 diagnostic.
Checkout and Adjustment
For the initial testing of your PR-40 disconnect the printer solenoids by
pulling loose J2 on the PR40A board if you have the solenoids connected. In order
to checkout the printer you should use an analog type DC voltmeter having a 0-10V
scale. (Most digital meters give false readings for this particular application).
Connect the negative (-) end of your meter to the PR40's chassis or PC board
ground and hook a 4.7K ohm 1/2 watt resistor (supplied) between the + and -
terminals of your meter. Turn on the power and connect the positive meter probe
(with the 4.7K resistor attached) to the collector of Q1 on the PR-40A board (the
metal part of the case with the mounting hole in it). The voltage should read
very low and go up as you initiate your PRNTST diagnostic program. Also note that
the print motor should start up and move the head although no printing will
occur. If the voltage does not rise recheck your program. The voltage should rise
to anywhere between 1 and 6 volts depending on the setting of the density
control. Check each of the seven transistors for this voltage. If the voltage
goes beyond about 6 volts recheck your circuit board for mistakes - DO NOT HOOK
UP THE SOLENOIDS UNTIL THE PROBLEM IS CORRECTED.
After you have verified that all voltages look OK switch the printer off
and connect J2. Re-load your diagnostic and switch the printer on. Running your
diagnostic should activate the printing mechanism and printing should start. You
can now adjust the line length and print density. Adjust R25 for the print
intensity most desirable. The line width can then be adjusted by R17. Note that
if the width is extended too far the characters on the right edge will be much
narrower than normal. After the line width has been adjusted the paper can be
centered by moving the two white plastic guides on the round bar underneath the
platen at the rear of the mechanism. If necessary, the entire paper carrier can
be moved slightly by loosening the four screws holding it to the main mechanism
and sliding it to one side or the other as necessary.
The Printer Mechanics
The entire design is based on a remarkably simple and reliable print
mechanism. The printed characters are formed by moving the print head
horizontally across the paper while selectively energizing solenoid driven print
wires on the head which strike an inked ribbon and imprint dots on standard
adding machine paper. All seven of these solenoid driven print wires converge at
the tip of the print head in a vertical line which is perpendicular to the
horizontal direction of movement of the print head. By selectively firing the
print wires, 5 dot wide X 7 dot high characters are printed as the print head
moves across the paper. A one dot time spacing is left for separation between the
printed characters.