4. There are two potentiometers located on the Logic (OEM) board (R2 + Rll). Potentiometer Rll (optic
sensor adjustment) often has to be adjusted when the Logic (OEM) board is replaced.
a. R2 (labeled R4 on some boards) adjusts the length of the print pulse. If this adjustment is off, the
result could be
light
or
no print
or activation of the two-second jam circuit which causes the drive
motor to shut off. This adjustment should be made with an oscilliscope by following the procedure
in Section 5.4.8 of the “Printer Service Instructions” (Pub. No. 575-527). If a scope is not available,
this adjustment can be made by following this procedure.
1. Sequentially set switches 3,7, and 8 of switch-package Q on to drive the head printing the char-
acter H.
2. If the head stops during adjustment, reset the two-second jam circuit by turning switch 8 off
and then on.
3. Adjust potentiometer R2 so that the print is neither too light nor too heavy. (Counterclockwise
lengthens print pulse and clockwise shortens print pulse.) Do not run continuously for more
than five minutes without pausing for an equal length of time.
4. Sequentially turn off switches 8,7, and 3.
b. Potentiometer Rll adjusts the optical sensor on the printhead. If this adjustment is off, you could
be
missing vertical dot columns
or have
no print.
It could also cause activation of the two-second
jam circuit which causes the drive motor to shut off. This adjustment should also be made with a
scope in accordance with the procedure in Section 5.4.9 of the “Printer Service Instructions” (Pub.
No. 575-527). If a scope is not available, this adjustment can be made by following this procedure:
1. Sequentially set switches 3,7 and 8 of switch-package %I on to drive the head printing the char-
acter H.
2. Adjust potentiometer Rll so that there are no missing dots in the pattern. Do not run continu-
ously for more than five minutes without pausing for an equal length of time. Otherwise, the
result could be solenoid overheating and failure.
3. If the printhead stops during adjustment, reset the two-second jam circuit by turning switch %
off and then on.
4. Rotate Rll clockwise until misprinting occurs (note position of Rll) and then counterclock-
wise until misprinting occurs (again note the position of Rll). Set the potentiometer in the middle
of the two positions noted above.
5. Sequentially turn off switches 8,7 and 3.
5. With the printer in self-test, there should be 120VAC to the print motor between motor leads J3-8 (yellow)
and J3-10 (black). If pots R2 and Rll are not adjusted properly, the two-second jam circuit could cut
power to the drive motor.
6. The 30 (*0.3) VDC used by the printhead can be checked between J2-8 (+30VDC) and J2-10 (common)
on the Logic (OEM) board. Refer to Section 5.3.2.2 of the “Printer Service Instructions” (Pub. No. 575-
527).
7. Missing vertical dot columns can be caused by a dirty timing rack. If dirt particles are in the rack, re-
move with a soft brush or forced air.
Ed 8 82
12
575-531
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