Avery Berkel CX20 SERIES, Service Manual

Page: 205 / 353

20 — Label and Receipt Printer
20–5 CX20/CX30/CX34 Service Manual
The stepper motor is a two–coil unit and is mounted on the printer spine by two
stand–off pillars. The motor is supplied with power by two integral pairs of wires
which connect directly to the wiring harness of the printer. The drive from the
motor is transmitted through a rotary output shaft, on which is mounted a
splined, drive gear. The splined drive gear is secured in position by a
socket–headed, recessed, grub screw.
The print head is trapped between the printer spine and a bracket attached to
the spine by three stand–off pillars. A spring–loaded catch (operated by lever
outside bracket) also is carried between the spine and the bracket and, when
applied (by pushing lever fully down), brings the print head into contact with the
rubber drive roller, where the paper is carried. When in contact with the drive
roller, there is sufficient paper contact to allow printing and, also, the entrapment
of the paper between the roller and the print head enables sufficient friction grip
for the roller to draw the paper off the paper roll.
The print head prints by thermal means and has a life expectancy of 50
kilometres (30 miles) of paper. It is driven by power supplies and data received
from an external source through a ribbon cable. Its assembly makes use of
holes positioned in its carrying equipment (the bracket and printer spine), and it
cannot function nor be installed otherwise. Other than removal for maintenance
or exchange, the print head must not be further disassembled. The print head
itself is made of precision–manufactured materials and must not be scratched or
scored: avoid any contact with metal objects (such as a screwdriver blade).
A photodetector is attached to a bracket on the printer spine by a screw and a
shakeproof and plain washer. The bracket is attached to the printer spine by a
nut and shakeproof washer on its stud and also utilises the photodetector
attachment. The photodetector consists of an optical transmitter and receiver:
the transmitter transmits light directly to the receiver. Paper, from the paper roll,
is passed through a gap between the transmitter and receiver. Under the
control of software on the main PCB, the photodetector is able to detect when
there is translucent paper (backing roll) and ticket in the gap, and when
translucent paper only is in the gap. By this method, the software is able to
interpret the position and length of each label as it passes through the
photodetector, to ensure correct print positioning.
The photodetector is connected by two pairs of wires to a flying lead. Its
position is adjustable: its unsecured end is cradled in a bracket secured to the
spine, and the bracket can be rotated to reposition the photodetector through a
limited range of movement.
20.2 Test and Adjustment
The printer is scanned at power–up and will print a test ticket (or labels)
provided the keyswitch is switched to supervisor mode. The printer cannot be
tested when not installed in a unit.
To adjust the current drawn by the stepper motor, which is controlled by a
potentiometer on the main PCB (refer to Section 11), proceed as follows:
1 Using a DVM, measure operating voltage across connections of
two–pin connector SK1 on main PCB when printer is operating.
Voltage should be 3.7V (Rohm label and receipt printer). If necessary,
adjust voltage by adjusting RV3 on main PCB.