Intermec EasyCoder 301 – Service Manual Ed. 3
30
Chapter 7 Print Unit
7.5
Ribbon/Media
Sensor
Description
The ribbon/media sensor serves four purposes:
• To detect ribbon-present/out-of-ribbon conditions
1
, see chapter
6.4.
• To detect black marks printed on the backside of paper web.
• To detect slots or gaps in the paper web.
• To detect out-of-paper conditions.
The sensor module consists of a plastic moulding with two snap-
locks, that engages the centre-line wall. Inside the moulding are two
circuit boards. The sensor is connected to connector J7 on the CPU
board.
On the top side of the upper board are an IR LED (infrared light-
emitting diode) and an optical sensor that detects the presence of
any transfer ribbon, see chapter 6.4.
On the bottom side of the upper board is an optical sensor that is used
to detect gaps and slots in the paper web at a position 12 mm (0.5")
from the inner edge of the paper web. The light is emitted from an
IR LED on the lower board. To make the reading more exact, the
light must pass through a narrow slit in the plastic moulding.
On the lower board is also an optical sensor that detects light
reflected from the backside of the paper. If there is a black mark, no
light will be received.
The printer's setup decides how the signals will be interpreted. In
case of labels (w gap) or tickets (w gap), signals from the upper
optical sensor are used to detect when a gap or slot changes to paper.
In case of tickets (w mark), the lower sensor is used to detect when
a black marks starts. In case of var. length strip and fix length strip,
only out-of-paper conditions are detected.
Note that it is imperative that the sensor is free from dust, pieces of
paper or other objects that may interfere with the beam.
Replacement
• Remove the electrics cover as described in chapter 2.3.
• Disconnect the cable from connector J7 on the CPU board.
• Remove the stepper motor as described in chapter 7.3
.
• Remove the printhead as described in chapter 7.6
• Disengage the snap-locks and pull out the sensor through the
media compartment. Be careful not to damage the cable!
• Fit a replacement sensor and reassemble the printer in reverse
order. Note that the sensor's cables should run under the belts and
the stepper motor.
WARNING!
Before removing the electrics
cover, turn off the printer and
disconnect the power cord. High volt-
age wires and circuits inside.
Upper Circuit Board
Lower Circuit Board
Paper runs through this gap
1
/. Not in the LinerLess model.
