E320: Unexpected activation of zero position sensor on primary collimator/
E321: Timeout of zero position sensor on primary collimator /
E322: Zero position sensor for CEPH never primary collimator /
E323: Zero position sensor for CEPH always active collimator

All the messages refer to the optical barrier that is sensing the zero
position of the primary beam collimator, that is moved by a stepper
motor. This mechanism is located in front of the tube head assembly. The
slit collimator does not move during the PAN examination, while it has a
scanning motion during Ceph exams, synchronously with the secondary
collimator and CEPH sensor holder.

Also in this case, the first one (E320) may occur at the end of an
examination, while the system is checking the correctness of the motion,
meaning that the senor activation has occurred before the expected time.
This can be caused by the loss of motion of the stepper motor.

The last 3 messages are displayed during the power on phase, when the
system is controlling the functionality of the whole system.
E321 and E322 mean that the zero sensor position is never activated;
due to a motor not running or to a fault of the optical barrier (the sensor
or its harness); E323 means that this sensor position is always activated.
Also in this case the fault can be the motor or the optical barrier.

• Power off the system and remove the frontal cover of the tubehead
assembly.

• Check that during the power on phase there are movements on the
primary slit collimator; the normal motion is going to engage the
sensor and a reverse motion to disengage it. If no motion is observed,
the fault can be the stepper motor M5 or the cable connecting it to
the main CPU. Check that the cables between the motor M5 and X64
is well inserted, as for the cable X64 to X29 and X30 of the main CPU
A5.

• Check continuity of the above cables, from M5 to X64 and from X64
up to X29 and X30 of the main CPU A5.

• Repeat the power on sequence, verifying the motion.
If still there is no motion, replace the stepper motor and, if not fixed,
replace the CPU.
If a motion has been observed, but messages are displayed, this can be
the sensor or its wiring.

• Power off the system and try to manually disengage the sensor, taking
care of a smooth motion.

• Power on the system and check the functioning of the sensor,
measuring the DC voltage on the terminal of the sensor B8, with and
without an obstacle manually inserted. A variation of about 3.5 V
minimum should be observed. If not, replace the sensor.

• If the variation is observed and the message still continue to be
displayed, check the correct insertion of the cable from the sensor B8
to X58 and from that connector to X31 of the main CPU A5; check
continuity of the interested wires and replace the faulty one (if any).

• If all cables are OK, the fault is on the CPU, so replace it.