Chapter 13 - Troubleshooting Guide; Operation Sequence; Power-Up Self-Test; Print Command - Printronix L1024 Maintenance Manual

Chapter 13
Troubleshooting Guide

Operation Sequence

Knowing the sequence of operation of the printer is useful as a guide in determining what component is at
fault for a given failure. Follow the sequence below to the point where the printer fails. This will be a good
starting point for further troubleshooting of the printer.

Power-Up Self-Test

When the printer's AC power is turned on, the first things that occur are the Engine Controller Board and
Data Controller Board self-tests. Each controller board runs its own self-test independently from the other.
At the completion of a successful self-test, the Engine Controller sends a PPRDY command to the Data
Controller, and the Data Controller returns a CPRDY command to the Engine Controller. These signals tell
each board that the other board has passed its self-test and is prepared to communicate. The Engine
Controller Board then initiates the engine self-test sequence, as follows:
The Engine Controller first verifies that the top cover is closed, then checks the paper jam sensor in the
fuser. Next, the Engine Controller checks the paper empty sensor to see if there is paper present in the
printer. The erase LEDs and the stepper motor are then turned on, followed by the fuser heater. The
developer, OPC drum, and fuser cam motors are all cycled to check for proper operation. While the
developer is being cycled, the toner sensor is checked to verify that it is functioning. Once all of these
have been verified, the Engine Controller tests the LSU to ensure that it is functioning correctly. The
polygon motor, the beam detector, the laser, and the laser power circuitry are all tested in this step.
The fuser must reach operating temperature within 2 minutes after it is turned on. After the fuser has
reached fusing temperature, the Engine Controller checks for top of form (TOF) registration. If the TOF
sensor is tripped by the plastic TOF lever (flag assembly), the Engine Controller will not try to seek TOF. If
the sensor is not tripped, the Engine Controller will set TOF by moving paper into the proper position.
To set TOF, the stepper motor, electric clutch, and fuser cam motor are all activated. The fuser closes,
then the tractor feeds paper into the printer until the paper depresses the TOF lever. The fuser then
begins to pull the paper through the printer slightly faster than does the tractor. The Engine Controller
monitors the pulses from the tractor encoder wheel to ensure that the paper is moving at the proper
speed. If the encoder malfunctions during TOF registration, the paper will move about 1/2 inch before a
"Paper Jam" error occurs.
The Engine Controller feeds two sheets of paper into the printer so that the perforation for the next sheet
to be printed is aligned with the OPC drum.

Print Command

Once the Data Controller Board has sent a print command to the Engine Controller Board, the printer
performs the following steps. If the fuser is below the fusing temperature, the Engine Controller turns on
the fuser lamp to heat the fuser. Once the fuser is at the fusing temperature, the Engine Controller turns
on the erase LEDs and the stepper motor. Next, the Engine Controller activates the LSU and checks it for
proper functioning. This completes the initialization process for the printer.
After initialization has been completed, the Engine Controller Board activates the High Voltage Power
Supply (HVPS), supplying high voltages where needed throughout the printer. The Engine Controller then
closes the fuser and pulls the VSREQ signal to the Data Controller Board low, which asserts "Vertical
Synchronization Request" to the Data Controller. In response, the Data Controller pulls the VSYNC signal
Chapter 13 – Troubleshooting Guide 13–1