HP LaserJet 4345mfp Series Service Manual, 2004 (P/N Q3942-90950)

HP's service manual for the HP LaserJet 4345mfp series, P/N Q3942-90950, Edition 1, November 2004, covers the base 4345mfp and the 4345x, 4345xs, and 4345xm configurations.

Searchable Service Text and Circuit Detail

Text search and circuit labels: The manual body has searchable PDF text and embedded bookmarks for chapters and subsections. Small pin numbers and signal labels in the dense circuit diagrams are readable when enlarged.

The ZIP download contains one printable English PDF with 650 pages. This total includes 618 pages in the main numbered sequence and 32 pages of covers, front matter, and closing material.

Print-Engine, Scanner, and Paper-Path Service

These selected service topics summarize key areas rather than reproduce the full table of contents. Further topics include Secure Disk Erase settings and real-time clock configuration.

• Print-engine and electrical theory: Formatter and DC controller PCA operation, engine power supply, fuser-control and high-voltage circuits, laser/scanner control, image formation, motors, fans, and operating sequences.

• Component removal and replacement: Illustrated step-by-step procedures for the fuser, transfer roller, registration and reversing assemblies, DC controller, scanner/ADF components, and 500-sheet feeder.

• Paper-path and finishing systems: Pickup, feed, skew correction, fusing, reversing, and delivery through the core engine, optional feeders, duplexer, 3-bin mailbox, stapler/stacker, and ADF.

• Factory diagnostic procedures: Power-on fault isolation, control-panel messages, jam and image-defect charts, repetitive-defect ruler, paper-path and manual-sensor tests, scanner tests, and functional checks.

• Maintenance and service controls: Scanner calibration, print-engine and ADF maintenance, counter resets, firmware upgrades, event logs, NVRAM and hard-disk initialization, and formatter-replacement settings.

• Circuit and location references: Electrical circuit diagrams, controller connections, sensor and switch locations, operating-timing charts, and illustrated parts references for fault tracing and replacement planning.

Its internal repair procedures and powered diagnostic checks make it best suited to professional printer technicians and repair shops familiar with LaserJet operation and equipped for ESD-safe electronic service.

Configurations and Assembly-Level Repair

The 4345x adds a duplexer, an additional paper feeder, and analog fax to the base model. The 4345xs adds the x-model hardware plus a stapler/stacker and cabinet; the 4345xm combines the x-model hardware with a 3-bin mailbox and cabinet.

Internal service procedures extend to the feed-roller assembly, main motor, paper-pickup and lifter drives, power-factor-correction and engine power supplies, paper-feed assembly, and laser/scanner. Scanner coverage includes the glass, optical unit, lamp, inverter PCA, fan, home-position sensor, and scanner-controller PCA. Formatter hardware procedures address the hard drive, DIMMs, firmware flash card, and analog fax accessory.

Repairs are primarily at the field-replaceable assembly or subassembly level. HP does not support replacement of individual components on printed-circuit assemblies.

The core MFP, scanner/ADF, and 500-sheet feeder receive detailed removal and replacement coverage. Duplexer and output-accessory coverage includes operating theory, jam diagnosis, accessory-light interpretation, replacement-level parts views, and assembly part numbers. There is no full internal overhaul chapter for the stapler/stacker or 3-bin mailbox.

Basic fax setup checks and fax-accessory replacement are included. Full fax troubleshooting requires the separate HP LaserJet Analog Fax Accessory 300 Service Manual, which is not included in this download.

Fault Isolation, Calibration, and Service Settings

Troubleshooting distinguishes print-engine faults from scanner/ADF, formatter, and connectivity problems. Engine, formatter, half self-test, and drum-rotation checks support image-formation diagnosis. Individual component tests exercise motors, solenoids, and clutches, helping isolate a fault before parts are removed.

Configuration, supplies-status, usage, event-log, and Jetdirect pages support diagnosis and maintenance planning. Digital-sending checks address SMTP and LDAP gateways; network diagnosis includes loopback and ping tests.

Scanner calibration uses a printed target to calculate and store carriage-head offset corrections for ADF and flatbed scans. An ADF transferred to another scanner requires recalibration.

Preventive-maintenance coverage distinguishes the print-engine kit's fuser and rollers from the document-feeder kit's pickup assembly, separation pad, and mylar components, with related counter-reset procedures. Service-menu references cover page counts, serial-number entry, default paper size, and Service ID restoration after formatter replacement.

Parts Identification and Electrical References

The illustrated parts catalog provides exploded views, reference numbers, quantities, and HP part numbers for external panels, the electrical/forward section, drives, registration and delivery assemblies, fuser, ADF, scanner, feeder, and replaceable accessories. Alphabetical and numerical indexes support parts lookup.

Engine references include the DC controller PCA block diagram and Laser-control-circuit block diagram. The ADF paper path and sensors, DC controller component connections, General timing chart, and Circuit diagram for the scanner support transport and electrical fault tracing.

Reference tables cover physical, environmental, electrical, acoustic, image-area, and supported-media specifications. A compatibility table distinguishes selected LaserJet 4200- and 4300-series parts that can and cannot be used in this MFP.

Scanner Service and Handling Cautions

Optical-unit service notes explain how incorrect cable routing can restrict carriage travel. Lamp-handling cautions identify skin oils as a cause of image-quality defects and possible lamp damage.

HP directs technicians to disconnect power before removing assemblies, use ESD protection around sensitive electronics, allow the fuser to cool, and never operate or service the machine with the laser/scanner protective cover removed.

Examples of Roller Defect Spacing and Page Skew

The repetitive-defect table associates a 47.0 mm repeat distance with the transfer roller. Its roller-by-roller references connect repeating image marks with the relevant replacement assemblies.

For cut-sheet paper, the print-engine skew specification is less than 1.5 mm over a 260 mm length. Separate limits are provided for envelopes and for ADF and flatbed scans.