HP Color LaserJet 3500/3700 Service Manual – 2003 (P/N Q1321-90930)

This service manual provides technical documentation for the HP Color LaserJet 3500 and 3700 series printers, including the 3500n, 3700n, 3700dn, and 3700dtn configurations. Edition 1, November 2003 (P/N Q1321-90930), covers printer operation, diagnosis, maintenance, and repair through assembly replacement.

Searchable Text, Bookmarks, and Circuit Diagram Detail

Text search and diagram navigation: Searchable text and tables, internal cross-references, and embedded PDF bookmarks support navigation. Small labels in the dense general circuit diagrams are readable when enlarged; rotating the page also helps. Some diagram and flowchart labels are not searchable.

Supplied as one printable English PDF with 550 pages total: 12 preliminary pages plus 538 numbered pages through the index. Covers, contents, and blank divider pages are already included in that total.

Engine Control, Fault Testing, and Assembly Service

The following topics are a selection of the manual’s contents. Other covered subjects include PowerSave settings and control-panel security.

• Engine and image formation: Covers DC controller operation, laser/scanner control, video-interface timing, image drive mechanisms, transfer processes, and duplex paper handling.

• Electrical assemblies: Details the formatter PCB, high- and low-voltage power supply PCBs, memory controller PCB, and control panel PCB, with connector locations and replacement procedures.

• Service components: Includes removal and replacement of the transfer unit, fuser assembly, Tray 1 pickup roller, registration clutch, drum motor, exhaust fan, and media sensor.

• Fault diagnosis: Combines error messages, status codes, paper-path sensor tests, component tests, Print/Stop testing, and repetitive-defect identification for print-quality and feed problems.

• Configuration and maintenance: Covers Jetdirect networking, optional Tray 3, cleaning, calibration, NVRAM initialization, and configuration requirements after replacement of major assemblies.

Troubleshooting assumes a basic understanding of color laser printing; the removal and replacement chapter is intended for authorized service personnel.

Engine Control, Fusing, and Image Formation

The Basic operation sequence table and Power-on sequence diagram explain transitions from startup to printing. The DC controller circuit diagram connects engine control with scanner motor control and the video interface; timing charts and solenoid/clutch function tables support paper-path diagnosis.

Fuser temperature control: The Heater temperature control circuit identifies main thermistor TH1 and sub-thermistor TH2, including TH2’s startup-monitoring role. The DC controller CPU issues the Fuser Heater Drive signal (FSRD) through the ASIC.

The high-voltage section explains secondary-transfer current feedback through TR2S. Image formation system diagrams relate charging, exposure, development, transfer, and cleaning to the printed image.

Error Diagnosis, Paper Paths, and Print Quality

Alphabetical and numerical message tables link symptoms to diagnostic checks and replacement decisions. Troubleshooting flowcharts, sensor-state tables, connector location views, and general circuit diagrams support checks of pickup, registration, delivery, and the duplexing feed unit.

The repetitive-defect ruler connects recurring mark spacing to particular rollers, the drum, or fuser components, helping narrow the likely source before parts are selected. Engine and formatter test pages help distinguish print-engine faults from formatter problems.

Paper Path Test options distinguish input-tray and duplex-path problems. The Manual Sensor Test tables identify model-dependent sensor displays; the secondary transfer roller engaging sensor, PS16, is handled separately from these sensor tests.

Assembly Replacement and Configuration

Step-by-step removal and replacement procedures cover the laser/scanner assembly, image drive assembly, and internal circuit boards, with exploded parts illustrations for identification. The service approach centers on field-replaceable units; HP does not support component-level repair of printed circuit boards.

Fuser and laser/scanner limits: Internal fuser parts such as thermistors and the fuser sleeve are serviced by replacing the complete fuser assembly. The laser/scanner unit is not intended for disassembly or adjustment.

Incorrect positioning of the print-cartridge engaging pins during reassembly can damage the pins, print cartridges, or swing guide closing mechanism.

Replacing the formatter and DC controller together can erase duplex capability on duplex-equipped 3700 models. The manual specifies a printer-specific PJL file from HP for recovery.

Replacement configuration procedures address NVRAM initialization, calibration, fuser and transfer-unit counters, and restoration of printer identity and configuration data. Parts lists distinguish model-specific and voltage-specific assemblies.

Optional hardware: Configuration and site-requirement sections cover Jetdirect networking and optional Tray 3. Procedures for 168-pin DIMM upgrades apply to the 3700 series; automatic duplexing coverage applies to the 3700dn and 3700dtn.

Tray 3 service extends beyond installation to replacement of its pickup roller, separation pad, pickup clutch, solenoid, sensor, and PCB.

Safety note: High-voltage components and a hot fuser are present. Follow the manual’s electrical, laser, and electrostatic-discharge precautions before opening the printer chassis or servicing internal assemblies.

Selected Handling and Fuser Diagnostic Data

With print cartridges installed and without optional Tray 3, printer weight is 36.6 kg for the 3500 series and 37.8 kg for the 3700 series.

For the removed fuser at ambient temperature, the main-thermistor check specifies 50–330 kΩ, while the heater circuit specifies 12–52 Ω. These values appear in the INSTALL FUSER troubleshooting entry alongside connector identification and replacement criteria.