2009 Lexmark C734n, C734dn, C734dnw, C736n, C736dn, C736dnw Service Manual (P/N 12G9820)

• Covers Lexmark C734n (5026-210), C734dn (5026-230), C734dnw (5026-280), C736n (5026-410), C736dn (5026-430), and CS736dn (5026-439), including network, duplex, and wireless configurations.
• Fault-finding sections combine POST sequencing, 1xx/2xx/3x-8x/9xx error references, print-quality symptom tables, and yes/no service checks for the printhead, fuser, EP drive, transfer module, power supplies, paper path, sensors, operator panel, networking, and option trays.
• Built-in service modes cover registration and color-plane alignment, motor and print tests, panel/button/DRAM checks, duplex setup, static and dynamic sensor tests, Mirror Motor and Servo Laser tests, device tests, event logs, motor calibration, and color-calibration resets.
• Repair coverage reaches field-replaceable unit (FRU) removal, installation, and adjustment for the printhead, fuser, Color On Demand assembly, EP drive, transfer module, photoconductors, HVPS/LVPS, system board, paper-pick and MPF/duplex mechanisms, hard drive, wireless network card, and antenna.
• Optional paper handling is documented through the 550-sheet and Specialty Media Drawers and the high-capacity input tray (HCIT), including tray-motor fault checks and removal of the controller board, elevator motor/sensor, pick rolls, photointerrupter, drawer slides, covers, and top plate.
• The 436-page PDF is Lexmark Service Manual P/N 12G9820, edition/revision dated June 8, 2009.

Technical Documentation Scope

This manual is for the 5026 family, not a generic C73x operator guide. It identifies each covered machine type and separates the C734/C736 option limits: C734 models accept up to three input options, while C736 models accept up to four, with one HCIT at the bottom of the stack. It also states that C73x media options are shared with the X73x MFP family but not with other Lexmark printers. That distinction matters when diagnosing Too Many Trays Attached or Incompatible Tray messages and when matching drawer parts.

Diagnostics, Calibration, and Major Repairs

The diagnostic material follows the 5026 control architecture instead of treating faults as generic printer errors. Error-code charts and service checks trace motor, sensor, cable, fuse, and board feedback to likely FRUs. Static and dynamic sensor tests cover input, exit, bubble, toner, narrow-media, bin-full, front-door, waste-toner, belt-waste, temperature, and toner-patch circuits; the system-board chapter then maps those functions to connector IDs and pin/signal names. Print-quality repair paths address background, blank pages, banding, residual images, insufficient fusing, missing image at the edge, and color-plane faults.

For post-repair verification, the Diagnostics and Configuration menus provide tray print tests, duplex quick and print tests, margin and skew adjustments, motor direction tests, printhead verification, event logs, page counts, fuser-count reset, and EP setup adjustments. The printhead section goes beyond removal: it covers black-plane mechanical skew and registration, followed by electrical alignment of cyan, magenta, and yellow to black.

Repair information includes cover access, cable routing, component removal, installation notes, screw and retainer identification, and ESD/photoconductor handling. The required-tools list calls out a multimeter, feeler gauges, spring hook, parallel wrap plug P/N 1319128, Twinax/serial debug cable P/N 1381963, and coax/serial debug cable P/N 1381964.

Diagrams, Specifications, and Parts Identification

Useful visual references include the Error Jam Locations map, Quick Test and color-alignment page examples, fuser autoconnect and continuity illustrations, the System Board Diagram, and exploded views for the Covers, Front, Right, Top, optional drawer, and HCIT assemblies. The parts catalog ties diagram callouts to FRU part numbers and adds a separate part-number index.

General information provides dimensions and installation clearances, memory and expansion data, supported data streams, environmental, electrical, acoustic, media, and input/output specifications. Preventive-maintenance material covers safety inspection, approved lubrication specifications, exterior and printhead-lens cleaning, and moving precautions. The fastener reference is a screw-and-retainer identification table with P/Ns, locations, and quantities rather than a torque-specification table. Electrical reference is connector-level through board maps, test points, and pin/signal tables; this is not a separate full wiring-diagram volume.

Important Service Notes

Two repair cautions are specific to this platform. For a 950.xx EPROM mismatch, only one of the system board, operator-panel card, or top-access-cover assembly may be replaced at a time; the manual warns that changing more than one can render the printer inoperable. It also flags HVPS cable orientation and camshaft-follower seating because either can create false photoconductor-missing faults after reassembly.

Service work exposes hot fuser surfaces, hazardous voltage, printhead laser exposure, ESD-sensitive boards, and a heavy base machine. Follow the manual's isolation, cooling, handling, and lifting precautions.

The PDF is unencrypted and imposes no printing restriction. Its selectable text lets you locate error codes, connector IDs, FRU names, and test titles by keyword.