1991–1993 Elna Lock PRO 4 DC/DE & PRO 5 DC/DE Overlock Sewing Machine Service Manual (P/N 396900-02)

Tavaro S.A. Genève's Elna Lock Service Manual P/N 396900-02 covers the 1991–1993 PRO 4 DC, PRO 4 DE, PRO 5 DC, and PRO 5 DE overlock sewing machines. DC models use computer control; DE models use electronic foot control.

• Needle and looper timing: Cloth presser bar alignment, needle bar height and eccentric alignment, upper/lower looper synchronization, and PRO 5 chain looper adjustments.

• Feed and cutting systems: Feed dog height, vertical and chain-stitch feed timing, differential feed neutral position, and fixed/moving cutter setup.

• Thread tension and take-up: Needle and looper tension calibration, tension release, take-up lever placement, thread guides, and chain needle check-spring conversion.

• Mechanical drive: Motor belt tightness, balance weight positioning, and eccentric alignment following lower-shaft disassembly.

• Electrical diagnosis: DC test program, diagnostic flowcharts, circuit measuring points, display mode selection, and DE foot controller starting-speed and fuse procedures.

• Technical modifications: Earlier and revised needle clamps, looper drive assemblies, LCD/LED display boards, and rolled/narrow-hem device installation.

This manual is suited to sewing-machine repair technicians familiar with timing adjustments and electrical testing using a voltmeter and ohmmeter.

Mechanical Adjustments and Sewing Faults

The Mechanical Sewing Disorders charts connect skipped overlock or chain stitches, thread breakage, irregular stitches, and broken needles with the relevant adjustments. These references help narrow a repair to the affected timing, tension, feed, or thread-path checks.

On PRO 5 machines, horizontal feed timing affects chain-needle entry into its guard; incorrect timing can bend the needle in thick material. The moving cutter and chain looper share an eccentric, so their timing adjustments are linked.

The gauge section identifies 4633/396'001-03 and its replacement, 4725/396'001-04, including the additional mark for earlier take-up levers.

DC Diagnostics and DE Foot Controls

The integrated DC test program checks the LCD and LEDs, display-mode switches, program-key buzzer, foot control response, and overload safety cut-off. The electrical diagnostic charts distinguish a dead display, a failed sewing lamp, a motor that will not run, and an unresponsive speed control.

Check/Measuring Points in Electric Circuit and Power Control Circuit provide connector locations, wire colors, and voltage/resistance tests for the transformer, LCD supply, motor, and lamp circuit. The manual distinguishes AC transformer outputs from the DC supply to the LCD.

Speed-calibration instructions cover checks after control-board or motor replacement. DE coverage includes the 4C-335B/G electronic foot controllers and Wiring Diagram 4DE, 5DE for both mains-voltage versions. Their fuse specifications differ from the DC main-board fuse ratings.

Crossing the lamp, LCD, and foot-control connectors can damage the LCD display or main control unit. Before attempting any internal diagnostics, review the included safety recommendations regarding power disconnection and proper needle selection to prevent injury or equipment damage.

Serial Changes and Retrofit Compatibility

Serial references belong to individual component changes. The Height and Orientation of Needle Bar summary and looper-drive modification sheets distinguish earlier mechanisms from the later link-motion system, with different needle-bar settings for affected PRO 5 DC builds.

Display updates distinguish G-5, G-6, and G-7 LCD/LED boards. Fitting a later sewing guide to an earlier two-needle PRO 5 DC also involves needle-clamp and needle-bar compatibility.

Rolled/narrow-hem retrofit instructions identify separate PRO 4 and PRO 5 devices, which are not interchangeable. G-5/G-6 displays lack the later hem-device indication, while G-7 provides it. The PRO 5 retrofit also requires the revised chain-stitch sewing table.

The modification sheets include replacement-part references and an exploded looper-drive view for repair work. The full parts catalog is a separate publication.

PDF Navigation and Diagram Readability

Text search and embedded PDF bookmarks are not available; the printed index provides section references. Small connector and pin labels on the DC circuit pages are readable when enlarged. This printable, English-language 83-page PDF includes 25 numbered technical-modification pages, one additional exploded-parts sheet, the cover and index, and six blank pages, all within the total.