Official Elna PRO 4 DC, PRO 4 DE, PRO 5 DC, PRO 5 DE Service Manual - Comprehensive Repair Procedures

Elna Lock PRO 4DC & PRO 5DC Service Manual - 1991/1993 Edition

This professional service manual provides factory-standard calibration and repair protocols for the Elna Lock PRO series of overlock machines. Proper maintenance utilizing this data ensures the longevity of self-lubricating sintered metal bearings and avoids common timing errors during looper replacement. A critical maintenance insight involves the high-breakage capacity SPT 3.15A/250V fuse (Tavaro No. 396'900-00) required for 230V DC models; installing the incorrect low-breakage capacity variant can lead to catastrophic circuit board failure during an motor overload event.

System Classification and Technical Applicability

Computer DC Series (Micro-processor Control)

• PRO 5DC: Models featuring 5-thread capability, LCD display for thread tension, and integrated re-programming systems.
• PRO 4DC: Models featuring 4-thread capability with electronic tension reference and diagnostic display.

Electronic DE Series (Electronic Foot Control)

• PRO 5DE: 5-thread electronic models utilizing electronic motor-speed control circuits.
• PRO 4DE: 4-thread electronic models utilizing carbon-pile variable resistance bypass.

Production Variations & Serial Number Cut-offs

• Early Production: Machines up to No. 154,659 (utilizing Gauge 4633/396'001-03).
• Mid-Production: Machines from No. 154,660 to No. 182,890.
• Late Production: Machines from No. 182,891 and up (Introduction of 3-needle clamp and G-6/G-7 display circuits).

Operational Reliability & ROI proof Points

• Precision Timing Benchmarks: Detailed looper-to-needle clearances (0.05 mm) and angular positions prevent skipped stitches and needle breakage on high-speed industrial-grade seams.
• Diagnostic Efficiency: Built-in Test Program sequences for the LED/LCD display and motor circuit allow for rapid fault isolation without unnecessary parts replacement.
• Part Interchangeability: Technical modification notes track the evolution of components like the link-motion looper driving system, ensuring correct parts procurement for specific serial ranges.

Document Metadata

• Print Number: 396900-02
• Page Count: 83 Pages
• Document Type: Technical Service Manual
• Manufacturer: Tavaro s.a. Genève, Switzerland

Factory Benchmarks & Calibration Data

Mechanical synchronization requires adherence to the following factory specifications:

• Needle Bar Height: 10.5 mm to 11.0 mm depending on machine number and looper driving system version.
• Lower Looper Clearance: Positioned at less than 0.05 mm from the needle with an angular swing of 2.8 mm.
• Feed Dog Height: 1.1 mm above the needle plate using adjustment gauge 4725/396'001-04.
• Motor Speed Regulation: Max speed calibrated to 1,400 RPM (+/- 50) and Min speed (Tortoise mode) to 650 RPM (+/- 50).

Diagnostic Navigation & Electronic Schematics

• Logic Flowcharts: main diagnostic charts guide technicians through electrical failures, from power supply transformer outputs to LCD circuit board replacements.
• Wiring Topology: Detailed point-to-point wiring diagrams for 100-120V and 220-240V units, including connector pin-outs for the LP, TR2, and LCD receptacles.
• Test Program Mode: Step-by-step instructions for entering the micro-processor test mode using SW1 (+/-) and SW2 buttons to verify dot-matrix integrity and buzzer function.

Table of Contents

• General Directions: Safety, needle/thread recommendations, and lubrication points.
• Adjustments: Height and alignment of presser bar, needle bar, and loopers.
• Timing Sequences: Lower looper, upper looper, and chain looper synchronization.
• Feeding System: Vertical and horizontal feed timing, differential feed neutral position.
• Cutting Assembly: Fixed and moving cutter alignment and timing.
• Electrical/Electronics: Speed control adjustment, fuse replacement, and language selection.
• Technical Modifications: Cumulative updates from 1991 through 1993, including the Instant Rolled Hem device.

Operational Limits & Specification Standards

• Thread Tension Presets: Standard values calibrated at 55–95g depending on the specific color-coded tension unit (Blue, Red, Yellow, Green).
• Lubrication Frequency: Mandatory lubrication of the 4 red-marked oiling points every 7 to 8 hours of intensive use.
• Fuse Ratings: 100-120V units require 5A/125V Slow type; 230V units require 3.15A/250V High Breakage Capacity SPT type.
• Needle Systems: Primary use of 130/705 H (15 x 1) with recommendation for EL x 705 for optimized stitch quality.