Singer HD6600C Service Manual

The Singer HD6600C is a heavy-duty sewing machine designed for advanced home sewing and light commercial use. This service manual provides detailed technical information for qualified technicians, including disassembly instructions, troubleshooting procedures, parts identification, lubrication points, and electrical schematics. Below are key sections covering safety, specifications, maintenance, repair procedures, and parts lists.

Safety Precautions

Before servicing, disconnect power. Use proper tools. Wear safety glasses.

1. Electrical Safety: Always unplug the machine from the electrical outlet before performing any service, cleaning, or maintenance.
2. Workspace: Ensure the work area is clean, well-lit, and free of obstructions.
3. Personal Protective Equipment (PPE): Wear safety glasses to protect against flying springs, clips, or lubricants.
4. Lifting: The machine head is heavy; use proper lifting techniques or assistance to avoid strain or injury.
5. Reassembly: Ensure all parts are correctly aligned and secured before applying power. Test without thread first.

WARNING! Servicing electrical components requires qualified personnel. Incorrect repair can cause shock, fire, or machine damage.

Machine Specifications

• Model: Singer HD6600C
• Type: Heavy-Duty, Computerized Sewing Machine
• Stitches: Over 100 built-in stitches, including utility, decorative, and buttonholes.
• Maximum Sewing Speed: 850 stitches per minute.
• Needle System: SINGER 130/705H (15x1)
• Presser Foot Lift: 13 mm (manual), 10 mm (optional knee lifter)
• Feed Dog: Drop feed with 7-piece feed dog.
• Hook Type: Rotary, full hook with automatic bobbin winding.
• Motor: DC Servo Motor, 110V, 60Hz (US/Canada).
• Power Consumption: 70 Watts.
• Weight: Approx. 25.5 lbs (11.6 kg).
• Dimensions (LxWxH): 17.3" x 7.9" x 12.2" (44 x 20 x 31 cm).

Tools & Test Equipment

Required for proper service and calibration.

Tool	Specification/Use
Screwdriver Set	Phillips #0, #1, #2; Flathead 3mm, 5mm
Hex Key Set	Metric: 1.5mm, 2mm, 2.5mm, 3mm
Needle Nose Pliers	For retrieving hooks, springs, and small parts
Tweezers	Non-magnetic, for precise part handling
Lint Brush & Vacuum	For cleaning lint and debris
Multimeter	Digital, for continuity and voltage checks
Timing Light (Optional)	For precise hook-to-needle timing verification
Sewing Machine Oil	SINGER Brand or equivalent high-grade lubricant
Grease	White lithium grease for specific gear points
Soft Cloths	For cleaning and wiping excess oil

External Parts Identification

Key components and their functions for reference.

1. Handwheel: Controls needle position manually; inner knob for bobbin winding disengagement.
2. Stitch Selector Dial/Panel: Selects stitch patterns and functions.
3. Stitch Length/Width Dials: Adjusts stitch dimensions.
4. Tension Dial: Regulates upper thread tension (0-9).
5. Presser Foot Lever: Raises and lowers the presser foot.
6. Bobbin Winder: Located on top, winds bobbin automatically.
7. Needle Clamp Screw: Holds needle in place.
8. Feed Dog Drop Lever: Lowers feed dogs for darning or free-motion sewing.
9. Reverse Stitch Lever/Button: Engages reverse sewing for reinforcement.
10. Power & Light Switch: Main power control and LED work light.
11. Foot Controller Jack: Connects the variable speed foot pedal.

Internal Mechanism Overview

Primary internal systems and their interaction.

• Main Shaft (Upper): Driven by motor belt; converts rotary motion to needle bar and feed dog movement.
• Hook Drive Assembly: Transfers motion from the upper shaft to the rotary hook via gears or a timing belt.
• Needle Bar Assembly: Includes needle bar, connecting link, and guide bushings.
• Feed Mechanism: Seven-piece feed dog driven by feed cam and fork lift.
• Tension Assembly: Upper tension discs, check spring, and take-up lever.
• Bobbin Case & Hook: Rotary hook assembly with bobbin case and race.
• Electronic Control Board: Manages stitch patterns, motor speed, and user interface signals.
• Motor & Drive Belt: DC servo motor connected to the main shaft via a rubber belt.

Note: Refer to exploded diagrams in Section 12 for visual reference.

Disassembly & Reassembly

Step-by-step procedure to access internal components. Perform in order.

1. Preparation: Unplug machine. Remove needle, presser foot, and bobbin case.
2. External Covers: Remove top cover screws (4x). Lift off top cover carefully, noting any wire connections.
3. Front Panel/Nameplate: Remove screws securing the front nameplate. Disconnect any ribbon cables from the control panel slowly.
4. Handwheel & Clutch: Remove handwheel set screw. Slide off handwheel and clutch assembly.
5. Motor Belt & Pulley: Loosen motor mounting screws to slacken belt. Remove belt from motor and main shaft pulleys.
6. Needle Bar & Presser Bar: Remove needle clamp screw and needle bar connecting link pin. Lower presser bar by loosening its setscrew.
7. Hook Assembly Access: Remove throat plate and bobbin cover. Remove hook race ring and shuttle/hook assembly.
8. Feed Dog Removal: Remove feed dog screws (2x) from under the throat plate. Drop feed mechanism may require lowering the feed dog first.
9. Reassembly: Reverse the order. Ensure all gears are timed correctly (see Section 8). Lubricate points per Section 10 before final closure.

CAUTION! Keep screws and small parts organized. Take photos during disassembly for reference.

Timing Adjustment

Correct hook-to-needle timing is critical for stitch formation.

1. Preliminary Check: Ensure needle is straight, inserted fully, and facing the correct direction (flat side to the back).
2. Set Needle at Highest Position: Turn handwheel towards you until the needle bar is at its highest point.
3. Hook Point Alignment: The point of the hook should meet the needle exactly at the eye (or approximately 0.04 inches/1mm above the eye) when the needle has descended about 2.5mm from its highest position.
4. Adjustment Procedure:
   • Loosen the setscrew on the hook drive gear or timing belt pulley.
   • Rotate the hook assembly slightly until the point aligns perfectly with the needle eye at the specified position.
   • Tighten the setscrew firmly while holding the hook in position.
5. Verification: Rotate handwheel slowly through a full cycle. The hook should pass the needle without touching it. Test sew with thread.

Note: Incorrect timing causes skipped stitches, thread breaks, or needle strikes.

Tension System Service

Diagnosing and repairing upper and lower thread tension issues.

Component	Symptom	Service Action
Upper Tension Discs	Uneven stitches, loose top thread	Clean lint from between discs. Check for worn or grooved discs; replace if damaged.
Tension Spring (Check Spring)	Poor thread control on underside	Adjust spring tension or replace if broken. It should provide slight resistance when thread is pulled.
Take-Up Lever	Thread breaks, erratic feeding	Inspect for burrs in the eye. Ensure smooth, full travel up and down.
Bobbin Case Tension	Loose or tight bobbin thread	Adjust small screw on bobbin case spring. Test by suspending case by thread; it should drop slightly when jerked.
Thread Path	Consistent tension problems	Ensure thread is correctly routed through all guides, discs, and the take-up lever.

Tip: Always test tension on a double layer of fabric similar to the user's typical project.

Electrical System & Motor

Testing and servicing the DC motor and control electronics.

1. Power Supply Check: Use a multimeter to verify 110-120V AC at the wall outlet and at the machine's power inlet.
2. Foot Controller Test: Disconnect foot controller. Check for variable resistance across its terminals while depressing the pedal.
3. DC Motor Test: Disconnect motor leads. Measure resistance between terminals (typically 5-20 ohms). Infinite resistance indicates an open winding; near zero indicates a short.
4. Control Board Inspection: Visually inspect for burnt components, bulging capacitors, or cracked solder joints. Check all ribbon cable connections are secure.
5. Replacement Procedures:
   • Motor: Remove belt, disconnect wires, unscrew mounting plate.
   • Control Board: Document all wire and cable connections before removal. Transfer any user-preserved settings if possible.

WARNING! Capacitors on the board can hold a charge even when unplugged. Allow time to discharge or use appropriate precautions.

Lubrication Guide

Regular lubrication ensures smooth operation and prevents wear. Use SINGER oil or equivalent.

• Frequency: After every 50 hours of use, or as part of annual service.
• Points to Oil (1-2 drops each):
  1. Needle bar bushings (upper and lower).
  2. Presser bar bushing.
  3. Take-up lever pivot point.
  4. Hook race and rotary hook bearings.
  5. Main shaft bearings (front and rear).
  6. Feed dog cam and fork lift pivot points.
  7. Handwheel shaft bearing.
• Points to Grease (Sparingly):
  • Gear teeth on hook drive assembly (if applicable).
  • Main shaft worm gear (if present).
• Procedure: Apply oil to points while moving the handwheel to work it in. Wipe away any excess oil to prevent staining fabric.

CAUTION! Do not over-lubricate. Excess oil can attract lint and gum up mechanisms.

Troubleshooting & Diagnostics

Symptom	Possible Cause	Corrective Action
Machine does not run/power on	No power, faulty switch, bad control board	Check outlet, cord, fuse. Test power switch continuity. Inspect control board.
Motor runs but needle doesn't move	Broken drive belt, disengaged clutch	Inspect and replace belt if worn/broken. Ensure handwheel clutch is engaged for sewing.
Skipped stitches	Wrong/bent needle, incorrect timing, burred hook	Replace needle with correct type. Check and adjust hook-to-needle timing. Polish or replace hook.
Thread breaks frequently	Burred needle eye/tension discs, incorrect threading, poor quality thread	Check thread path for sharp edges. Rethread correctly. Use better quality thread.
Uneven feed, fabric not moving	Feed dogs clogged with lint, feed dog height too low, presser foot pressure	Clean under throat plate. Adjust feed dog height via screw under machine. Check presser foot spring.
Unusual noise (knocking, grinding)	Lack of lubrication, foreign object, worn gears/bearings<