Singer 900 Series Service Manual

The Singer 900 Series represents a line of premium sewing machines designed for advanced home sewing and light commercial use. This service manual provides comprehensive technical information for authorized service technicians, covering the 901, 902, and 903 models. It includes detailed instructions for disassembly, troubleshooting, adjustment, lubrication, and reassembly to ensure proper maintenance and repair. Below are key sections covering safety, specifications, maintenance procedures, and troubleshooting guides.

Features at a Glance

Key components: High-torque DC motor, computerized stitch selection panel, automatic needle threader, drop-in bobbin system, built-in LED lighting, heavy-duty metal frame, and multiple presser feet.

Feature	Description
Motor Type	High-torque, brushless DC motor with speed control
Stitch Selection	Computerized panel with 900+ stitch patterns
Needle System	Automatic needle threader and positioning
Bobbin System	Top-loading, jam-proof drop-in bobbin
Lighting	LED work area illumination
Frame Construction	Heavy-duty full metal internal frame
Presser Feet	Includes buttonhole, zipper, quilting, and walking foot
Feed System	Advanced drop feed with adjustable pressure
Display	LCD screen showing stitch selection and settings
Power Requirements	110-120V AC, 60Hz (US/Canada models)

Safety Precautions

Always disconnect the power cord before performing any service or maintenance.

1. Electrical Safety: Unplug the machine from the power outlet before opening any covers or removing panels.
2. Personal Safety: Wear safety glasses when working with springs, gears, or under tension. Keep fingers clear of moving parts.
3. Work Area: Ensure a clean, well-lit, and stable work surface. Keep tools organized.
4. Component Handling: Handle electronic boards by the edges. Avoid static discharge by using an anti-static wrist strap.

WARNING! The machine contains capacitors that may hold a charge even when unplugged. Allow sufficient time for discharge before servicing internal electrical components.

Technical Specifications

• Models Covered: Singer 901, 902, 903.
• Stitches: 900+ including utility, decorative, stretch, and buttonhole stitches.
• Maximum Sewing Speed: 850 stitches per minute.
• Stitch Length: Adjustable from 0-5 mm.
• Stitch Width: Adjustable from 0-7 mm (for zigzag and decorative stitches).
• Needle Positions: Left, center, and right needle stop positions.
• Presser Foot Lift: Manual and optional knee lifter; height adjustable.
• Hook Type: Rotary, full oscillating hook.
• Bobbin Size: Class 15 (transparent).
• Weight: Approx. 22 lbs (10 kg).
• Power Supply: 110-120V AC, 60Hz, 0.7 Amps.

Tools & Equipment Required

Standard and specialized tools needed for servicing the Singer 900 Series.

1. Screwdrivers: Phillips #0, #1, #2; Flathead 3mm, 5mm.
2. Hex Keys (Allen Wrenches): Metric set (1.5mm to 5mm).
3. Pliers: Needle-nose, long-nose, and diagonal cutters.
4. Lubricants: Singer Machine Oil (or equivalent light sewing machine oil), white lithium grease for gears.
5. Cleaning Supplies: Soft brushes, lint-free cloths, compressed air.
6. Measuring Tools: Feeler gauges (0.1mm to 1.0mm), seam gauge, small ruler.
7. Specialized Tools: Hook timing gauge (Singer P/N 62098), bobbin case tension spring tool.
8. Multimeter: For electrical diagnostics.

External Parts Identification

Front Panel: Stitch selection buttons, LCD display, speed control slider, reverse stitch button, needle up/down button. Top Assembly: Handwheel, spool pins, thread guides, tension dial, presser foot lever. Free Arm: Needle plate, feed dogs, bobbin cover, accessory compartment.

Rear/Side: Power switch, power cord socket, foot pedal connector, handwheel release, carrying handle.

Internal Mechanism Overview

Main components: Main shaft, hook drive assembly, feed dog mechanism, tension assembly, motor and belt drive, main circuit board, stitch cam assembly, bobbin winder mechanism.

1. Main Shaft: Driven by motor via timing belt; connects to needle bar and feed mechanism.
2. Hook Drive: Transfers motion from main shaft to rotary hook.
3. Feed Mechanism: Four-motion feed dogs driven by feed cam.
4. Tension Assembly: Includes tension discs, check spring, and take-up lever.
5. Motor: DC brushless motor with integrated control circuit.
6. Circuit Board: Controls stitch patterns, motor speed, and user interface.

Disassembly Procedure

Follow steps in order. Document and organize removed screws and parts.

1. Unplug machine and remove accessory tray, spool pins, and removable covers.
2. Remove top cover screws (4x) and lift off top housing.
3. Remove front faceplate screws (2x) to access stitch selection panel connections.
4. Disconnect motor wiring harness connector from main board.
5. Remove handwheel set screw and handwheel.
6. Remove needle plate screws (2x) and needle plate.
7. Remove bobbin case and shuttle race.
8. Remove lower cover screws (4x) to access internal mechanisms.
9. Support main shaft before removing timing belt.

CAUTION! Note the orientation of gears and cams before removal. Take photos if necessary.

Adjustment & Calibration

Critical adjustments for optimal performance.

1. Hook Timing: With needle at highest position, hook point should be 0.04-0.08 inches (1-2 mm) above needle eye. Adjust by loosening hook drive set screw.
2. Needle Bar Height: Top of needle clamp should be flush with bottom of needle bar bushing at lowest position.
3. Feed Dog Height: At highest point, feed dogs should protrude 0.04 inches (1 mm) above needle plate. Adjust via feed dog height screw.
4. Bobbin Case Tension: Thread should pull smoothly with slight resistance. Adjust small screw on bobbin case.
5. Upper Thread Tension: Calibrate so balanced stitch forms on test fabric. Adjust tension dial spring tension if necessary.

Lubrication Points & Schedule

Use Singer Machine Oil or equivalent light mineral oil. Apply sparingly.

Component	Lubricant	Frequency	Notes
Main Shaft Bearings	Light Oil	Every 500 hrs	2 drops each
Hook Race	Light Oil	Every 50 hrs	1 drop
Needle Bar Bushings	Light Oil	Every 100 hrs	1 drop each side
Feed Dog Mechanism	Light Grease	Every 1000 hrs	Thin coat on cams
Handwheel Bushing	Light Oil	Every 200 hrs	1 drop
Motor Bearings	N/A	Sealed for life	Do not oil

Tip: Wipe away excess oil to prevent attracting lint and dust.

Electrical System & Motor

The 900 Series uses a computerized control system. The main PCB receives input from the front panel and foot pedal to control the DC motor and stitch selection mechanisms.

1. Power Supply: Converts 120V AC to low-voltage DC for the control board and motor.
2. Main PCB: Central processor for all functions. Check for blown fuses (F1: 2A) or burnt components.
3. Motor: Brushless DC motor. Test resistance between terminals (should be 5-10 ohms).
4. Foot Pedal: Variable resistor. Check for smooth resistance change (0-10k ohms).
5. Connectors: Inspect all ribbon cables and harness connectors for secure seating and corrosion.

WARNING! Only qualified personnel should attempt repairs on the main PCB. Consider board replacement for complex faults.

Troubleshooting & Diagnostics

Symptom	Possible Cause	Corrective Action
Machine does not power on	Power cord, switch, fuse, main PCB	Check wall outlet, cord continuity, power switch, fuse F1 on PCB.
Motor runs but needle doesn't move	Timing belt broken/disengaged	Inspect and replace timing belt. Ensure handwheel clutch is engaged.
Uneven or skipped stitches	Needle, timing, threading, tension	Replace needle, check hook timing, rethread top and bobbin, adjust tensions.
Thread bunching under fabric (bird nesting)	Bobbin threading, upper tension	Rethread bobbin ensuring correct direction. Increase upper tension.
Feed dogs not moving	Feed mechanism disengaged, broken part	Check feed dog position lever. Inspect feed cam and forks for damage.
Error code on display (e.g., E1, E5)	Sensor fault, motor fault, PCB issue	Refer to specific error code in manual. Check position sensors and motor connections.
Loud noise or grinding	Lack of lubrication, foreign object, worn gear	Clean and lubricate hook area. Inspect for lint/jammed thread. Check gears for wear.
Stitch pattern incorrect	Stitch cam, pattern selector, PCB	Check stitch cam engagement. Test pattern selector buttons. Consider PCB issue.

Reset Procedure: Unplug machine for 2 minutes to reset the computerized system.

Reassembly Instructions

Reverse the disassembly procedure, paying attention to alignment and torque specifications.

1. Reinstall internal mechanisms (feed, hook, main shaft). Ensure timing marks align.
2. Reinstall and tension the timing belt. Check handwheel turns freely.
3. Reconnect all electrical harnesses to the main PCB securely.
4. Reinstall bobbin race and needle plate. Torque screws to 5 in-lb.
5. Replace front faceplate and top housing. Torque cover screws to 3 in-lb.
6. Reinstall handwheel, accessory tray, and spool pins.
7. Perform functional test: Run machine without thread, then with thread on test fabric.
8. Verify all adjustments (timing, tension) are correct after reassembly.

Parts List & Diagrams

Key replacement parts for Singer 900 Series (consult official Singer parts catalog for complete list and current part numbers).

• Needle Bar Assembly: Singer P/N 500200
• Rotary Hook Assembly: Singer P/N 500450
• Timing Belt: Singer P/N 620150
• Main Circuit Board (PCB): Singer P/N 700301 (901), 700302 (902), 700303 (903)
• DC Motor Assembly: Singer P/N 800100
• Foot Control Pedal: Singer P/N 400100
• Power Supply Cord: Singer P/N 300050
• Feed Dog Set: Singer P/N 550100
• Bobbin Case: Singer P/N 250100