Kenwood CS 4125 Service Manual

The Kenwood CS 4125 is a 40MHz dual trace oscilloscope designed for professional and educational use. This service manual provides comprehensive technical information including specifications, circuit diagrams, calibration procedures, troubleshooting guides, and maintenance instructions for qualified service personnel. Below are key sections covering technical details, operation, maintenance, and repair procedures.

1. Technical Specifications 2. Front Panel Controls 3. Rear Panel Connections 4. Operating Instructions 5. Block Diagram 6. Circuit Description 7. Calibration Procedures 8. Troubleshooting Guide 9. Parts List 10. Schematic Diagrams 11. Safety Precautions

Technical Specifications

Key technical parameters and performance characteristics of the Kenwood CS 4125 oscilloscope.

ParameterSpecification
BandwidthDC to 40MHz (-3dB)
Sensitivity1mV/div to 5V/div (1-2-5 sequence)
Time Base0.2μs/div to 0.2s/div
Input Impedance1MΩ ±2% || approx. 25pF
Max Input Voltage400V (DC+AC peak)
Display8cm x 10cm CRT with internal graticule
Power Requirements100/120/220/240V AC, 50/60Hz
Dimensions300(W) x 150(H) x 420(D) mm
WeightApprox. 7.5 kg
Operating Temp0°C to 40°C

Front Panel Controls

Description and function of all front panel controls and indicators.

  1. POWER: Main power switch with indicator lamp
  2. INTENSITY: Controls trace brightness
  3. FOCUS: Adjusts trace sharpness
  4. VERTICAL MODE: CH1, CH2, DUAL, ADD
  5. VOLTS/DIV: Vertical sensitivity selector
  6. VARIABLE: Fine adjustment of vertical sensitivity
  7. POSITION: Vertical position control for both channels
  8. AC-GND-DC: Input coupling selector
  9. TIME/DIV: Time base selector
  10. TRIGGER SOURCE: CH1, CH2, LINE, EXT
  11. TRIGGER MODE: AUTO, NORM, TV-V, TV-H
  12. LEVEL: Trigger level adjustment

WARNING! High voltage present inside unit. Only qualified personnel should perform internal adjustments.

Rear Panel Connections

Rear panel connectors and their functions.

  1. Power cord receptacle
  2. Fuse holder (0.5A, 250V)
  3. Z-axis input connector
  4. Calibration output (2Vp-p, 1kHz square wave)
  5. CH1 output (buffered vertical signal)
  6. External trigger input

CAUTION! Ensure proper grounding and use correct fuse rating for safety.

Operating Instructions

Basic operation procedures for the CS 4125 oscilloscope.

  1. Power on: Allow 15 minutes warm-up for accurate measurements
  2. Connect probe to CH1 input and calibration output
  3. Set vertical mode to CH1, time base to 1ms/div
  4. Adjust intensity and focus for clear display
  5. Set trigger to AUTO mode for stable waveform
  6. Compensate probe using calibration signal
  7. Make voltage and time measurements using graticule

Tip: Always use properly compensated probes for accurate measurements.

Block Diagram

System block diagram showing major functional sections.

Circuit Description

Detailed description of major circuit sections and their operation.

Vertical Amplifier: Input protection, attenuator, pre-amplifier, and main vertical amplifier stages. Time Base: Trigger circuit, sweep generator, and horizontal amplifier. CRT Circuit: High voltage generator, focus and intensity controls. Power Supply: Transformer, rectifiers, and regulators for all required voltages.

Calibration Procedures

Step-by-step calibration procedures for maintaining accuracy.

  1. Warm up unit for 30 minutes before calibration
  2. Check and adjust DC balance
  3. Calibrate vertical sensitivity using known voltage source
  4. Adjust time base accuracy with frequency counter
  5. Check and adjust trigger sensitivity
  6. Verify CRT alignment and focus
  7. Perform final accuracy verification

WARNING! High voltage present. Use proper safety procedures.

Troubleshooting Guide

Common problems and their solutions.

SymptomPossible CauseCorrective Action
No displayPower supply failureCheck fuse, power supply voltages
Unstable triggerTrigger circuit faultCheck trigger components, clean switches
Inaccurate amplitudeVertical amp calibrationRecalibrate vertical sensitivity
Poor focusCRT circuitCheck focus voltage, CRT socket
No horizontal sweepTime base failureCheck sweep generator IC

Parts List

Complete list of components with part numbers and specifications.

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

  1. Power supply schematic
  2. Vertical amplifier (CH1 and CH2)
  3. Time base and trigger circuits
  4. Horizontal amplifier
  5. CRT and high voltage circuits
  6. Front panel control circuits

Note: Schematics show component values, test points, and voltage references.

Safety Precautions

Important safety information for service personnel.

FCC Part 15: Class A digital device; complies with interference limits for industrial use. Copyright © Kenwood Corporation. For service support, contact authorized Kenwood service centers only. High voltage warning: CRT anode voltage exceeds 10kV. Always discharge CRT before servicing. Use isolation transformer when servicing live circuits.

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