Mastech MS850D Digital Multimeter Instruction Manual

1. Introduction

Thank you for choosing the Mastech MS850D Digital Multimeter. This device is a true-RMS, auto-ranging digital multimeter designed for safe and accurate troubleshooting of a variety of electrical problems in automotive and household settings. It features a large digital display, a flashlight, and various measurement functions including AC/DC voltage, AC/DC current, resistance, capacitance, frequency, duty cycle, temperature, diode, continuity, and non-contact voltage (NCV) detection.

Figure 1: Front view of the MS850D Digital Multimeter

2. Safety Information

To ensure safe operation and service of the meter, follow these safety guidelines:

• Always ensure the meter is in good working condition before use.
• Do not apply more than the rated voltage, as marked on the meter, between terminals or between any terminal and earth ground.
• Use caution when working with voltages above 30V AC RMS, 42V peak, or 60V DC. These voltages pose a shock hazard.
• Always disconnect the test leads from the circuit before changing functions or ranges.
• Do not use the meter if the test leads are damaged or if the meter itself appears damaged.
• Ensure the battery cover is securely closed before operating the meter.
• Observe all local and national safety codes.
• The meter is rated for CAT III 600V.

3. Product Overview

The Mastech MS850D features a robust design with a clear digital display and intuitive controls.

3.1. Components and Controls

Figure 2: Angled front view of the MS850D

The multimeter includes:

• Digital Display: Large, easy-to-read display for measurement results.
• Rotary Function Switch: Used to select the desired measurement function (e.g., V~, V-, A~, A-, Ω, Hz, °C/°F, NCV).
• Function Buttons:
• SEL (Select): Toggles between different measurement modes within a single rotary switch position (e.g., AC/DC voltage, resistance/continuity/diode).
• HOLD: Freezes the current display reading.
• O/H (Backlight/Flashlight): Activates the display backlight and the integrated flashlight.
• MIN/MAX/REL: Cycles through minimum, maximum, and relative measurement modes.
• Input Jacks:
• 10A MAX: For high current measurements (up to 10A).
• COM: Common terminal for all measurements.
• VΩmA: For voltage, resistance, capacitance, frequency, duty cycle, temperature, and low current measurements.
• Flashlight: Located at the top of the device for illuminating work areas.
• Kickstand: Integrated on the back for hands-free operation.

Figure 3: Back view of the MS850D

Figure 4: MS850D with kickstand extended

3.2. Product Demonstration Video

4. Setup

4.1. Battery Installation

The Mastech MS850D requires two 1.5V AAA batteries (not included). To install or replace batteries:

1. Ensure the multimeter is turned OFF.
2. Locate the battery compartment on the back of the meter.
3. Unscrew the battery cover and remove it.
4. Insert two 1.5V AAA batteries, observing the correct polarity (+ and -).
5. Replace the battery cover and secure it with the screw.

4.2. Connecting Test Leads

Always connect the black test lead to the 'COM' (Common) jack. Connect the red test lead to the appropriate input jack based on the measurement you intend to make:

• For Voltage, Resistance, Capacitance, Frequency, Duty Cycle, and Temperature measurements, connect the red lead to the 'VΩmA' jack.
• For Current measurements (up to 600mA), connect the red lead to the 'VΩmA' jack.
• For High Current measurements (up to 10A), connect the red lead to the '10A MAX' jack.

5. Operating Instructions

Turn the rotary switch to the desired function. Use the 'SEL' button to toggle between modes if multiple functions share a single switch position.

5.1. Voltage Measurement (AC/DC)

1. Set the rotary switch to 'V~' for AC Voltage or 'V-' for DC Voltage. The meter is auto-ranging.
2. Connect the test leads in parallel to the circuit or component to be measured.
3. Read the voltage value on the display.

5.2. Current Measurement (AC/DC)

1. Set the rotary switch to 'A~' for AC Current or 'A-' for DC Current.
2. For currents up to 600mA, connect the red lead to the 'VΩmA' jack. For currents up to 10A, connect the red lead to the '10A MAX' jack.
3. Connect the test leads in series with the circuit.
4. Read the current value on the display.

5.3. Resistance Measurement

1. Set the rotary switch to 'Ω'.
2. Connect the test leads across the component to be measured.
3. Read the resistance value on the display.

5.4. Capacitance Measurement

1. Set the rotary switch to 'Hz/%/°C/°F' and press 'SEL' until 'nF' or 'uF' is displayed.
2. Connect the test leads across the capacitor.
3. Read the capacitance value on the display.

5.5. Frequency and Duty Cycle Measurement

1. Set the rotary switch to 'Hz/%/°C/°F' and press 'SEL' until 'Hz' or '%' is displayed.
2. Connect the test leads to the signal source.
3. Read the frequency or duty cycle value on the display.

5.6. Temperature Measurement

1. Set the rotary switch to 'Hz/%/°C/°F' and press 'SEL' until '°C' or '°F' is displayed.
2. Connect the temperature probe to the 'VΩmA' and 'COM' jacks.
3. Place the probe on or in the object whose temperature is to be measured.
4. Read the temperature value on the display.

5.7. Diode and Continuity Test

1. Set the rotary switch to 'Ω' and press 'SEL' to cycle to diode or continuity mode.
2. For diode test, connect the red lead to the anode and black lead to the cathode.
3. For continuity test, connect the leads across the circuit. A buzzer will sound for continuity.

5.8. Non-Contact Voltage (NCV) / Live Wire Recognition

1. Set the rotary switch to 'Live NCV'.
2. Hold the top of the meter near a live AC voltage source. The meter will indicate the presence of voltage without direct contact.

5.9. Special Functions

• Auto Power Off: The meter will automatically turn off after a period of inactivity to save battery life.
• Data Hold: Press the 'HOLD' button to freeze the current reading on the display. Press again to release.
• MAX/MIN: Press 'MIN/MAX/REL' to record and display the maximum or minimum reading.
• REL (Relative Measurement): Press 'MIN/MAX/REL' to enter relative mode, displaying the difference between the current reading and a stored reference value.
• Flashlight: Press and hold the 'O/H' button to turn on the flashlight.

6. Specifications

The following table details the technical specifications of the Mastech MS850D Digital Multimeter:

Figure 5: Detailed Specifications and Features

6.1. General Specifications

7. Maintenance

7.1. Cleaning

Wipe the meter with a dry, clean cloth. Do not use abrasives or solvents. If necessary, a damp cloth with mild detergent can be used, followed by a dry cloth.

7.2. Battery Replacement

When the battery indicator appears on the display, replace the batteries as described in the 'Battery Installation' section (4.1). Always use two fresh 1.5V AAA batteries.

7.3. Fuse Replacement

If the current measurement function fails, the fuse may need replacement. Refer to the warning label on the back of the device for fuse specifications (e.g., F300mA/250V and F10A/250V). Fuse replacement should only be performed by qualified personnel.

8. Troubleshooting

If you encounter issues with your Mastech MS850D, consider the following common troubleshooting steps:

• No display or dim display: Check battery installation and replace batteries if necessary.
• Incorrect readings: Ensure test leads are properly connected to the correct jacks and the rotary switch is set to the appropriate function. Verify the component being tested is functioning correctly.
• No continuity beep: Check if the circuit is truly continuous. Ensure the meter is in continuity mode.
• NCV not detecting voltage: Ensure the meter is in NCV mode and held close enough to the live wire.
• Meter does not turn on: Check batteries. If the issue persists, contact support.

9. User Tips

• Always start with the highest range when measuring an unknown voltage or current to prevent overloading the meter.
• For stable readings, ensure good contact between the test probes and the circuit points.
• The auto-ranging feature simplifies operation, but understanding the manual ranges can be beneficial for specific applications.
• Utilize the kickstand for hands-free operation, especially when working on a bench.
• The flashlight is useful for working in dimly lit environments.

10. Warranty and Support

For warranty information or technical support, please refer to the documentation provided with your purchase or contact the manufacturer directly. Keep your proof of purchase for any warranty claims.