Mastech M92AH Digital Multimeter User Manual

1. Introduction

This manual provides detailed instructions for the safe and effective operation of your Mastech M92AH Digital Multimeter. This device is designed for measuring AC/DC voltage, AC/DC current, resistance, diode testing, hFE testing, and continuity checking. Please read this manual thoroughly before use and retain it for future reference.

2. Safety Information

CAUTION: To prevent potential damage to the multimeter or personal injury, observe the following safety guidelines:

• Never attempt to measure AC voltage while the multimeter is set to DC mode. This will damage the meter.
• Always ensure the test leads are correctly connected to the appropriate input jacks for the measurement being performed.
• Do not exceed the maximum input values for any range.
• Exercise extreme caution when working with live circuits.
• Before changing functions, disconnect the test leads from the circuit under test.
• Replace the battery when the low battery indicator appears to ensure accurate readings.

3. Product Overview

The Mastech M92AH Digital Multimeter is a portable, battery-powered device designed for various electrical measurements.

Figure 1: Mastech M92AH Digital Multimeter. This image displays the Mastech M92AH Digital Multimeter, featuring a green protective casing and a black front panel. Key components visible include the LCD display at the top, a central rotary switch for selecting measurement functions, and three input jacks (10A, COM, VΩmA) at the bottom for connecting test leads. The power button and "AUTO POWER OFF" indicator are also visible near the display.

3.1 Components

• LCD Display: 1999 counts display for measurement readings. Includes indicators for low battery and data hold.
• Rotary Switch: Used to select the desired measurement function (e.g., V~, V-, A~, A-, Ω, Diode, hFE, Continuity).
• Input Jacks:
  • "COM" Jack: Common (negative) input for all measurements.
  • "VΩmA" Jack: Positive input for voltage, resistance, and current measurements up to 200mA.
  • "10A" Jack: Positive input for high current measurements (up to 10A).
• Power Button: Turns the multimeter ON/OFF.
• Data Hold Button: Freezes the current reading on the display.

4. Setup

4.1 Battery Installation

1. Ensure the multimeter is turned OFF and disconnect all test leads.
2. Locate the battery compartment cover on the back of the unit.
3. Unscrew the retaining screw(s) and remove the cover.
4. Insert a new 9V battery, observing correct polarity (+ and -).
5. Replace the battery compartment cover and secure it with the screw(s).

4.2 Connecting Test Leads

• Always connect the black test lead to the "COM" jack.
• For voltage, resistance, diode, hFE, continuity, and current measurements up to 200mA, connect the red test lead to the "VΩmA" jack.
• For current measurements between 200mA and 10A, connect the red test lead to the "10A" jack.

5. Operating Instructions

5.1 Power ON/OFF and Auto Power Off

• Press the "ON/OFF" button to turn the multimeter on.
• The multimeter features an auto power-off function to conserve battery life. It will automatically turn off after approximately 15 minutes of inactivity.
• To disable auto power-off (for continuous use), hold down the "DATA HOLD" button while turning the meter on.

5.2 Measuring DC Voltage (V-)

1. Connect the black lead to "COM" and the red lead to "VΩmA".
2. Set the rotary switch to the desired DC Voltage range (e.g., 200mV, 2V, 20V, 200V, 1000V). Select a range higher than the expected voltage.
3. Connect the test leads across the component or circuit to be measured.
4. Read the voltage value on the LCD display.

5.3 Measuring AC Voltage (V~)

1. Connect the black lead to "COM" and the red lead to "VΩmA".
2. Set the rotary switch to the desired AC Voltage range (e.g., 200V, 700V). Select a range higher than the expected voltage.
3. Connect the test leads across the component or circuit to be measured.
4. Read the voltage value on the LCD display.

5.4 Measuring DC Current (A-)

1. IMPORTANT: Ensure the circuit is de-energized before connecting the multimeter in series.
2. Connect the black lead to "COM".
3. For currents up to 200mA, connect the red lead to "VΩmA". For currents up to 10A, connect the red lead to "10A".
4. Set the rotary switch to the appropriate DC Current range (e.g., 20uA, 2mA, 20mA, 200mA, 10A).
5. Open the circuit where current is to be measured and connect the multimeter in series.
6. Apply power to the circuit and read the current value on the LCD display.

5.5 Measuring AC Current (A~)

1. IMPORTANT: Ensure the circuit is de-energized before connecting the multimeter in series.
2. Connect the black lead to "COM".
3. For currents up to 200mA, connect the red lead to "VΩmA". For currents up to 10A, connect the red lead to "10A".
4. Set the rotary switch to the appropriate AC Current range (e.g., 20uA, 2mA, 20mA, 200mA, 10A).
5. Open the circuit where current is to be measured and connect the multimeter in series.
6. Apply power to the circuit and read the current value on the LCD display.

5.6 Measuring Resistance (Ω)

1. IMPORTANT: Ensure the circuit or component is de-energized before measuring resistance.
2. Connect the black lead to "COM" and the red lead to "VΩmA".
3. Set the rotary switch to the desired Resistance range (e.g., 200Ω, 2kΩ, 20kΩ, 200kΩ, 2MΩ, 20MΩ, 200MΩ).
4. Connect the test leads across the component to be measured.
5. Read the resistance value on the LCD display.

5.7 Diode Test

1. Connect the black lead to "COM" and the red lead to "VΩmA".
2. Set the rotary switch to the Diode symbol.
3. Connect the red lead to the anode and the black lead to the cathode of the diode. A forward voltage drop (typically 0.5V to 0.8V) will be displayed.
4. Reverse the leads. The display should show "OL" (Open Loop) for a good diode.

5.8 hFE Test (Transistor Test)

1. Set the rotary switch to the hFE position.
2. Identify if the transistor is NPN or PNP.
3. Insert the transistor leads (Emitter, Base, Collector) into the corresponding sockets in the hFE test slot.
4. The display will show the hFE value (DC current gain) of the transistor.

5.9 Continuity Check

1. Connect the black lead to "COM" and the red lead to "VΩmA".
2. Set the rotary switch to the Continuity symbol (often shared with Diode test, indicated by a buzzer icon).
3. Connect the test leads across the circuit or component.
4. If continuity exists (resistance below a certain threshold), the buzzer will sound, and the display will show a low resistance value. If no continuity, "OL" will be displayed.

5.10 Data Hold

• Press the "DATA HOLD" button to freeze the current reading on the display.
• Press the button again to release the hold and resume live readings.

6. Maintenance

6.1 Battery Replacement

When the low battery indicator appears on the display, replace the 9V battery as described in the "Battery Installation" section (4.1).

6.2 Cleaning

Wipe the case with a damp cloth and mild detergent. Do not use abrasives or solvents.

6.3 Fuse Replacement

If the current measurement function fails, the fuse may need replacement. This procedure should only be performed by qualified personnel. Refer to the specifications for the correct fuse type.

7. Troubleshooting

8. Specifications

9. Warranty and Support

For warranty information and technical support, please refer to the documentation provided with your purchase or contact Mastech customer service. Keep your purchase receipt as proof of purchase.