Mastech MS8265, Operator'S Instruction Manual

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14

3.2.3 Diode Test

To avoid electrical shock and/or damage to the 
instrument, disconnect circuit power and 
discharge all high-voltage capacitors before 
testing diodes.

Use the diode test to check diodes, and other 
semi- conductor devices. The diode test sends a 
current through the semiconductor junction, and then 
measures the voltage drop across the junction; a 
good silicon junction drops between 0.5V and 0.8V.
To test a diode out of a circuit:
1.

Set the rotary switch to

range.

2. Connect the black and red test leads to the 

COM

and

terminals respectively.

3. For forward-bias readings on any semiconductor 

component, place the red test lead on the 

component's anode and place the black test lead 

on the component's cathode.

4. The meter will show the approx. forward voltage of 

the diode. If the test lead connection is reversed, 

only figure "1" displayed.

In a circuit, a good diode should still produce a forward 
bias reading of 0.5V to 0.8V; however, the reverse-bias 
reading can vary depending on the resistance of other 
pathways between the probe tips.

Resistance is an opposition to current flow.
The unit of resistance is the ohm ( ). 
The Meter's resistance ranges are 200.00

Ω

, 

2.0000k

Ω

, 20.000k

Ω

, 200.00k

Ω

, 2.0000M

Ω

, 

20.000M

Ω

 and 200.00M

Ω

.

To measure resistance:
1. Set the rotary switch to proper range.
2. Connect the black and red test leads to the COM 
    and 

terminals respectively.

3. Connect the test leads to the circuit being 
    measured and read the displayed value. 

Ω

Ω 

Some tips for measuring resistance:

•

The measured value of a resistor in a circuit is often 

different from the resistor's rated value. This is 

because the Meter's test current flows through all 

possible paths between the probe tips.

•

In order to ensure the best accuracy in measurement 

of low resistance, short the test leads before

  measurement and memory the test probe resistance 

in mind. This necessary to subtract for the resistance 

of the test leads.

The resistance function can produce enough voltage 

   to forward-bias silicon diode or transistor junctions, 
   causing them to conduct. To avoid this, do not use the 
   2M range for in-circuit resistance measurements.

•

•

On 20MΩ and 200MΩ ranges, the meter may take 

   a few seconds to stabilize reading. This is normal 
   for high resistance measuring.

•

When the input is not connected, i.e. at open circuit, 

the figure "1" will be displayed for the over

range 

   condition.