How To Test A Hockey Puck Diode Using A Standard Digital Multimeter


Welcome to G-TV! Today I’m going to show
you how to test a diode using a standard digital multi-meter. Safe and accurate testing of
a diode requires the device to be out of circuit. The type of diode I am testing today is commonly
called a hockey puck diode. A diode is like an electronic switch. It can be turned on
when rated voltage is applied, commonly around 0.6 Volts for a silicon diode, and it allows
current to flow in one direction and blocks current from flowing in the opposite direction.
When checking the condition of a diode or transistor junction, a multi-meter is the
preferred instrument versus an analog Volt-Ohm Meter or VOM. The VOM can give widely varying
readings and can drive undesirable currents levels of up to 50 milliamps through the junction.
Many brands of digital multi-meters have models that include a diode test function. Today
I will be using a Fluke 233. I will turn on the multi meter by setting the dial to the
diode test function indicated by the yellow diode symbol here. On the Fluke 233 you will
notice the white symbol here is for capacitance and not diode testing. Since the symbol is
yellow, I will push the yellow button here to change the setting of the multi-meter from
capacitance to diode testing. This diode test function will send a current through the semiconductor
junction and then measure the voltage drop across the junction. A good silicon junction
drops between 0.5 Volts and 0.8 Volts. For this hockey puck style diode the polarity
is determined by the diode symbol on the diode itself. Other hockey puck style diodes may
have a flange end. In this case, the cathode is on the side of the puck with the flanged
end. A hockey puck diode will often require clamping or compression in order to conduct
this test. This is because the actual silicon device is sandwiched in-between the metal
discs that make up the conductor surfaces, or pole faces of the diode. There is no mechanical
bond connecting the silicon device to the discs. The compression force required for
the device when installed in the actual application is usually stated in the manufacturers’
specifications. For the purpose of doing this static test, a minimal amount of clamping
force will usually suffice. My clamping rig consists of a hold down toggle clamp, a couple
flat metal, and fiberglass plates. The flat metal plates are being used to keep the force
of the clamp even across the pole faces and prevent the clamp from creating undesirable
marring or denting the pole face surfaces. Do not compress the disc more than the compression
limits of the diode. The fiberglass plates will insure that the poles of the diode are
not shorted by some conductive path in the test jig. Now that my diode is ready I will
plug in my leads. The red probe should be plugged into the appropriate positive test
terminal on the multi-meter and the black probe should be plugged into the common terminal.
Now I will place the positive probe on the anode and the negative probe on the cathode.
In this case, I’m looking for a voltage drop of about point 4, and I am listening for a
short beep. This reading indicates that the diode has passed this portion of the test.
Now if I were to see an open or short circuit, then this would indicate a bad diode. An open
diode appears on the multi-meter with the same indication you would have with the probes
not touching anything. The O L on the display indicates Open Leads or no continuity. A shorted
diode appears on the multi-meter with the same indication you would have with the probes
contacting each other directly. The point zero zero zero on the display and long continuous
beep indicates a zero voltage drop. A shorted or open diode clearly indicates that the diode
is bad. For the second test, I’m going to reverse my leads. I will place the positive
probe on the cathode and the negative probe on the anode. I should get an open reading
indicated by an O L on the display, like this. This reading indicates that the diode has
passed the second part of the test. Any other reading, indicating a voltage drop or short,
would reveal that the diode is bad. Static testing of a diode using a DMM is limited
and the only certain test results are open or short, which indicate the device is certainly
bad. Passing results may not accurately determine that a diode is actually good. The DMM is
most likely not able to simulate the application conditions, such as current load or voltage
levels. A diode that fails in the actual application environment may very well pass these limited
DMM static tests. Regardless of these limitations, static tests like these are very helpful during
the process of troubleshooting electronic circuits. Diodes and multi-meters such as
the Fluke 233 along with thousands of other products and services are available at galco.com

6 thoughts on “How To Test A Hockey Puck Diode Using A Standard Digital Multimeter

  1. Can I test the SCR(P480CH Series) with this multi-meter's diode function? Between the Gate and Cathode? thank you.

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