Testing SCR Secrets-How To Test And Check Silicon Controlled Rectifier
With Peak Electronic Tester And Analog Meter
Testing SCR (silicon controlled rectifier) can be done by using an analog multi meter
or specialize tester (such as the Peak electronic atlas component analyzer) designed to check semiconductor
devices easily. SCR can be found in many electronic circuits. Part numbers such as the FOR3G and MCR 100-6
were very common used in computer monitor.
Some called SCR as thyristor but in actual fact the
word thyristor should not be associated exclusively with the silicon controlled rectifier. It is in fact a
general name given to all four layer PNPN devices including the commonly used SCR. The diac, the Triac, and
the SCS are the other popular devices belonging to the family of thyristors.
SCR consists of three pin of Gate (G), Anode (A) and Cathode (C). In order to identify
the pin out, one must find it from semiconductor data book such the famous Philips ECG master semiconductor
replacement guide. The data book will list out the general specification of the SCR such as the volt and
If you want to know more details about a particular SCR, you can always try to search
from the internet. Usually the SCR manufacturers will provide the full datasheet for those who want
Once you know the pin outs of the G, A and C legs you can begin to test the SCR.
If you have the Peak electronic atlas component analyzer tester, what you need to do is to connect the three
small clips to each pin of the SCR (any part number will do).
The tester will begin to analyze the SCR and prompt you with the display such as
“Sensitive or low power thyristor” before it tells you the exact pin outs of G, A and C. After the first
test, the tester will eventually show you the answer at the LCD display. Red is Gate, Green is Cathode and
Blue is Anode.
It is a simple process and you will know the answer in less than 10 seconds. If there
is a problem in the SCR, the tester would not be able to show the results instead it shows a shorted
Make sure set to X1 ohms to test SCR
Showing the right way to check SCR
If you don’t have this tester for checking SCR, I’m going to show you another easy way
on how to test SCR fast. You need an analog meter set to X1 ohm. Place the red probe to the Cathode and black
probe to the Anode pin. At this time the meter doesn’t show any reading. Now gently move the black probe and
touch the Gate pin (the black probe still touching the Anode pin) and you will notice the meter’s pointer
will kick as shown at the picture (low resistance).
Removing the black probe from the GATE pin (the black probe still touching
the Anode pin) you would noticed that the resistance continues to be there (low resistance). This is due to
the conduction of SCR as the meter battery is usually able to supply current more than the holding
If at this stage you removed the black probe from the Anode pin and connect it back,
the pointer will dropped back to infinity (high resistance). If the SCR could hold the resistance then the
SCR is considered good. If it can’t hold then the SCR is faulty.
Conclusion- Practice testing SCR more often to see how’s the result like. Try some
different part numbers and power SCR-and if the resistance don’t hold using X1 ohm, you may try X10 ohm and