SCR Component Analyzer – A Preferred Test Methods
Posted on 15. Jul, 2011 by Admin in Datasheet, Electronics, Electronics Components
The term SCR stands for Silicon Controlled Rectifier. These three terminal devices can be tested by a number of different methods. The more common methods utilize a DVM (Digital Volt Meter) or an Analog Meter. Usually the SCR is tested by simply looking for the lack of conduction between Anode and Cathode leads. A high resistance would indicate a functional device, given the limitations of not gating the device.
Another method that is used in some Repair Centers involves a Test lamp, a battery and a few Test leads. The lamp and battery are connected in Series then placed across the SCR’s Anode and Cathode leads (the negative lead of the battery connects to the SCR’s Cathode lead). A flying test lead is then used to trigger the SCR by momentarily connecting the positive terminal of the battery to the SCR’s gate lead.
Both of these Test methods can provide an indication of device functionality when no other methods are available. Unfortunately, both methods require the Technician to consult a Datasheet or Service Manual prior to Testing the SCR. This ensures correct lead configuration. If the device pinout can not be determined, then the whole Test process becomes little more than a guess, or a hit-and-miss operation.
Failure analysis or Functional Test of the SCR should always be performed when the device is out of circuit. This means that the component should not be electrically connected to anything other than the Test Equipment that is used to evaluate the devices functionality.
At a well equipped Repair Center, SCR’s are tested utilizing an SCR Component Analyzer. This equipment confirms the SCR’s functionality, by gating the device and intelligently measuring its device characteristics. Confirm that the device tests as follows:
Press the Red Test Button to turn the Component Analyzer on. The Blue Result LED will light. Attach the Test Leads to the SCR’s Gate, Cathode and Anode Terminals. It is not important which leads go where. The Component Analyzer will determine the connection details.
Press the Red Test Button. The first three LED’s will display the connection details for a functional device. The Result LED will display the Test result. A Blue LED means that the device has an open circuit condition. A Red LED means that the device is shorted. A Green LED means that the device is Functional.
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 ampere. 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 it.
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 reading.
If you don’t have this tester for checking SCR, I’m showing 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 current. 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 etc.