How to Check if a Power Transistor is Good or Bad?
3 Answers
Use a multimeter to measure whether the voltage is normal to determine if there is a fault. Below is relevant information about power transistors: 1. Normal voltage values for various power transistors: (1) IGBT temperature detection circuit-----Pin 15 of U4 voltage value: 0.5V (2) Cookware temperature detection circuit-------Pin 14 of U4 voltage value: 0.38V (3) Power supply high and low voltage protection circuit----Pin 16 of U4 voltage value: 2.52V (4) Zero-crossing detection circuit-------------Pin 18 of U4 voltage value: 0.38V 2. Function: Generally used in the final stage of a circuit to drive loads, the output current is relatively large. Due to manufacturing process limitations, the amplification factor of high-current transistors is not very large, so composite transistors are used to increase the amplification factor. The transistor that serves as the final output in an amplification circuit is called a power transistor. Power transistors are divided into high-power transistors and low-power transistors. Generally, those with a PCM (collector power dissipation) greater than 1W are called high-power transistors, such as domestic 3DD and 3DA types and Japanese 2SD and 2SC transistors. Those with a PCM less than 1W are called low-power transistors, such as 3AX and 3DG types. Some better circuits use CMOS field-effect transistors as power amplification transistors.
Automotive power transistors, also known as high-power transistors, are quite common in engines or ignition systems. Last time my car wouldn't start, I suspected it was faulty. The first step in checking is to disconnect the negative terminal of the battery to avoid short-circuit hazards. Then use a multimeter to test: set it to the diode test or resistance mode, locate the three pins of the power transistor. Normally, when the red probe is connected to the base and the black probe to the collector, it should conduct with relatively low resistance. If the multimeter shows infinity or an extremely low value, it may indicate an internal short circuit or open circuit. You can also visually inspect it for signs of burning or cracks. If the test results are abnormal, it's likely faulty, and it's best to replace it with a new one. If you're still unsure, take it to a repair shop for a professional diagnosis with specialized tools. While driving, pay attention to engine misfires or ignition issues to avoid breakdowns on the road.
I've been driving for over a decade and encountered power transistor failures multiple times. This component works inside the control module, and checking its condition is quite straightforward: After disconnecting the battery, use a multimeter's resistance setting to measure values between the pins. Typically, place the red probe on the base and the black probe on the emitter or collector; normal readings should be between tens to hundreds of ohms. If the reading shows zero or infinite resistance, it means the transistor is burnt out. Alternatively, switch the probe positions during testing—if both ends show the same resistance value, there might be an internal short circuit. Also, check the transistor's exterior for any bulging or discoloration. If you're unsure about your measurements, don't force it to avoid damaging the entire circuit. Spending a few hundred bucks at a repair shop is quicker and safer. Remember, a faulty power transistor often causes ignition failure and should be repaired promptly.
