Electrical – What are these SMD components with 3 leads


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I am trying to repair a vacuum fluorescent display module by Futaba model code is M402SD07GS. It is seen that there is no energy on the display and Vcc and GND legs are short-circuited at "C1162" grid/anode driver.

When I look at the circuit to understand where the short circuit is, I am encountered these 3-lead components with very short codes on them.

Since I do not know what these components are, I cannot continue to understand where the short circuit is. I can not order because I do not know the product codes

When I look closely, the following is written on the components.

L G for Q1 
332 for ZD1
D3  for D2
D3  for D3
113 for ZD2 

Is there a way to figure out what this 3-legged component is?

Best Answer

The package is called "SOT-23" (small outline transistor), and it is used for all kinds of small-signal semiconductor devices, including BJTs, MOSFETs and diodes of all types (single and dual).

Since they are very tiny, only a small amount of information can be printed on them for identification. These tend to be manufacturer-specific strings of letters and digits, and tracing them back to a specific device is somewhat of a black art. There are websites that can help with this.

As Andy says, the reference designator on the board can offer some general clues about where to look.

  • D generally denotes a diode (or pair of diodes)
  • ZD would be a zener diode specifically
  • Q generally denotes a transistor (could be BJT or MOSFET)
  • M would generally be specifically a MOSFET
  • U might be some kind of integrated circut, such as a voltage reference or low-power regulator