How To Test Adjustable Precision Shunt Regulator TL431
If you repair the SMPS that have the optoisolator IC connected between the primary and the secondary section, you would usually see a transistor like component. It is actually the TL431 IC adjustable precision shunt regulator and it just like the shape of a C945 transistor. How am i going to test it?
Simple-Set your analog meter to X 10 K ohm range. Black probe to pin1 and red probe to pin 2 and 3 (must have readings) then black probe to pin 2 and red probe to pin 1 and 3 (must have readings). If black probe to pin 3 and red probe to pin 1 and 2-it should have no reading. If there is a reading then it is consider shorted. How acurate is this test? It is 90 over percent and this case is quite similar to my previous post about testing the PWM UC3842 IC. That means, if you still suspicious about the reading then the only way is to direct replace the component and retest the smps again. This component is quite cheap and easily get from those used electronic board especially the SMPS that have the optoisolator in it.
What happen to the power supply if this component is shorted or leaked? It would cause power blink/cycling, low power or even intermittent no power problem.