Page 84 - Testing Electronic Components

Switch mode power transformer rarely breakdown and if it breakdown it
will usually cause power section components to blow or totally blow up
the main fuse and trip the ELCB (Earth Leakage Circuit Breaker). If a
SMPT failed, normally it was the primary winding shorted. The
secondary windings are very robust and seldom have problem.

In order to accurately test the primary winding, one cannot use the
multimeter resistance (Ohm) test as it was not accurate and will give a
false reading. In other words, a shorted primary winding will test good
with ohmmeter but failed when test with coil tester. The famous coil
tester is the Dick smith flyback tester. You can build the flyback tester by
visiting this website http://www.flippers.com/pdfs/k7205.pdf. Study the
manual and you will definitely know more about coil measurement and
other useful information.

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