6-
30
10V, 1 kΩ range
Figure 6-40. Signature of a SCR (C106B Type ) with the DC Source Test
Observe that as the test voltage increases to about 0.6 Volts, the SCR begins to turn on. Watch
the signature change from an open signature to a diode signature.
Applying What We Have Learned
• The Tracker 2700 can also dynamically test optocouplers and phototransistors. These
components are commonly found in isolation and switching circuits. Their operation can
slowly deteriorate making them intermittent. This type of problem is extremely difficult to
troubleshoot. With Tracker signature analysis, the Tracker 2700 will detect small amounts of
degradation in an optocoupler's LED and the phototransistor's emitter-collector junction.
• The SCR and TRIAC can also be a problem to troubleshoot. They may be used to switch
large currents. Quite often these components are susceptible to degradation and eventual
failure. The Tracker 2700 can easily show these failures.
Triacs are similar to SCRs and defective ones can be found in a similar fashion.
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