Excerpts from the book The Complete Microwave Oven Service Handbook
--NOW available on CD-ROM (CLICK HERE)
and from the video You Can Fix Microwave Ovens
Copyright © 1998-2006 by J. Carlton Gallawa
© 1996-2006 J. Carlton Gallawa . All Rights Reserved Worldwide
| Low voltage transformers, also referred to as control transformers, serve to step down the line voltage to low voltages that supply power to the electronic control circuitry. These transformers usually have several secondary outputs, which provide an appropriate selection of control voltages as required by the various control components. | |
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In the numerous different models that use a low voltage transformer, the mounting and structure of the transformer can vary considerably. In some cases, it is mounted on the base of the oven. In many models, it is soldered into the printed circuit board, and some models use a transmotor. This is a combination blower motor and low voltage transformer with a secondary winding that provides stepped down voltages. For test purposes, we will use the generic transformer pictured below. A general resistance check of the low voltage transformer can be performed as follows. |
Measuring from any terminal on the primary side to any terminal on the secondary side should produce a reading of infinity. The same is true when measuring from either primary terminal to chassis ground.
An operational test may be made using the typical secondary voltages noted in the illustration as an approximate guide. However, it is unlikely that the configuration of any one transformer will correspond exactly to the voltages in this generic example.
USE EXTREME CAUTION DURING LIVE TESTS! DANGEROUSLY HIGH VOLTAGES ARE PRESENT DURING OVEN OPERATION. DO NOT TOUCH ANY COMPONENTS OR WIRING DURING A COOK CYCLE.
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