You Can Fix Any Microwave Oven with This FREE, Common Sense Troubleshooting Guide for Diagnosing and Repairing Commercial and Residential Microwave Oven Problems

© 1989-2013 J. Carlton Gallawa All Rights Reserved Worldwide

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(Updated 10/19/2013)
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Important Safety Information for Repairing Microwave Ovens

Repairing a microwave oven is a very dangerous task. To avoid personal injury or death, please read, understand and follow these very IMPORTANT SAFETY PRECAUTIONS as well as our TERMS OF USE and DISCLAIMER at the bottom of this page BEFORE proceeding with any tests or troubleshooting 

The following troubleshooting flow chart provides a comprehensive selection of symptoms, problems, failures and fixes that can occur in both commercial and residential models of microwave ovens.

When troubleshooting an oven, identify the symptom as accurately as possible and refer to the following chart for tips and guidelines. Please note that symptoms, causes and remedies are listed in logical order and probability of occurrence, starting with general categories of the most common complaints.

When diagnosing the microwave oven, it is best to follow the sequence of checks without skipping any steps, progressively narrowing down the likely causes until only the real culprit remains.

Many of the possible causes will require that a specific test be performed, a link will take you to that procedure.

Commercial Microwave Oven OEM Parts
If you are unsure or uncomfortable about a procedure, test or any other aspect of this Site, please STOP and call a qualified professional technician.
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General Symptoms

Specific Symptoms Cause and Corrective Action  

Heating or Cooking Problems

Oven runs, but does not heat at all Shorted high-voltage (HV) diode - TEST  Click to look inside or purchase at Amazon.com
Shorted HV transformer - TEST
Shorted magnetron - TEST
Magnetron dome (or antenna) damaged from arcing (if this is the case, check for a stalled stirrer/antenna) INSPECT/FIX
Magnetron insulator breakdown INSPECT/FIX
Short in the HV wiring - Visually inspect
Shorted HV capacitor (this will usually cause the fuse to blow within seconds after cook cycle is started) - TEST

Open HV diode - TEST
Open magnetron filament - TEST
Intermittent or oxidized connection to one or both magnetron filament terminals - INSPECT/FIX
Open HV transformer (usually the primary winding) - TEST
Defective interlock switch - TEST
Burned slip-on connector to interlock switch. INSPECT and repair as necessary.
Defective triac - TEST
Open fuse in HV circuit (more common in commercial models)
Open HV capacitor (uncommon) TEST
Weak (low) heat

How to safely measure the outlet (line) voltage

In any of the following cases, the magnetron is failing and should be replaced:

Intermittent heat Intermittent or oxidized/burned connection to one or both magnetron filament terminals - INSPECT/FIX
INSPECT for a a burned slip-on connector due to a poor crimp joint, or weakened connection. Repair or replace as necessary.
Uneven heat (hot spots) Check for mechanical bind, loose terminal connection or open motor windings (test procedure coming soon)
Starts cooking by itself / Only cooks at full power Defective triac - TEST

Electric Power Problems Completely dead (as though unplugged)  
Goes dead intermittently  
Goes dead in mid-cycle (overheats) Check for mechanical bind, loose terminal connection or open motor windings (test procedure coming soon)
Inspect - Clean as necessary
Inspect - Correct as necessary

Timer, Control Panel or Feature Problem Timing problem Check for mechanical bind, loose terminal connection or open motor windings (test procedure coming soon)  
Control or programming problem Defective touch panel (keypad). NOTE: If none of the pads respond, the problem could be elsewhere. More info to come.
Display Problem Defective control board (main printed circuit board)
  Defective control board (main printed circuit board) or sensor unit

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USE OF THIS SITE : Through your use of this Site, you certify that you have read, understood and agreed to the following TERMS OF USE, including the following disclaimer as well as these safety precautions.

TERMS OF USE: Through your use of this Site, you hereby acknowledge and agree that troubleshooting and repairing a microwave oven can be dangerous and can involve risk of serious injury and/or death and/or property damage. Further, you consciously and voluntarily assume all such risks, dangers and hazards inherent in these procedures and assume the same risks for any invitees including minor children or legal wards.

DISCLAIMER: The author and/or owner and/or administrator of this Site assumes no liability for any incidental, consequential or other liability from the use of this information. All risks and damages, incidental or otherwise, arising from the use or misuse of the information contained herein are entirely the responsibility of the user. Although careful precaution has been taken in the preparation of this material, we assume no responsibility for omissions or errors.

Copyright © Information: Unless otherwise noted, all materials at this cite (including without limitation all text, HTML markup, graphics, and graphic elements) are copyrighted © 1989-2013 by J. Carlton Gallawa. The material available through this site may be freely used for attributed noncommercial educational purposes only. We ask that due credit and notification be given the author. All materials appearing on this Web site may not be reproduced, stored in any retrieval system, or used in any way for commercial purposes without the express prior written permission of the copyright holder. Send correspondence to: Microtech, P.O. Box 940, Gonzalez, Florida 32560

© 1989-2013 J. Carlton Gallawa . All Rights Reserved Worldwide

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