Appliance Tech Tips – Whirlpool Microwave High Voltage Transformer

Appliance Tech Tips
November 2016

Courtesy of Fred’s Appliance Academy

DISCLAIMER: Due the danger and complexity of electronics repair, the following shared technical tips are intended for professional reference only. Please refer to manufacturer’s recommendations as Encompass and Fred’s Appliance Academy do not guarantee the accuracy, reliability or safety of this information.
Electrical Shock Hazard: Disconnect power before servicing.
Replace all parts and panels before operating. Failure to do so can result in death or electrical shock.

One of our field techs brought us an Over-the-Range microwave transformer that had an open primary winding (120vac side). Keep in mind, a transformer is not a likely component to fail in a microwave, but it can on VERY rare occasions (typical issues on the high voltage side are usually Magnetron, HV Diode, and/or Capacitor).

After checking the transformer (see below for how to properly check a microwave transformer), we came to find out that the transformer winding for the low voltage primary winding (the 120vac connection tabs) have a varnish on them that will cause the meter to not see the 120vac present at the input. Second, we found after scraping the coating away that the windings themselves are aluminum, not copper.

Whirlpool Microwave HIgh Voltage Transformer

With that said, the soldering joints for the connections of the low voltage primary winding are not holding, which is causing the transformer to look as though the primary winding is open. You will still have to replace the transformer, and we suggest you check the new one as well before pulling the unit off the wall and installing a defective part for nothing. Never try to fix a soldering joint or broken wire on the transformer itself as this poses a danger to not only you as a tech, but to the customer with the possibility that the unit may catch fire.

The transformer was found in a Whirlpool microwave; the part number is W10836753.  Since the same design is used for multiple model numbers and brand names (Maytag, Amana, etc.), we recommend referencing the part number to determine if the transformer you are working on might have the same issue. We expect that this was not an isolated incident, so save yourself the time and hassle and check the transformer before ordering other replacement parts.

To diagnose the working status of a transformer on a Whirlpool OTR Microwave:

• Start by pulling unit down from wall
• Primary winding should have less than 5 ohms
  • No continuity from primary winding to ground
• High voltage secondary should have 35 to 150 ohms
  • Check from high voltage tab to ground
• Low voltage secondary should have less than one ohm
• If either transformer winding has failed, ohms will be way off

Special thanks to Fred’s Appliance Academy
academy.fredsappliance.com