• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

    Jake
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Sharp Microwave R-120DB No Heat

banamber

Premium Member
Joined
Jul 10, 2021
Messages
7
Location
Northeast, USA
Model Number
R-120DB
Brand
Sharp
Age
More than 10 years
My spare microwave is a Sharp R-120DB. The other day I got it out. I heated up a hotdog in it and it worked fine. After that it wouldn't heat anymore. I checked the interlock switches, they're all working. The thermal cutout is closed. C/T fuse is closed. Rectifier diode looks fine. I haven't done any testing on the HV parts yet (Including the rectifier). While this microwave is old (Manufactured in 2000), it doesn't have many hours on it since it was always sitting around as a spare.

The top of the machine, around where the magnetron and HV cap are does get warm after running for a minute.

I also hooked it up to my Kill-A-Watt Meter. It's only drawing 2.99 amps and 310 watts. According to the manual, it should be drawing about 9 amps (1030 watts). Does this indicate the rectifier diode has failed?
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
43,740
Location
Murray, Utah 84107, United States
Check for 120 VAC on the primary side of the transformer. If the voltage is correct, thee problem is one of the HV components:
C-HV Testing big.jpg
 

banamber

Premium Member
Joined
Jul 10, 2021
Messages
7
Location
Northeast, USA
Thanks for the tip. I haven't tried testing for 120v to the transformer yet, but I just did all the other tests in the image, and it appears everything tests fine. Across the transformer primary 0.6 ohms, filaments about 0.6 ohms, secondary to ground 160 ohms. Again about 0.6ohms across the mag. Cap across terminals megaohms to infinite, terminals to body open. Rectifier closed one way, open the other way. I also tested the primary interlock relay which is indicated for this condition in the troubleshooting section and that also tests fine.

I'll give the voltage test a shot once I get this thing back together, but it's so strange that everything seems to test fine, yet it won't heat.
 

banamber

Premium Member
Joined
Jul 10, 2021
Messages
7
Location
Northeast, USA
I had just realized when I tested the magnetron I just did a beep test for terminal to chassis. So I just checked the resistance from terminal to case and I'm getting 300-some ohms on both terminals. Is this a problem?
 
Last edited:

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
43,740
Location
Murray, Utah 84107, United States
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