On 4 Feb 2006 10:23:41 -0800, "GT" wrote:

Bought in 1999 it is a microwave/oven unit.
I have checked the following parts & they have readings on my ohm
meter.
Door switch sensors, upper & lower. There are two separate sensors for
the bottom switch. They read totally different from each other
depending if door is open or shut.
HV Capacitor
Replaced Diode (connecting to capacitor) could not get a reading on ohm
meter & guy at parts store said this is normally why they stop heating.
Magnatron
Fan runs
Heating sensors (one on top of magnetron & other just inside unit)

Bad: Turntable motor, I took it out & it had an infinity reading.

Question what else is there to check to see why the microwave is not
cooking?
Thanks for any insight
Garry

Like Sam says, check the input to the primary of the transformer. If
you don't have line voltage there (when it should be running) nothing
will heat. If you don't have line voltage it means one of the safety
devices (over heat, fuse, interlock switches etc is open) or the
controller isn't calling for heating.

1999 means it probably has a micro processor controlled clock, timer,
heat modulating controller. Generally cheaply made, but reasonably
reliable.

How did it fail? Just quit or died over a period of time? Quit
suddenly - check the magnetron filament for an open (check the primary
to the HV transformer FIRST for line voltage). Keep your eyes open...
any evidence of lightning strikes? (clock and microwaves seem to be
the first to go)

If you can find that the controller isn't calling for heat when it
should be, then you might (if you have the skills to stay safe) bypass
the controller and see if it heats a cup of water.

Dying over a period of a year or two - probably a bad magnetron
(rarely a problem - but possible - with the cap or diode) That's
where current and voltage measuring come in handy.

I've fixed a few microwave ovens - it is frustrating having to deal
with symptoms when you can't actually check things (like current to
the magnetron or high voltage).

Most of the problems I've had are safety interlock problems (door
switches, or over temp fuses that opened because some food occluded
the mica window that lets the waves in), two controller problems (one
that I could fix - the other in a proprietary chip that was too
expensive)

Like Sam says - worry about your safety. My own practice is to keep
one hand in my pocket, my feet on an insulator, and one hand to work
the test probe. The very idea of discharging a cap in a microwave
give me the willies, and I worked on megawatt CW transmitters in the
Navy, and play with Tesla coils at home.
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