From: John De Armond
Subject: Re: Microwave broken
Date: Mon, 25 Oct 1999 22:21:18 EDT
Chris Bryant wrote:
> On Sat, 23 Oct 1999 18:29:15 -0700, Michael Chang
> <email@example.com> wrote:
> >For someone handy, the URL I suggested contains more than
> >enough information to repair simple problems. The trouble
> >with $100 microwaves, is the poor quality construction and
> >marginal components used; one is likely to be very
> >disappointed. Microwave ovens are one of the simplest
> >appliances to repair. Complex parts such as the
> >timer/electronics assembly almost never goes wrong, and
> >common faults such as (door) micro switches, diodes, fuses,
> >thermal switches, even the magnetron, can be readily
> >replaced at relatively little cost.
I have at any one time 15-20 microwaves in use in my restaurant and
catering operation. Most are literally in continuous use throughout
the business day. Mean time to first failure of a new microwave is
about 9 months. In other words, I see and fix more microwaves in a
year than many repairmen do in a career.
That said, I'm an enthusiastic supporter of home microwave repair.
My experience is that about 90% of the failures not caused by abuse
involve microswitches, followed closely by the electronics module.
The major problem with the electronics module is that somehow some
obscure engineer seems to think it is proper to conduct 12-15 amps
through a printed circuit board trace and thin relay pin. The trace
gets hot, the solder joint becomes cold and smoke follows. The
board is usually trashed from the heat by the time the relay quits
working. That and the sensitivity of the electronics to surges
(electronic microwaves and generators do not like each other) leads
to my standard remedy - the installation of a standard spring-wound
30 minute timer through a hole drilled in the electronics panel.
This is the kind of timer used on attic fans and the like.
For the microswitches, one can pay $15 ea from the appliance parts
place or one can order them in bulk from DigiKey for about a buck a
Probably the biggest problem we see from continuous use is thermal
tripping (blowing those bullet thermal fuses) and wear on the
interlock causing the crowbar microswitch to short the line and blow
the internal line fuse. The interlock, required by law, contains 3
switches - one switch sends a door-open signal to the
microprocessor, one opens the line and the third crowbars (shorts)
the power leads to the magnetron. If the crowbar switch activates
before the line switch opens, the line fuse gets blown. There is a
range of adjustment on the latch or (I know this is controversal
with some) just toss the crowbar switch.
800-1000 watt magnetrons currently cost about $60 wholesale.
Pushing the limit of practicality for fixing old ovens that probably
also have other mechanical or cosmetic problems. I've never actually
bought a magnetron - used ones are easy enough to find.
> Plus- my poor wife is still using our 15 year old Amana Radar
> range- two controls- a mechanical timer, and a full/defrost switch.
> I don't think that thing will ever die!
Just sold mine in a yard sale this weekend and already I'm having
second thoughts. That was one tough oven. I especially like the
use of phase angle control for power control instead of the more
modern duty cycle control. Easier on the magnetron plus doen't
cause the hot spots that duty cycle control does.