My Sharp convection microwave (model R-9H66) trips the circuit breaker
everytime it's turned on. It started doing this after its door was slammed
shut by someone. It's obviously shorting somewhere when turned on, and I
took the outer housing off to look at the wiring to see if there was
anything obvious,but didn't notice anything.

Does anyone have any idea what might be wrong or what to look for? It was a
fairly expensive unit when I bought it 6 years ago, and I'd hate to just
through it away, especially if it turns out to be something relatively easy
to repair.

Thanks for any help. I appreciate it.

Pat

I'm not familiar with your model or unit, but there are safety interlocks on
every microwave to assure the door is properly shut to prevent radiation
leakage. These usually come in two flavors, a normally open microswitch
that gets closed to "make" the connection to power the magnetron, and a
second normally closed microswitch that is normally shorted across the
magnetron and opens when the door is shut.

These two switches work in combination and if all works properly, the short
is removed and the power is then applied. In your case, I'd look at the
switch and the alignment to make sure the one that opens is in fact opening
properly. Sounds to me like it may have been jarred and is no longer aligned
properly so stays closed creating the short and blowing your breaker (most
units I've seen have a 15A slow blow fuse that goes first before the
receptacle breaker).

Good luck and hope this is helpful.

Bob

"Pat" wrote in message
news:a9omd.617800$8_6.3758@attbi_s04...
My Sharp convection microwave (model R-9H66) trips the circuit breaker
everytime it's turned on. It started doing this after its door was
slammed
shut by someone. It's obviously shorting somewhere when turned on, and
I
took the outer housing off to look at the wiring to see if there was
anything obvious,but didn't notice anything.

Does anyone have any idea what might be wrong or what to look for? It was
a
fairly expensive unit when I bought it 6 years ago, and I'd hate to just
through it away, especially if it turns out to be something relatively
easy
to repair.

Thanks for any help. I appreciate it.

Pat

Check for defective safety switches, and replace as necessary. It is rare,
but there may be a short in the power supply, or the HV section.

Take care that these are extremely dangerous to service yourself, unless you
really know what you are doing. As for replacing the safety switches, use
the origional manufacture parts only, and make sure you know how to adjust
their placement. Check for the proper tollerance of how the door seats, and
that the play in the hinges is correct.

After replacing any components, especialy around the door area, it is
strongly recomended to take measurments for any possible radiation leakage,
in case the door may not be seating properly. If the door has been slammed
so hard to damage the switches, a radiation leakage test would be in good
order.

I would recomend that you take the unit to an authorized service center
where they service microwave ovens, for proper and safe service, unless you
are properly trained, equiped, and are experienced in this type of service
work. The microwave oven is the number one dangerous appliance in the home.
The next ones down are the TV set, and the computer monitor.

As for microwave radiation, at low levels this is not able to be felt, but
damage may be done to anyone within its range. There are numerous safety
articles about this. http://www.fda.gov/cdrh/consumer/microwave.html

--

Jerry G.
======


"Pat" wrote in message
news:a9omd.617800$8_6.3758@attbi_s04...
My Sharp convection microwave (model R-9H66) trips the circuit breaker
everytime it's turned on. It started doing this after its door was
slammed
shut by someone. It's obviously shorting somewhere when turned on, and
I
took the outer housing off to look at the wiring to see if there was
anything obvious,but didn't notice anything.

Does anyone have any idea what might be wrong or what to look for? It was
a
fairly expensive unit when I bought it 6 years ago, and I'd hate to just
through it away, especially if it turns out to be something relatively
easy
to repair.

Thanks for any help. I appreciate it.

Pat

FYI: I Never work on Microwave ovens. They simply are not worth the
trouble or RISK to me. Realize that the capacitor in a microwave oven
stores a charge roughly equivalent to the LifePak defibrillators we are
seeing advertised on tv. If you get across it the wrong way with it
charged at the wrong time in your heartbeat, boom, your probably dead
unless medical help arrives in a few minutes, at a minimum you just did
damage to your heart. That would be during the T wave of your EKG.

At the very least, everyone I know who works on microwave ovens now, has
insulative gloves up to the elbows on at least one arm AND double checks
the high voltage stored on the capacitor with a high voltage probe.

My suggestion, pay someone the $50 labor to work on it for you. If someone
really does not know exactly what they are doing and is willing to accept
the risk, $50 or so, is simply not worth the risk for the average Joe
owner.

David

Read the RepairFaqs regarding these infernal machines before even attempting
service. There are many posts to Sam's Site within this and other
newsgroups. As stated, these can be EXTREMELY DANGEROUS to service for the
un-informed. Occasionally LETHAL!! BTW, I agree that it is highly probable
a defective or miss-aligned switch, exp since some how "the door had been
slammed"!!
"dkuhajda" wrote in message
...
FYI: I Never work on Microwave ovens. They simply are not worth the
trouble or RISK to me. Realize that the capacitor in a microwave oven
stores a charge roughly equivalent to the LifePak defibrillators we are
seeing advertised on tv. If you get across it the wrong way with it
charged at the wrong time in your heartbeat, boom, your probably dead
unless medical help arrives in a few minutes, at a minimum you just did
damage to your heart. That would be during the T wave of your EKG.

At the very least, everyone I know who works on microwave ovens now, has
insulative gloves up to the elbows on at least one arm AND double checks
the high voltage stored on the capacitor with a high voltage probe.

My suggestion, pay someone the $50 labor to work on it for you. If
someone
really does not know exactly what they are doing and is willing to accept
the risk, $50 or so, is simply not worth the risk for the average Joe
owner.

David

"Art" writes:

Read the RepairFaqs regarding these infernal machines before even attempting
service. There are many posts to Sam's Site within this and other
newsgroups. As stated, these can be EXTREMELY DANGEROUS to service for the
un-informed. Occasionally LETHAL!! BTW, I agree that it is highly probable
a defective or miss-aligned switch, exp since some how "the door had been
slammed"!!

And if the oven is unplugged, working around the area of the door switches
is safe. However, you do have to know where that is and where NOT to go!

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header is ignored.
To contact me, please use the Feedback Form in the FAQs.

Now that you scared the guy to death .....


its probably a door switch that jammed when someone slammed it . look in
where those plastic spades on the door poke into the front there are
some squarish black switches that get pushed when the spades go through
the holes .
Each switch has a little ( probably ) red nub that clicks when you push
it in . You can reach in and push those with something to see if they
mechanically click .
If you do find the bad one you can unplug the wire from the back of it
and note where they went and take the switch to some repair senter for a
new one . Put it back the same way it came out . You dont need to do any
of those silly tests .... those are for ovens that ha door damage .
Just dont touch the wires coming out of a big capacitor ( silver oval
like can mounted to the bottom or rear of the case )

Thanks to everyone for all the replies and warnings. I've worked around
electronics before and know stay away from the caps or make sure they're
discharged and everything is unplugged if I must go near them.

If it turns out to be a bad switch (as seems likely) where's a good place to
get a replacement?

Thanks again. -Pat



"Ken G." wrote in message
...
Now that you scared the guy to death .....


its probably a door switch that jammed when someone slammed it . look in
where those plastic spades on the door poke into the front there are
some squarish black switches that get pushed when the spades go through
the holes .
Each switch has a little ( probably ) red nub that clicks when you push
it in . You can reach in and push those with something to see if they
mechanically click .
If you do find the bad one you can unplug the wire from the back of it
and note where they went and take the switch to some repair senter for a
new one . Put it back the same way it came out . You dont need to do any
of those silly tests .... those are for ovens that ha door damage .
Just dont touch the wires coming out of a big capacitor ( silver oval
like can mounted to the bottom or rear of the case )

Pat,

I generally look in the owner's manual and contact the manufacturer (using
the phone number listed or a visit to their web site) or the closest
authorized service center. Usually you can order parts, especially the
commonly replaced items like the microswitches, diode, HV capacitor, etc.

Another option I've used is at the following repair web site:

http://www.repairclinic.com/0047_6.asp

They handle parts and provide a lot of basic troubleshooting info, assembly
drawings, etc. for many common appliances in use today. In either case, be
prepared to pay more than what you might expect since you are paying for the
convenience of having the distributor stock these items and not just the
manufacturing cost.

Good luck and exercise caution when working on the microwave.

Bob

"Pat" wrote in message
news:zSImd.108022$R05.11573@attbi_s53...
Thanks to everyone for all the replies and warnings. I've worked around
electronics before and know stay away from the caps or make sure they're
discharged and everything is unplugged if I must go near them.

If it turns out to be a bad switch (as seems likely) where's a good place
to
get a replacement?

Thanks again. -Pat

It's fixed!

Turns out one of the switches had been pushed slightly out of the plastic
bracket that was holds it in place, although it wasn't real obvious until I
looked closely. When I pushed on the back of it, it snapped back into place
and everything started working again as normal. It must have been knocked
out of place when the door was slammed.

A very easy fix after all, but I would have never found it if someone hadn't
suggested checking it.

Thanks again to everyone. You've save me several hundred dollars. Does
make me wonder how many microwaves end up by the curbside because of simple
things like that.

Thanks again,

Pat




"Bob Shuman" wrote in message
...
Pat,

I generally look in the owner's manual and contact the manufacturer (using
the phone number listed or a visit to their web site) or the closest
authorized service center. Usually you can order parts, especially the
commonly replaced items like the microswitches, diode, HV capacitor, etc.

Another option I've used is at the following repair web site:

http://www.repairclinic.com/0047_6.asp

They handle parts and provide a lot of basic troubleshooting info,
assembly
drawings, etc. for many common appliances in use today. In either case, be
prepared to pay more than what you might expect since you are paying for
the
convenience of having the distributor stock these items and not just the
manufacturing cost.

Good luck and exercise caution when working on the microwave.

Bob

"Pat" wrote in message
news:zSImd.108022$R05.11573@attbi_s53...
Thanks to everyone for all the replies and warnings. I've worked around
electronics before and know stay away from the caps or make sure they're
discharged and everything is unplugged if I must go near them.

If it turns out to be a bad switch (as seems likely) where's a good
place
to
get a replacement?

Thanks again. -Pat

"Pat" wrote in message
news:kPJmd.43292$V41.38458@attbi_s52...
| It's fixed!
....
| Thanks again to everyone. You've save me several hundred dollars. Does
| make me wonder how many microwaves end up by the curbside because of
simple
| things like that.

It's said that microwaves don't burn out, they rust out. My 20 year old one
still works after daily use, long after I thought it would die.

N

This is probably a problem with your microwave oven door interlock switches.

Here's a quote from repairfaq website:
http://repairfaq.ece.drexel.edu/sam/....htm#mictstris

"Even slamming the door really hard has been known to knock an interlock
switch out of position, resulting in breaker tripping at the electrical
service panel whenever the microwave oven door was closed. (Another reason
to stay calm after accidentally nuking that bagel for 5 minutes on HIGH!) So
if there was some kind of "event" after which the microwave failed, check
the interlock mechanism first - a switch may just need to be popped back
into place."

Interlock switches
Various door interlock switches prevent inadvertent generation of microwaves
unless the door is closed completely. At least one of these will be directly
in series with the transformer primary so that a short in the relay or triac
cannot accidentally turn on the microwaves with the door open. The
interlocks must be activated in the correct sequence when the door is closed
or opened.

Interestingly, another interlock is set up to directly short the power line
if it is activated in an incorrect sequence. The interlocks are designed so
that if the door is correctly aligned, they will sequence correctly.
Otherwise, a short will be put across the power line causing the fuse to
blow forcing the oven to be serviced. This makes it more difficult for an
ignorant consumer to just bypass the door interlocks should they fail or to
run the oven with an open door as a room heater - and protects the
manufacturer from lawsuits. (That interlock may be known as a "dummy switch"
for obvious reasons and is often not even mentioned in the schematic/parts
manifest.) Of course, should that switch ever actually be used, not only
will the fuse blow, but the switch contacts will likely be damaged by the
high initial current! This also means it probably wouldn't be a bad idea to
replace the interlock switch which might have been affected if your oven
fails with a blown fuse due to a door problem.

Failed door interlocks account for the majority of microwave oven problems -
perhaps as high as 75 percent. This is not surprising considering that two
of the three switches carry the full oven current - any deterioration of the
contacts results in increased resistance leading to their heating and
further deterioration. And, opening the door to interrupt a cook cycle
results in arcing at the contacts. Complete meltdowns are not unusual! If
any defective door switches are found, it is probably a good idea to replace
all of them as long as the oven is already apart.

The typical door switches and their function:

* Door Sensing: Input to the microcontroller to indicate the state of
the door.

* Interlock Monitor: Shorts out the AC line (and blows the main fuse)
should the Primary Interlock not open due to incorrect sequencing of the
door switches or a failed switch.

* Primary Interlock: In series with the high voltage (magnetron) power
supply so cuts power when the door is open.

Note that if the Door Sensing switch should malfunction, peculiar behavior
may occur (like the fan or turntable operating at the wrong time) but should
never result in microwaves being generated with the door open.


Testing and replacing of interlock switches
With the oven unplugged, put an ohmmeter across the AC input just before the
interlocks (but beyond the power relay or triac if it precedes these). Open
and close the door slowly several times - there should be no significant
change in resistance and it should be more than a few ohms. If it approaches
zero while opening or closing the door, the interlock switches and door
alignment should be checked. (You may need to disconnect one side of the
transformer primary since its resistance is a fraction of an ohm. Refer to
the schematic pasted inside the cover.)

Replace with switches having a precisely identical fit and equal or better
electrical specifications (terminal configuration, current rating). When
removing the old switch make a note as to where each wire goes. Check the
embossed marking on the old switch - don't depend on location as your
replacement might just have a different arrangement. Make sure the new
switch aligns correctly with the actuating mechanism and then check for
correct electrical operation with an ohmmeter before applying power.

Even slamming the door really hard has been known to knock an interlock
switch out of position, resulting in breaker tripping at the electrical
service panel whenever the microwave oven door was closed. (Another reason
to stay calm after accidentally nuking that bagel for 5 minutes on HIGH!) So
if there was some kind of "event" after which the microwave failed, check
the interlock mechanism first - a switch may just need to be popped back
into place.


Credit to author :

Notes on the Troubleshooting and Repair of Microwave Ovens
Version 3.44
Copyright © 1994-2004
Samuel M. Goldwasser
--- All Rights Reserved ---
http://repairfaq.ece.drexel.edu/sam/....htm#mictstris


From Jim

Remove 99 to reply.



----- Original Message -----
From: Pat
Newsgroups: sci.electronics.repair
Sent: Tuesday, November 16, 2004 9:29 AM
Subject: Sharp microwave oven problem


My Sharp convection microwave (model R-9H66) trips the circuit breaker
everytime it's turned on. It started doing this after its door was slammed
shut by someone. It's obviously shorting somewhere when turned on, and I
took the outer housing off to look at the wiring to see if there was
anything obvious,but didn't notice anything.

Does anyone have any idea what might be wrong or what to look for? It was a
fairly expensive unit when I bought it 6 years ago, and I'd hate to just
through it away, especially if it turns out to be something relatively easy
to repair.

Thanks for any help. I appreciate it.

Pat

Failed door interlocks account for the majority of microwave oven
problems -
perhaps as high as 75 percent.

I was interested in the assertion that door interlock micro-switches are the
most common failure in microwaves.

I have just looked at our repair database and I have repaired about 280
microwaves over the past 18 months makes include Sharp - Panasonic -
Samsung - LG - old Toshibas & Sanyo.

I would say the most common faults are
1) Sharp CPUs
2) HV diodes
3) Magnetrons
4) HV capacitors
With microswitch trouble maybe joint fourth or maybe lower.

The situation of the Sharp CPU perhaps needs a little explanation.
Most of the ovens we repair are Sharp, with model numbers beginning with R-
The CPU is integrated to an LCD display, they are connected to each other
with a ribbon cable bonded to the glass and the PCB. After a while some /
most LCD segments fail to display. I suspect the problem is with the bonded
cable, but as there is no reliable means of repair (that I know) they all
get replaced.

It just occurred to me that here in the UK we use real electricity ie
230-240V, therefore the current is only half of a N American oven of the
same power. Typically the microwave side of a domestic oven here will be
protected by an 8 Amp fuse. Does this explain the anomaly?



Graham.


%Profound_observation%