Strange microwave oven features

[The Real Andy]

I have a Sharp carousel, the one with the lcd display. I went to open
the door the other day, and kinda pulled it on an angle. To my
surprise the microwave actually switched on. It seems to have 2
interlock switches on the door and when the bottom one is closed, and
the top one is open, the microwave turns on the light and starts to
emit microwaves..

 

[Ken Taylor]

I have a Sharp carousel, the one with the lcd display. I went to open
the door the other day, and kinda pulled it on an angle. To my
surprise the microwave actually switched on. It seems to have 2
interlock switches on the door and when the bottom one is closed, and
the top one is open, the microwave turns on the light and starts to
emit microwaves..

There was a thread on sci.electronics (.design?) a few months back when
someone there claimed a similar thing - no-one was sure if it was a troll or
not. I guess not. Piss-poor design, IMO.

Ken

 

[atec]

if that is the case I expect you will notify the manufacturer ?.

 

[David L. Jones]

I have a Sharp carousel, the one with the lcd display. I went to open
the door the other day, and kinda pulled it on an angle. To my
surprise the microwave actually switched on. It seems to have 2
interlock switches on the door and when the bottom one is closed, and
the top one is open, the microwave turns on the light and starts to
emit microwaves..

I had a Samsung that did exactly the same thing. Switched on when you
pulled slightly on the top of the handle and opened the top interlock
but not the bottom one.
I took it back and got my money back. I did have to demonstrate it on
the shop model to prove that it was a design "feature" and not just a
faulty unit.

Dave

 

[The Real Andy]

I had a Samsung that did exactly the same thing. Switched on when you
pulled slightly on the top of the handle and opened the top interlock
but not the bottom one.
I took it back and got my money back. I did have to demonstrate it on
the shop model to prove that it was a design "feature" and not just a
faulty unit.

Dave

A few lines of the LCD have died. I might inform Sharp they have a dud
in more ways than one.

 

[-=:Install:=-]

Sharp are *well* aware of LCD problems

A few lines of the LCD have died. I might inform Sharp they have a dud
in more ways than one.

 

[Bill Bailley]

I have a Sharp carousel, the one with the lcd display. I went to open
the door the other day, and kinda pulled it on an angle. To my
surprise the microwave actually switched on. It seems to have 2
interlock switches on the door and when the bottom one is closed, and
the top one is open, the microwave turns on the light and starts to
emit microwaves..

A common effect directly related to the light construction and flexibility
of modern microwave oven doors. There are no safety issues here. This will
be well known by Sharp oven service centres and by any salesman with a clue.
(Not a common find these days.)

starts to emit microwaves..<

Not possible, unless the oven door switch wiring/sequence and cook relay
operation has been deliberately modified.


Bill.

 

[The Real Andy]

A common effect directly related to the light construction and flexibility
of modern microwave oven doors. There are no safety issues here. This will
be well known by Sharp oven service centres and by any salesman with a clue.
(Not a common find these days.)


Not possible, unless the oven door switch wiring/sequence and cook relay
operation has been deliberately modified.

Is possible and does happen. The door is still probably sufficently
closed to prevent m/waves escaping. But still poor design if you ask
me.

 

[Bill Bailley]

Is possible and does happen. The door is still probably sufficently
closed to prevent m/waves escaping. But still poor design if you ask
me.

It is important to remember here that simply because the fan and light are
on, it does NOT mean that the magnetron is energized.

I repeat,

"Not possible, unless the oven door switch wiring/sequence and cook relay
operation has been deliberately modified."

Bill.

 

[Franc Zabkar]

I have a Sharp carousel, the one with the lcd display. I went to open
the door the other day, and kinda pulled it on an angle. To my
surprise the microwave actually switched on. It seems to have 2
interlock switches on the door and when the bottom one is closed, and
the top one is open, the microwave turns on the light and starts to
emit microwaves..

Did the fan and carousel motors turn on? Do you have a microwave
leakage detector to verify that the magnetron was operating?


- Franc Zabkar

 

[Malcolm Moore]

It is important to remember here that simply because the fan and light are
on, it does NOT mean that the magnetron is energized.

I repeat,

"Not possible, unless the oven door switch wiring/sequence and cook relay
operation has been deliberately modified."

Bill.

We have an older Sharp Carousel with fluorescent display so the
following may not be relevant to the original observation.

The door is opened by pressing a mechanical button which turns the
light on and releases the door catches. If the mechanical button is
only partially pressed the light comes on, the fan starts and the
turntable rotates, but the magnetron doesn't emit anything (tested by
placing a cup of water in the oven and holding the button in that
position for a minute or so). The door is not released. From memory
there is no switch associated with the release button so presumably
this state is produced by one of the two door interlock switches
operating before the other.
ymmv

 

[Phil Allison]

"Franc Zabkar" <[email protected]

Did the fan and carousel motors turn on? Do you have a microwave
leakage detector to verify that the magnetron was operating?

** One of my RMS Current Monitors would be good for that.





................ Phil

 

[Franc Zabkar]

Is possible and does happen. The door is still probably sufficently
closed to prevent m/waves escaping. But still poor design if you ask
me.

I can't see that it is possible unless the cook relay contacts are
stuck closed, or the relay's drive transistor is shorted, or the uP
has glitched into an undefined state.

Ironically, I believe that the microwave oven's behaviour is erring on
the safe side. The symptoms appear consistent with an overly sensitive
door sensor switch. This would cause the uP to believe the door is
open when it is not. The two AC door interlocks probably remain closed
because their actuating levers have a longer travel (?). Sensing that
the door is open, the uP turns on the main relay which normally only
energises the lamp. However, as both interlocks are closed, both the
fan and carousel motor are also energised. This may suggest to the
user that the magnetron is on, but in reality the magnetron is
controlled by a separate cook relay. This relay will remain in the
de-energised state because the uP knows that the door is open, however
slightly.

This is a schematic diagram of my own Philips LE31 oven which I
believe to be a typical design:
http://members.optusnet.com.au/~fzabkar/LE31.jpg


- Franc Zabkar