Funny thing is, nothing seems any different than before. No extra noise either.

Have you looked in the fridge lately?

 

Have you looked in the fridge lately?

Since this happened i havent opened the refrigerator, too scared of what might be living in there

That movie was great.

 

I have a question about the microwave. Have you marked the rotating plate to see if the cook plate goes to the same place every time? Or is the cook plate going to a random spot each time?

 

I have a question about the microwave. Have you marked the rotating plate to see if the cook plate goes to the same place every time? Or is the cook plate going to a random spot each time?

That's actually a very good question.

the movement is random relative to the glass plate underneath, but strongly correlated to the oven cavity.
First, the movement of the plate is a little strange in that the rotation changes direction now and then when the oven is turned on. One time it will turn clockwise, then other times counter clockwise, as if looking straight down from the top through the top of the oven standing in front of it.
So the close lip of the glass plate sometimes goes to the right, then other times to the left, and that itself seems to be random.
What i noticed most is when the lip moves to the right which i would call clockwise.

When it moves in that direction, the cook plate on top of the glass plate moves toward the back of the oven id' say within a 1/4 turn of the glass plate, and that is fairly quick within about 3 seconds.
It may seem interesting that the oven is tilted back slightly. That means the front of the oven is slightly higher than the back. That is because i made up special feet pads that raise the front up slightly to make up for the natural tilt of the shelf it is located on. The shelf front lip is slightly lower than the back so to make up for that i made up feet pads for the two feet in the front to raise them slightly.

Now that would explain the movement, or at least could, but the thing is it has been this way ever since maybe the 5th day since i bought the oven which was at least 5 years ago i think and the strange movement never happened before this. Add to that the silicone feet create more drag for the cook plate so it takes more force to slide it, yet it still slides in the same way.

I should have taken a video of this but i have the wood square glued to the center of the glass plate now so i'd have to rip it off to get a video of the action.

LATER:
I just checked my records, i had the over for over 9 years. Wow time goes fast. But you see why this is so puzzling. Why would it start doing this now.
I've used that oven at least once per day for all that time.

I almost forgot to mention that i also heat up water in a cup placing the cup in the center. The cup does not move. I've used styrofoam cups and a borosilicate glass cup with flat bottom and they dont move. Maybe the weight has a lot to do with it the cups always have at least 8 ounces of water in them. However, chicken legs on the plate are not that light weight.

I thought of putting small silicone 'dots' around the bottom so it would hold the cook plate in place, but i dont want it to be too hard to clean the glass plate which must be cleaned now and then. The dots would get in the way of a nice clean sweep of a slightly abrasive sponge.

LATER LATER:
I have one 'theory'. That is, when the glass plate starts to move it jerks suddenly when it starts to turn and maybe that allows the cook plate to overcome the sticking friction and so it becomes easier to keep it moving after that. Still it seems like a lot.
Maybe the motor is sticking for some reason so it starts to turn abruptly instead of with a smooth gradual speed increase.

Sticking friction can be quite substantial but once overcome the regular translational or rotational friction could be much less. To test for this i would have to find a way to stop the cook plate from moving until AFTER the glass plate started to rotate and then release it. That would mean the sticking friction would still be a large factor in governing the movement.
I'll have to check for a buildup of something around the motor shaft to see if anything binds it temporarily.
I had a motor go bad in another oven i had long ago but i know why that happened is was because salt water got into the motor and damaged some of the winding turns. But that motor failed completely and had to have some windings removed (not many so it still worked).
This might be different though it might just be sticking so the motor builds up torque before it begins to move, then lets go all of a sudden and that jerks the plate.
This is all still just a 'theory' though need to be looked into more carefully.
Still open to ideas and suggestions.

 

Do you have an accelerometer? The output displayed on your scope could probably tell you what is happening in different horizontal directions.
.

 

Maybe the motor is sticking for some reason so it starts to turn abruptly instead of with a smooth gradual speed increase.

That was why I asked my question. Stiction can cause things to move erratically and put the cook plate in different positions.

 

Do you have an accelerometer? The output displayed on your scope could probably tell you what is happening in different horizontal directions.
.

Not one i can put in the microwave unless i could disable the tube. Not sure i want to try that
Interesting idea though.
Maybe i can put something near the edge of the glass plate and take a video as i turn the oven on. Then analyze the movement of the object.

 

That was why I asked my question. Stiction can cause things to move erratically and put the cook plate in different positions.

Yeah i have to check it for something that maybe got into the motor. I think i see it jerk.

 

Always the same plate? Have you tried a plain generic paper plate?

Ron

 

I heard you can see ghosts if you look through Polarized films with your back to the full moon at midnight. I'd try that has you heat up some Hot Pockets on that plate.
If you don't see the ghosts and your plate doesn't move from the center, either the ghosts were afraid to move your plate or the same vibrations were not present when you reoriented your microwave to allow the moon to be at your back.

 

Not one i can put in the microwave unless i could disable the tube. Not sure i want to try that
Interesting idea though.
Maybe i can put something near the edge of the glass plate and take a video as i turn the oven on. Then analyze the movement of the object.

You don't need to put the accelerometer inside the oven. If you have one with a magnet attached, just stick it on the front or side of the case. Vibrations will be transmitted through the frame and casing. If you don't have one with a magnet, a thin layer of bee's wax will hold it in place and conduct the vibrations. If you try it in different locations, you can probably determine the direction of the maximum vibrations.
If you don't have memory on your scope, you can input the vibrations to a computer sound card and save it as a .wav file. That will allow you to use spectrum analysis later to give you more information.

 

You don't need to put the accelerometer inside the oven. If you have one with a magnet attached, just stick it on the front or side of the case. Vibrations will be transmitted through the frame and casing. If you don't have one with a magnet, a thin layer of bee's wax will hold it in place and conduct the vibrations. If you try it in different locations, you can probably determine the direction of the maximum vibrations.
If you don't have memory on your scope, you can input the vibrations to a computer sound card and save it as a .wav file. That will allow you to use spectrum analysis later to give you more information.

interesting idea i'll have to think about it but i'd have to get what you are talking about.

I did take the video, and it appears that the glass plate is not jerking. If it does jerk it's hard to notice.

You don't need to put the accelerometer inside the oven. If you have one with a magnet attached, just stick it on the front or side of the case. Vibrations will be transmitted through the frame and casing. If you don't have one with a magnet, a thin layer of bee's wax will hold it in place and conduct the vibrations. If you try it in different locations, you can probably determine the direction of the maximum vibrations.
If you don't have memory on your scope, you can input the vibrations to a computer sound card and save it as a .wav file. That will allow you to use spectrum analysis later to give you more information.

Always the same plate? Have you tried a plain generic paper plate?

Ron

Oh yes that is interesting maybe a paper plate under the plate i normally use. Thing is now i'd have to tare off the wood square in the center it's glued on Would be interesting though maybe it would provide more friction.

 

I heard you can see ghosts if you look through Polarized films with your back to the full moon at midnight. I'd try that has you heat up some Hot Pockets on that plate.
If you don't see the ghosts and your plate doesn't move from the center, either the ghosts were afraid to move your plate or the same vibrations were not present when you reoriented your microwave to allow the moon to be at your back.

Well i would but the problem has gotten much worse.
Now the ghosts are eating the food before i can take it out of the oven so i'm starving over here.
Another time it looked like an alien flew the plate right out the front door like a flying saucer soon as i opened it and it took off out the window looked like it was heading toward the Andromeda galaxy. Proof of aliens after all.
Har har

 

You are not trying to make absolute measurements, so if you don't have an accelerometer, you can use just about any type of microphone held in contact, with the diaphragm open to the air and parallel to the microwave case. An electret should work well because of its low mass.

 

If you do get a recording of the vibrations, spectrum analysis will show you the vibration amplitude and frequencies of the rotation of the motor and gears, and the meshing of the different gear teeth. I wrote some complex spectrum analysis software for a customer a few years ago to detect wear in bearings and gear teeth in motor driven gear boxes. It is very effective as a diagnostic tool.

 

This is getting a bit silly. It's obviously vibrations causing it and you don't need accelerometers or anything else to measure it. Put a cup of water in it. Do you see ripples? Vibration.

 

If you do get a recording of the vibrations, spectrum analysis will show you the vibration amplitude and frequencies of the rotation of the motor and gears, and the meshing of the different gear teeth. I wrote some complex spectrum analysis software for a customer a few years ago to detect wear in bearings and gear teeth in motor driven gear boxes. It is very effective as a diagnostic tool.

Hi,

That's interesting thanks. I did some math on gear meshing years ago turned out to be very very complicated. Gear slop and everything, tooth shape, etc. Then to calculate the exact movement from those specs. It's interesting though.

 

This is getting a bit silly. It's obviously vibrations causing it and you don't need accelerometers or anything else to measure it. Put a cup of water in it. Do you see ripples? Vibration.

Hi,

Yes i can try that, but i seem to have the problem solved maybe i'll just go with that for now. The square piece of wood in the center keeps the cook plate nearly centered, and if i modify the edges of the wood i can probably get it to stay perfectly centered.

While i am at it maybe i will experiment with the oven mounting angles, tilting one way or another.
I can try to tilt it in a way that maybe counteracts the movement or nearly so.
Might be hard to tell now though because with the wood in there it doesnt move that much, although it does move a little maybe 1/4 inch to one side.