Hamilton Beach 33103BC toaster oven - lower elements don't work, upper ones do

[Hogwild]

Hi everyone:

Extreme newbie here, but like to take things apart. Hamilton Beach 31103DC toaster oven. Lower elements heat fine. Upper elements don't heat at all.
I can't find any obvious signs of continuity problems anywhere. One multi-position switch controls both upper and lower elements.

Switch is labelled Hua Li Lei FZ31-10. I'm not smart enough to understand the repercussion of the pinouts.

One terminal on the switch seems to move up and down (but not left and right). On the same side, the switch casing seems to be not properly fastened to the rest of the switch. I can't find any thermistor or anything, but I guess it could be hidden.

Should I assume elements or switch are broken, or am I even going in the right direction here? Remember, I'm a newbie.

Thanks

[bob91343]

That symptom is usually caused by burned out elements.  Disconnect them and measure their resistance.  It is also possible that a switch is bad but then it wouldn't work at all.

[Hogwild]

I think the wires to the elements are actually welded on (not just soldered). Is there any way to tell for sure?

Yes, that's what I was thinking about the switch. I don't know much, but this thing has a multi-position switch for which one position turns on the lower elements, the other position turns on the upper elements. Isn't it possible that the switch's contacts or inner mechanism are shot but for only one position and not others?

[Hogwild]

If I do disconnect the elements, what resistance should they be?

I can't find another switch to replace the bad one at a really reasonable price. $20.00 plus shipping. Hmmm...

[WattsThat]

Actual resistance really doesn't matter as you’re looking for an open circuit but... if it is a purely electro-mechanical device with no electronics in it, you should be able to measure the resistance of the good elements right at the plug with the timer turned on. Divide that by 2 for the resistance of one element.

Or, the easy way if there is a wattage listed on the device, solve for R and divide by 4. R = E^2 / P

[Hogwild]

Sorry, being a newbie, I"m not sure what you mean. You mean one DMM probe on one AC plug terminal and the other probe on the other terminal? Or did you mean something else? Yes, I believe it's all electromechanical, I can't see any semiconductors.

BTW, I don't know if it's relevant, but when I put the DMM probes on the element ends themselves, I measure somewhere in the 9.6 ohm region. OF course, since they're connected to other things, I don't know if those other things are affecting the measurement.

[bob91343]

That doesn't tell much.  The elements are probably in parallel so you won't find an open one that way.  When you change switch settings do the readings change?  Across the power plug, that is.  Is this wired for 120 or 240?

[Hogwild]

With DMM leads across the power plug, here's what I get with timer on:

- Rotisserie (position 1) on switch: 2.674K

- Bake (position 2) [bottom elements] on switch: 29.5-31M

- Convection (position 3) : 0.465M

- Broil (position 4) [ top elements] : OL

Does the very high resistance on Bake suggest something?

[WattsThat]

Assuming it’s 120v, 9.6 ohms sounds about right for an counter-top oven. That would approximately 12 amps and 1400 watts. That’s about the limit for a US standard outlet which is 15 amps max. Some are 20.  I assume it’s the same up north.

None of the ohm measurements at the plug make any sense.

[Hogwild]

O-kay. Then, what do you suggest I do next?

[bob91343]

All your measurements are high, in the megohms.  I would expect them to be under 100 Ohms.

[Hogwild]

Yeah, that's what I was thinking. Maybe my meter is dying?

[tunk]

Short your multimeter test leads, you should get a reading
close to zero (less than 1 ohm). If not, check each test
lead by disconnecting one of them, and then putting the tip
of the other into the socket of the test lead you just took
out. If one of them shows a high resistance, it's bad.
If both is high, then both leads are bad, or your meter
is bad.

If your meter is ok, then it could be the owen switch.

[Hogwild]

Thanks. I already did that, but I'll do it again. It is showing 0 resistance. I've used the DMM on other things recently, and it has been accurate.
So, likely the switch?

[drussell]

Thanks. I already did that, but I'll do it again. It is showing 0 resistance. I've used the DMM on other things recently, and it has been accurate.
So, likely the switch?

No, we don't know that yet...

The readings you are getting on your DMM make no sense for the observed behavior of the bake element working but broil element not working.

It might be the switch not turning on the broil element (top) in the toast and broil modes, but you should still be seeing the bake element (lower) in circuit in non-broil modes with your meter, since it does heat up.

Something is wrong with your measurements.  Until your measurements agree with the observed behavior in operation, do not hastily jump to conclusions about where the actual fault lies!

More sleuthing is required!   

Edit:  Some good, clear photos of the guts of the unit would be helpful for us guide you.

[Hogwild]

When I meausred the elements directly, the bottom ones and top ones were both somewhere near the 10R area. The bottom ones measured slightly differently than the top ones.

I'll get some pics and post back with them. My camera battery just died, so I'll do that later today or tomorrow. Thanks for all this. If I can fix this, I'll make my 95-year-old Mom very happy.

[Hogwild]

Do these help at all?


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[tunk]

Looks like there's no electronics.
Use your multimeter to check for continuity everywhere:
elements, cables, connectors, switch(es) etc. NB: Spade
connectors can go bad. The timer should be ok - if it's
bad, I guess nothing would work.

[drussell]

The contacts on the A terminal on the switch (blue wire) are burned.

You might be able to disassemble the switch and clean up the contacts if they're not beyond repair, otherwise you'll need a new switch.

Edit:

[Hogwild]

That's what I thought. Glad my instincts were good. Does one just pry open the side of the switch that's already not flush? As I said earlier, that same terminal is also moving up and down in the switch. What does one use to clean the switch? Contact cleaner?

[drussell]

You will need to file it down, or sandpaper or something, it will be quite charred.

First remove the switch from the toaster oven and see if you can figure out how it snaps together and post a picture of how bad that contact is.  It was obviously making poor connection and got super hot, melting the case of the switch. 

Depending on how long it was like that there may not be much left of the contact to try to repair. 

[Hogwild]

After what you described, I think it might be better/safer to just buy a new switch. I see them in a few places but $USD 24.00-28.00 !

That's crazy. I bet they sell them in China for 60 cents.

[drussell]

Does one just pry open the side of the switch that's already not flush?

It looks like there are little clips on the end caps that pop into holes in the main switch body, if you press on those with a small screwdriver or something you should be able to pop them free and open the switch.

[drussell]

After what you described, I think it might be better/safer to just buy a new switch. I see them in a few places but $USD 24.00-28.00 !

Well a new switch is certainly the best way to go but since it is toast anyway (har har) there's nothing to lose by at least trying to open it and see just how charred it is, how badly it failed.

[tunk]

To open it: I guess there's four tabs, one to the
right of "A", one above "16A" and two on the other
side. And you may have to replace the spade connector,
it may have been weakened, loosing it's tension.
It could possibly also have been the cause of the
problem.