Amana RR-10 Microwave repair

[Larry B]

I know, this is ancient but i love it because it is an old Buick in disguise (lots of chrome).

The display/control module has gone completely dead but it is not the module itself. However, the Light switch does operate the light in the cooking cavity so the module is getting 120VAC. I have an old rusty RR-10 in the garage for testing purposes and the module works in that one. So..... what would cause the module to do this? Is there a safety device in the oven itself that could go bad and cause this condition?

Thanks, Larry

[Tony Hwang]

Hmmm, Module is not getting the juice(no power).

[Larry B]

Where would I find the tube thermal switch and are they stardard for microwave ovens? Does it look like a Klixon on an air-con compressor?

Thx

[hrhofmann]

I would start by checking the line fuse. There should be a schematic somewhere on the inside of the removable cover, that's the place to start tracing power.

[jamesgangnc]

There are often multiple thermo switches as well as redundant door switches. On many of them one of the door switches intentionally blows the internal fuse. There may be a transformer in one that old to supply low voltage to the control unit. Otherwise start tracing power. Be really careful as a thousand watts of high voltage, >2000, will kill you deader than a doorknob.

[Larry B]

There are often multiple thermo switches as well as redundant door switches. On many of them one of the door switches intentionally blows the internal fuse. There may be a transformer in one that old to supply low voltage to the control unit. Otherwise start tracing power. Be really careful as a thousand watts of high voltage, >2000, will kill you deader than a doorknob.

The scematic shows the tube thermal switch in line with the power to the module. The module has its own low volage power supply. I'll jumper the thermal switch tonight first to see if I get a display, then, if not, go on to the internal fuse. I'll be back!

Am I correct that if the unit is unplugged, the danger is from the capacitors?

[jamesgangnc]

The high voltage circuit in just about all of them includes a voltage doubling circuit off the high side of the high voltage transformer. There will be a pretty good sized high voltage capacitor in that circuit. Fairly easy to spot. Some will have a built in x megohm bleed down resistor in them but assume not. The chassis is often one leg of the high voltage circuit so it's easy to get shocked. The paperwork inside should tell you to short out the cap before working on it. Truth is that the capacitor, while it will shock the crap out of you, is not likely to kill you. It's accidentally contacting the high voltage side while taking readings that is the main danger. You should be able to check a lot of the safety devices with an ohm meter. The schematic will show you where you could check for open or closed.

[jamesgangnc]

DO NOT THINK that regular probes are safe. The high voltage side will jump through regular insulation on a vom lead/probe. Make damn sure you know what you are checking if you use a meter on it with it powered up. If you are the least bit uncertain, clip the leads on with it powered down and then power it up. That way the worst that happens is you fry your vom.