Whirlpool Combi Microwave oven

Surprising, but a HIGH reistance would not blow the fuse. What I'm guessing is there is a short in the SECONDARY, and it draws too much current when energized due to that. Thus, the delayed blow of the fuse.

You should also check the primary to the transformer frame. Must be infinite resistance. Anything less indicates short to frame.

Jon

Many microwave issues including the one you describe can also be the magnetron.

I'd go through those tests first. If it lost heating capacity gradually or sometimes would shut off too early, I would definitely suspect the magnetron.

The interlock switches I believe basically work where two allow power to pass and the other is across the line in an open position, so the fuse blows immediately.

Also 0.2 to 0.5 ohms is VERY difficult to measure without a 4 or 5 wire ohmeter or a 4 terminal measurement. Your test leads and internal meter connections can EASILY have 1 ohm of resistance each.

A way to measure low resistance values is to measure the current through the device and the voltage across it. You can add series resistance and measure the voltage across the known resistor and convert that to a current.

If I'm right, your meter is not capable of measuring 0.2 to 0.5 ohms.

I have not noticed a gradual loss in heating capacity. The problem with the microwave function happened suddenly after the microwave oven came out of storage after about 2 months and carried back into the kitchen.

And the fuse doesn't blow immediately, after all my searching etc. the microwave function worked for 2 - 3 seconds.

hmeter or a 4 terminal measurement. Your test leads and internal meter con nections can EASILY have 1 ohm of resistance each.

the device and the voltage across it. You can add series resistance and me asure the voltage across the known resistor and convert that to a current.

Thanks Ron, but would the meter be correct enough to see a difference betwe en 0.5 or 2.5? Or are both my measurements likely unreliable? If I adjust t he ohm meter to 0 ohm while shorting the test pins, then a subsequent readi ng of 2.5 ohm should be in addition to the internal resistance of the leads etc, and therefore reasonably accurate? It's a pretty robust analogue mete r.

ent

Thanks Jon, there was this typical smell of electric components overheating after the 2 - 3 second running of the microwave function, and I imagined I felt the transformer to be slightly warm to the touch afterwards. But then why would the next fuse also blow with the primary of the transformer (bot h terminal) disconnected and taped up?

Den 10-03-2015, skrev Ron D.:

Btw, it is relativily easy to measure the actual heating capacity of a microwave oven.

Measure the time to heat a glass of water to boiling point.

Temperature rise 100C-15C = 85K Energy used = 1076.2 J/K * 85K = 91477 J Time: 2min 24 sec = 144 sec Power = 91477 J / 144 sec = 802.4 J/s = 802.4 Watt

This is in SI-units.

If your measurements are based on the phalanges of ancient english royalty, your constants may differ.

Thanks,

I might do that when it works again....

I'd be wary of the cap or diode. Can you power it up again with just the magnetron disconnnected to see what happens? If it doesn't blow a fuse your magnetron is what is bad.

Repair of Microwave Ovens I tested:

switches, three use only the two terminals to make a contact. The fourth u ses all three terminals, to break and make contact. Switch 4 was a bit dodg y so I swapped it with Switch 1:

tch 4)

tch 1)

.2 typical)

cause the fuse to blow when I start the cook cycle? I would expect the opp osite to be true, however:

ary winding disconnected I switched it on. The conventional oven worked, an d heated. When I pressed the microwave button the fan worked and the fuse d idn't blow . So I assumed the transformer was faulty. I then reconnected th e transformer and tested the microwave function. It worked for three second s and then blew the fuse, 'confirming'(?) that the transformer was faulty. I replaced the fuse, disconnected the transformer again and tested again. T he conventional oven worked again, and when I pressed the microwave button the fan worked, but the fuse didn't blow. 'Confirming'(?) again that the tr ansformer was faulty. Then I put the microwave oven back in the kitchen cab inet and demonstrated that it worked, partially, but the fuse blew...... su ggesting again that the switches are (may be) faulty.

magnetron disconnnected to

The fuse blew with the transformer disconnected, but not immediately. If it blew immediately I would have thought the door switches were at fault, but now I'm not sure.