Oven won't heat even though each component seems to be functional.
I have an LG LRM1250 that won't heat. I have 115VAC to the primary of the transformer and 3-4VAC across the filament taps. Resistance is less than 0.1 ohm across the magnetron terminals and infinity from each terminal to ground. HV transformer tap to ground is ~90 ohm. Diode is ~50Kohm/infinity. Resistance between each capacitor terminal and the case is infinity. The ohm meter deflects then returns to infinity as I switch the leads back and forth across the capacitor terminals. Energizing the transformer while the magnetron is disconnected results in the capacitor holding a charge. The oven is only two years old and the cooking power never decreased before it just stopped heating. I suspect the magnetron, but it appears to test ok and it appears to be in good physical condition. Anyone have any ideas?
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Re: Oven won't heat even though each component seems to...
Even though the magnetron passed the continuity tests, it can still be bad. In fact, most of them fail in ways that do not show up in continuity tests.
And I am 99% certain yours is bad, especially since you have proven that the filament voltage and high voltage DC is being produced and sent to the magnetron.
I must say that the testing you have done is not recommended for people without plenty of experience, but apparently you did it safely. Please don't press your luck, since the high voltage can be instantly lethal.
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Most Frequent Causes for Microwave not working Thermal Fuse
The thermal fuse cuts off power to the microwave if the microwave overheats. To determine if the thermal fuse has blown, use a multimeter to test it for continuity. If the fuse does not have continuity, replace it. The thermal fuse cannot be reset-if the fuse is blown, it must be replaced. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the thermal fuse The thermal fuse cuts off power to the microwave if the microwave overheats. To determine if the thermal fuse has blown, use a multimeter to test it for continuity. If the fuse does not have continuity, replace it. The thermal fuse cannot be reset-if the fuse is blown, it must be replaced. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the thermal fuse
A word of caution.......if you are familiar with microwave ovens, you know how to discharge the big capacitor in the seconday-circuit, and what can happen if you don`t! BE CAREFULL!
If your microwave oven runs normally, but won`t heat, suspect a primary-circuit fuse. Always replace with a fuse of the same voltage and amp rating. Also, check all electrical connections. Again, be sure to discharge the big capacitor so as to avoid dangerous shock.
Another common problem and simple check is the power diode. Simply check for continuity. If you get continuity in both directions with a volt-ohm meter, replace the power-diode.
If you have the proper meter, check the secondary-circuit capacitor. The capacitor can be a little pricey if it is bad.
If that doesn`t do it, the problem is likely the primary-secondary transformer. Unfortunately, the cost of the replacement part is probably more expensive than buying a new microwave oven.
When you say "Everything works as set" do you mean the microwave appears to function properly, but then doesn't heat?
If the magnetron is new, then the magnetron must not be receiving the required high voltage (2000V or more) from the HV circuit. Make sure you've got 120V to the PRIMARY (don't attempt to measure secondary voltage of the HV transformer without special equipment) of the HV transformer. After that check the HV capacitor and diodes. If these components test OK, then either your HV transformer is bad or your new magnetron is faulty. My experience is that the problem is usually in control circuitry, preventing 120V to the HV transformer, or opens/shorts in the HV components (diodes and capacitors).
The main purpose of a microwave oven is to generate microwaves to heat food in the compartment so if it doesn't do that, then chances are that a component has failed. The fact that everything else seems to work suggests that you at least have ac power getting to the controls. You more than likely have a bad magnetron tube , filament transformer or high voltage capacitor that failed as part of the microwave generating system and it is not something that the untrained person should attempt to fix. Even unplugged, the high voltage capacitor remains charged up sufficiently enough to cause serious injury to someone. I've always been an advocate of the good old saying that if the cost to repair exceeds the cost to replace...then simply replace it. Even if you get an appliance tech to examine it, chances are his fee and the components that he finds defective will more than offset a replacement appliance.. I wish I could have suggested a better alternative for you..
If you have plug-in type watt meter, you can check the power draw of the oven when it is heating and it isn't. The magnetron is the primary power consumer of the unit, and by comparing the difference of power you can tell if it is the magnetron. Most likely your intuition is correct.