How to check high voltage in a microwave. Microwave Oven High Voltage Transformer Troubleshooting

In order for this instruction to be useful to all customers, we will consider testing the functionality using the example of an expensive, advanced microwave oven, which has in its arsenal all the main modes and functions inherent in this type household appliances.

Let me remind you that the test is like: “Plugged into the socket -> it buzzes, spins, the light is on -> it means it’s working!” doesn't suit us! We will check in full - as necessary! We're buying our loved ones for ourselves, aren't we? We don't mind 15 minutes of time, do we? Right? Go!

Checking the appearance of the microwave oven

We carefully inspect the microwave body for dents, scratches and other damage.

We open the door and also carefully inspect the work cabinet. Please note that the cabinet covering must be smooth, without bulges or damage. This is especially true for painted, enameled and antibacterial coatings.

Watch the door close microwave oven. It should fit snugly to the body and not have free movement (do not dangle). The closed door should not be tilted relative to the cabinet opening.

If you find mechanical damage at home, you will not be able to return the microwave oven from the store, because when you issue a warranty card, you will be asked to sign that you have no complaints about the appearance of the product.

Checking the operating modes of the microwave oven

There are four main modes of operation in a microwave oven that require testing for functionality:

• Microwave mode;
• Grill mode;
• Combined mode;
• Convection mode.

For check microwave mode we need a container with cold water. It can be an ordinary jar, glass or cup, the main thing is that it is made of material approved for use in the microwave. Finding such a container in almost any store will not be a problem.

Place a container of water (no more than 200 ml) on the turntable, switch the power regulator to maximum and turn on the microwave for 2 minutes - it shouldn't work! We close the door - now it's working!

While the oven is running, listen to the noise it makes. If you can hear the case vibrating, it means that either the case cover is screwed to the case poorly and without gaskets, or the internal cooling fan is unbalanced and has a lot of vibration. Neither one nor the other is acceptable!

After the allotted time, the microwave should turn off, emitting a signal corresponding to this model.

We take water out of the cabinet - it should be hot. If the specified amount of water is only slightly warm after two minutes of operation, then the microwave oven is not working properly. And under no circumstances believe the seller who may claim that this is how it should be. Even the lowest-power microwave can heat 200 ml in 2 minutes. water until hot.

Grill mode very easy to check.

We don’t put anything in the microwave cabinet, we switch it to grill mode, set the time to 1 minute and close the door.

The hum will be much quieter than in microwave mode, the light will be on, and the turntable will be spinning.

If the microwave oven is new, it will smell like burning machine oil - this is normal! It's worse if this doesn't happen, because... The heating elements of any new microwave have factory grease, which burns when they are first heated.

After turning off, open the door and check whether the grill heating element, which is located in the upper part of the oven cabinet, has heated up. Just be careful - don’t grab the heating element with your hands - it’s hot and you can get burned!

If the model of microwave oven you are purchasing is equipped with more than one grill element, then you need to make sure that they are all in working order.

The combined microwave mode, in which both of the above-described modes are used, does not need to be checked, since we have already checked them one by one.

It remains to be checked "convection" mode- a mode during which the temperature in the working cabinet of the microwave oven is raised to 250 degrees C using a fan and additional heating elements, as in a conventional oven.

I strongly advise you to check if this is true! Of course, it is not necessary to heat up to 250 degrees, but up to 100 degrees will be just right. At the same time, if your microwave is new, then not only the smell of burnt oil will appear, but real smoke. Don't be alarmed, this is normal. Another advantage is that this smoke will remain in the store premises and you will not have to ventilate the apartment. Next time you turn on "convection" mode there will be no more smoke.

Thus, without spending too much time, we made sure that the microwave assistant we selected works properly in all main modes.

If you wish, you can check additional functions, present in the purchased microwave model, if, of course, they are there.

In the majority microwave ovens A high-voltage transformer is used that converts the supply voltage of 220 V into a magnetron supply voltage of about 2 kV. If the oven does not work well or does not work, you need to check the microwave transformer.

In some, usually expensive, models of microwave ovens, the magnetron is powered using a pulse unit, which has less weight, but is more complex. electronic device. In this review we will focus specifically on microwave transformers of the first category of microwave ovens. And the pulse block is a topic for a separate article.

About LG, Samsung, Daewoo ovens

The largest number of cases requiring testing of the microwave transformer occurs in microwave ovens from LG, Samsung, and Daewoo. Perhaps this indicates the poor reliability of these brands of stoves, but most likely this is due to their high prevalence on sale. That is, they are sold in large volumes in the retail chain, which means that the number of breakdowns, which statistically should be the same for all brands, they simply have more due to the shaft.

Symptoms of a problem

The main signs of a microwave transformer malfunction include problems with poor or completely absent heating of products, strong noise when turned on, and foreign odors (overheated insulation or even burning). In such cases, it is, of course, necessary to immediately turn off the device.

High voltage

As you know, food is heated in microwave ovens using ultra-high-frequency waves (or in other words: microwaves). To generate them, a special device such as a magnetron is used. He requires very high standards for his work. electrical voltage, almost 10 times higher than the usual voltage of 220 V, which is available in everyday life thanks to an outlet. The magnetron receives a voltage of this level thanks to a specially designed transformer.

Design

Structurally, a transformer for a microwave oven consists of a stacked core, has three windings, and is flanged. The primary winding is network and receives 220 V power from the outlet. The secondary power winding of the magnetron produces a voltage of 2000 V. And a special third winding produces 3 V for the magnetron filament circuit. From the point of view of the average person, this may seem strange design feature as the output of a high-voltage winding, tightly short-circuited to the housing, and one of the magnetron contacts also has a contact to the housing.

Methods for checking a microwave transformer

First of all, unplug the device from the outlet. Then we disconnect the contact wires from the transformer itself (except, of course, for the body contact of the high-voltage winding). We consistently check the windings for integrity - break or short circuit of the wires. The most common cause of failure is an interturn short circuit. If the continuity test lets us know that all windings are working properly, we move on to checking the performance characteristics.

Method number 1 - direct

The best test mode would be to simply turn on the device at operating voltage. In this case, we would have to get 2000 V on the secondary winding, and 3 V on the filament winding. But, firstly, this requires special caution (in accordance with the PUE, for example, we would have to arm ourselves rubber gloves and rubber galoshes that have passed inspection within the time limits specified by the rules, as well as other protective equipment for reliable electrical safety) and preferably extensive experience. And secondly, not every repairman, not to mention home handyman There is a voltage tester on hand for voltages of 2 kV or more. Therefore, other methods based on knowledge of the basic rules of electrical engineering are more often used. And, most importantly, much more affordable and safe.

Method number 2 - reverse

The most practical, but not the safest way to check the performance is to apply mains voltage to the secondary winding. In this case, we must remove 24.2 V from the primary (220 divided by the transformation ratio of 9.1). Safety measures that must be taken are to carry out measurements on a non-conductive surface. Do not forget that one of the contacts of the high-voltage winding is located on the housing.

Method No. 3 - low voltage

Third method: connecting a safe reduced voltage to the primary winding. For example, 12 V (the source can be a low-voltage power supply). On the secondary we must measure 109 V.

Microwave ovens heat food. Transformer is important element ray-generating chain. This device converts the normal household voltage supplied to its primary winding to the values ​​required for operation at the secondary output. Often it is he who causes equipment malfunctions, so checking the microwave transformer is given Special attention. At independent work it is advisable to use safe way device inspections.

A high-voltage microwave oven transformer is a device consisting of a magnetic core, a frame, one primary winding and two secondary windings. The latter feed magnetron circuits: filament and anode line. The first is made of thick wire, and the voltage at its output is several volts (about three). The second (anode) secondary winding creates an output AC voltage up to 4 kV. The primary winding is supplied with 220 V from the network.

Transformers of microwave ovens produced by various manufacturers differ not only in their appearance: sizes, mounting options. They are produced in different capacities and classes. The output voltage of the secondary windings, the number of turns and the thickness of the wire in them (hence the resistance) are also different.

The secondary high-voltage winding is closed to the housing, as is one of the magnetron outputs.

IN electrical diagram microwaves besides high voltage transformer includes the following elements:

• high voltage capacitor and diode;
• magnetron;
• Limit switches;
• fuse;
• electric motors: platform (turns it inside the microwave cabinet) and fan;
• control block.

In expensive models of furnaces they are used instead of transformers impulse blocks, having a more complex structure, but less weight.

Possible transformer malfunctions and their symptoms

Checking the microwave transformer should be done when this household appliance is not functioning well, or when it is not functioning at all. Symptoms of a problem transforming devices are:

• a fairly strong hum (noise) begins to emanate from the equipment after switching on;
• dishes placed on the platform are not heated at all or only slightly heated;
• During operation there is a smell of burnt insulation.

If such signs appear, it is better not to use the device until it is repaired. In the latter case, it must be disconnected from the network immediately to avoid even greater damage.

It must be remembered that breakdowns with electrical appliances do happen. during power surges supply network. If this happened, then if the slightest hint of a malfunction appears, repairs should be started, during which a manufacturing defect may also be discovered.

The above manifestations in most cases are caused by a number of reasons:

• a break in the wire of the primary or secondary (boost) windings, in both at the same time (a rare case);
• a short circuit between the turns in one of them, or in two at once;
• a break or short circuit in the winding of the magnetron filament circuit.

The transformer magnetic circuit consists of sheets of electrical steel. Noise when the oven is running can also appear as a result of their separation from each other - then it is necessary to change the transformer completely. But this happens very rarely and is easily determined visually.

The vast majority of problems with a transformer are related to its windings.

Procedure for safe inspection

When starting an independent test, you need to stock up on a multimeter (in extreme cases, a two-pole indicator with a built-in power source), screwdrivers with various tips, an ohmmeter, and pliers.

General scheme safe work looks like that:

• disconnect the device from the power supply;
• unscrew the screws and remove the casing;
• discharge the capacitor;
• carefully remove the terminals from the transformer;
• check its windings: if the parameters are normal, replace them and look for other reasons;
• when a break or short circuit is found in them, the device is replaced;
• The oven is assembled and its functionality is checked.

If after assembly the microwave does not function, then you should look for other reasons or resort to testing with the voltage connected.

If, after removing the transformer, traces of insulation melting are visible on its windings, and a strong burning smell emanates from it, then it is no longer suitable for use, and there is no point in checking it. In this case, it will only help device replacement.

Before you begin examining the transforming device, you must make sure that it is receiving power. To do this, you should use a multimeter to check the presence (after turning on the device into the network and starting the heating program) at the connection points of the primary winding of alternating voltage with a value of 220 V. This work is performed with extreme caution to avoid electric shock.

Since to check the transformer you will need to disassemble the microwave oven, this can only be done after disconnecting it from the power supply.

The presence of a high-voltage capacitor capable of maintaining electric charge, leads to the need for it discharges before testing. This is done by simply connecting its contacts to each other (with a screwdriver, pliers) or to the housing when the voltage is turned off.

Methods for diagnosing device performance

The simplest way to check the functionality of a transformer is to replace the existing device with a known good one.

Secure Verification Method

The safest diagnostic method is to check the integrity of the transformer windings with a multimeter. The entire process is performed sequentially. Define measuring instrument(set to certain limits) the resistance of the primary winding and two secondary windings, dismantled and disconnected transformer. If there is a break, the display will display 1. If the circuit is closed, the readings for the primary winding (the device is set to 200 Ohms) should be in the range of 2 - 4.5 Ohms, the filament winding - 3.5 - 8 Ohms, and the high-voltage secondary (switch set to 2000 Ohms) their range is already 140 - 350 Ohms.

If the resistance goes beyond the specified limits, this indicates the presence of an interturn short circuit.

When taking measurements, you need to take into account the value of your own multimeter errors. It is determined by short-circuiting its probes to the limit used. The value given will be an error that must be taken into account.

You can either check the transformer in the microwave yourself with the device, or entrust this task to professionals from the workshop. The first case will require knowledge of the basic fundamentals of electrical engineering and some working skills.

Live tests

When the measurement results match regulatory indicators, but the oven does not work, to make sure that the transformer is working, you need to check its performance characteristics.

A dangerous option is to measure the output voltages of the secondary windings. The actions are performed in the following sequence:

• the oven is supplied with 220 V power;
• The tester checks the voltage at the output of each winding: for the high-voltage winding it will be about 2 kV, and its value at the filament winding will be around 3 V.

In addition to observing safety precautions, this method requires equipment capable of measuring alternating voltages greater than 2000 V.

It is safer to use the following methods.

1. Reverse verification method is carried out by applying 220 V to the boosting secondary winding, and the output of the primary should be about 24 V (the average transformation ratio is taken to be 9.1).
2. You can power the primary coil with 12 V (from a low-voltage transformer or power supply), then the secondary should be approximately 109 V.
3. Also, a short circuit between the turns is present if the transformer device heats up at idle.
4. If it gets hot under load during secondary circuits, and after it is turned off it stops, then the reason should be sought further in the diagram.

The choice of method for checking a microwave transformer at home depends on personal qualifications, knowledge and skills, and available tools. The safest option is a regular test to determine the integrity of the circuits or the presence of breaks. The use of 220 V voltage when determining the operability of a device requires strict compliance with electrical safety measures. When there is uncertainty about your own capabilities, it is better to seek the help of professionals.

Author: elremont from 4-08-2015

In this video you will learn how to test a microwave oven transformer, capacitor, high voltage diode, ceramic power fuse, micro switches and magnetron.
You can watch my other microwave oven repair video here:

http://rutube.ru/video/994e2b4e1ef3c69f301aaaeec7d1f8e3/ (step-by-step troubleshooting of a microwave oven within a few minutes)
DISCLAIMER: This video is not responsible for any damage or injury due to inept, negligent, unqualified or negligent individuals. If you do not follow my instructions carefully, are unable to take the necessary precautions, or doubt your abilities, then you should not study with me. repair work in the microwave. All at your own peril and risk.
Thank you for watching!
***If you enjoy watching my videos, please show your support by subscribing, linking to my videos on other sites and blogs, hitting the thumbs up button and watching my video playlists. This helps to make more videos in the future. (Views are required to keep the channel active) ***

In this video, I will show you how you can check the components of your microwave oven if your oven is not working as it should.
Now here at the back we have the microwave transformer. We'll check the transformer.
And these small transformers are installed on the control module. I'll show you how to check them if your display isn't working. When the microwave is plugged in but nothing is working, you should at least be able to see the clock and digital display.
If this does not happen, then you need to check the fuse. The first step before working on your microwave is to unplug it from the outlet before you remove the metal cover. It is usually screwed on at the back and along the bottom edge.
*If your display does not work after the capacitor has discharged, you can skip to 14:40 in the video*
Once you have unscrewed the lid, lift the back of the lid and remove it from the microwave.
Now, once you open it, the most important thing to do to avoid fatal injury is to find the high voltage capacitor. And two of them are right here, they look like this. Okay, and they are usually located near your high voltage diodes.
Now, once the unit is disconnected and you have found the capacitors, you should discharge those capacitors before doing any tests. To discharge, we take this tool that I made, it is a 20K Ohm resistor. And I connected an alligator jack on each end.
*You can buy a 5 or 10W high value ceramic resistor from Radio Shack, or you can salvage one from an old TV*
We take a regular Phillips screwdriver and attach this clamp to the screwdriver, like this.
We place the other end of the clamp on the metal chassis of the microwave oven. Once one clamp is attached to the metal body of the oven and the other end is connected to a screwdriver, you need to touch the capacitor contact and hold it there for maybe five seconds. Let's go to the other side and touch the other contact.
Now, once the resistor has touched each terminal for about five seconds, the next thing to do to confirm that it is indeed discharged is to grab some good insulated pliers. We unclench them, and then put one end to this contact, and the other to the other and hold it there. If you see any spark, it means it has not been discharged, you need to keep the contacts closed for a minute and then you can move on.
Once you are sure that the capacitor is discharged, take electrical tape and wrap it around all the wires in this contact to ensure that you do not mix them up later.
When you put them back, it makes no difference, one way or the other. It is not polar.
You can just put this contact and this contact. There is usually a resistor inside the capacitor that resets the voltage immediately when the microwave oven turns off.
As you can see here in the diagram there is a capacitor symbol at the bottom and right above it it says "10 megohm resistor"
Also, you discharged this with the resistor you have, it already has a resistor built in. Now, once the capacitors are discharged, it is very easy to check that they are working as they should. Set your meter to measure a low resistance value, in my case 200 ohms. Connect one contact to the first probe of the multimeter and connect the second probe to the other contact of the capacitor. You should not see any reading unless the capacitor is shorted. So that's a good sign.
Now disconnect one wire from the capacitor, set the meter to the 20 MΩ range or higher, and then check the resistance between the capacitor contact and its body. The resistance should be very high, there should be no readings.
Now I will check the resistance on the case. Nothing. Now move this wire to the other pin. Clean the body. Nothing. You have just verified that the capacitor is good.
*Also measure the resistance between terminals 2 at the maximum resistance range setting. This value must be equal to the resistance value for discharging inside the capacitor. If it is less, the capacitor may be faulty *
Now you need to make sure that the capacitor is not puffy, so it could explode when you look at it. Make sure there are no leaks and the capacitor is not showing any signs that it is about to explode. If it is swollen, but passes the test, then the capacitor still needs to be replaced... The next step is the diode of your microwave oven. There are now two ways to test a microwave diode. Now let's set the device to the measuring range of 20 volts.
*Lower voltage range direct current *
We take our digital multimeter, black probe, this is ground or minus, connect it to where the line is drawn on the diode. You can see a triangle pointing towards the line and you need to make sure that the black probe is connected to the bottom where the line is. We'll take the minus from car battery while the engine is running, and connect it to the same place where the negative probe of the multimeter is connected. Now let's take the plus from the car battery and connect a resistor to it.
You can use a 1k resistor. or 500 Ohm.
*You can find them in broken electronics*
Ideally, 1k ohms is best, but you can go lower, like 500 ohms, if that's all you have. We will connect the positive from the battery on one side, then connect the other end to the diode, making sure everything is secure. This end here is marked as a triangle pointing towards the line. Thus, we connect the plus to the end where the triangle is, and then the minus where the line is. So we connect the plus from the battery through a resistor to the diode.
Now, use a probe to connect the jumper and connect everything together. Thus, we make a junction between the resistor and the diode, there is no need to put the connector on the positive side, you need to put the resistor and diode in series. The diode will usually have a voltage between 6.5 and 10 volts. And we have about 6.5. Now, once you have completed this test and have determined that the voltage is between 6.5 and 10 volts, you can do another test to confirm that the diode is good.
To do this, set the multimeter to the highest resistance measurement limit. Many multimeters only have a limit of up to 20 megohms. Some up to 2000. If you have a limit of 200, that's very good. Set it to 200. In my case I have a limit of 2000.
* During this test, do not touch the probes of the device with your fingers *
Set the device to maximum settings. Place the probe on one end of the diode...
* Test is carried out on plastic, glass, granite or any other non-conductive surface *
And we put the other one on the other end. Then you can see we have 37 mega ohms, 35, 36. That's good. Now we'll take the yellow one and swap the probes. Now the reading should be much higher somewhere between 180 and 350. Okay. So now, as you could see, in one direction the resistance is between 20 and 50 mega ohms, and in the other direction it is 280. This check and voltage test confirmed that this diode is good.
Now, to check the magnetron, you need to look at it and make sure that there are no cracks on it, especially on the magnets. One here and one in front. Make sure they are not cracked. Look all around. Shake it, make sure there are no rattling noises. Check here. This white part around, make sure there are no cracks. We will check the resistance between these two pins. It should be very small, about 0.1 Ohm. But there shouldn't be a zero. There should be a small resistance, usually 0.1. So I'll set the multimeter now to the minimum resistance range of 200 ohms. We connect the black probe to one contact. I take the red probe and connect it to this connector... Okay. We get 0.6. But you should also understand that the resistance is a little higher because I connected through several jumpers. If I check directly from the device it will be around 0.2. So as long as you see readings of 0.1, 0.2, 0.3 then this is normal.
Next, let's check the resistance between the contact and the magnetron body. We will disconnect one of the multimeter probes from the magnetron, and switch the multimeter to the 20 mega ohm range. When I touch the probe to the magnetron, you should not see any numbers on the multimeter. Now let's remove this probe and switch it to the opposite contact. Do it again.
If the tests were successful, then the magnetron is good and you can connect power to it. Now let's check the high voltage transformer. Okay, before testing the transformer, you also need to do the marking procedure. Place a piece of adhesive tape next to "1". And here you can put a “1” with a marker. And here is 2. Disconnect the wires.
*Actually there is no difference for a 120v winding, but still good practice, do not allow rearrangement of wires*
You need to check the resistance between these two contacts. This should be done on the lowest range at -120. Take the device and connect it to one of the contacts. Take another probe and connect it to another contact; the resistance should be about 1 ohm. But there shouldn't be a short circuit. Seeing zero is not good. You see, 0.5 0.8, 0.7. This is fine. Now let's leave one contact connected, disconnect the other probe of the device, and we will set the device to the 20 mega ohm range.
*Make sure you have cleared metal surface on the transformer frame. The core is varnished *
The varnish on the transformer body must be cleaned. And you should not see the device readings. Now let’s move the probe of the device to another contact and check that there are no readings there either. We have made sure that the primary winding is ok. Now to check the filament secondary, high voltage secondary, you need to mark the connections before disconnecting them, just like you did with all the other components. And let's look at these thick wires. This is a coil, these two red wires come from it. We'll check it first.
*Filament winding*
And we will do it the same way as before. We will set the multimeter to the low measuring range and connect one probe here. And we will connect another probe to this end. And as you can see, you get low resistance again. 1 ohm or less is usually normal.
Check that there is no leakage between one of these wires and the core, so we'll set the range to 20 megohms again, leave one probe connected to one of the wires, and then with the second probe you touch the core, there should be no reading on the meter. Put it back and then we'll do the same thing. Now one probe right here on the high voltage winding, we want to check this contact between the wire coming from the coil with the wire of the big coil here, and measure the resistance between this point and the body. So I'm going to take one of my DMM wires and plug it in there. I will set the device to the 200 Ohm range. We measure the resistance of the high voltage winding, 95 Ohms. The typical range is between 80 and 120. We have just verified that the transformer is good.
The fuse is now located where the power cord attaches to the board surge protector. On this small board there is a toroidal ring that looks like a donut with a wire wrapped around it and we will find this fuse. And you won't be able to tell if it's burnt or not by looking at it because it's ceramic, so the only way to test the fuse is to use a DMM rig to test for continuity. Short your probes together. This is a simple test. Press the test leads onto each side of the fuse. And this is a good fuse. If it burns out, it must be replaced.
The oven also has these microswitches. This switch has two contacts. When the switch is pressed, the circuit is closed; when not pressed, the circuit is open. We disconnect one wire from the switch, and then set the DMM mode for checking conductivity and attach the probes to the contacts. Click it, make sure it works. If it works fine a few times, then the switch is good... You may see another type of switching like this one. These are "general", "normally open" and "normally closed". Therefore, when you press the button one pair should be closed and when you release the other pair should be closed. This is how it is checked.
Okay, I unplugged the connector. It's easy to pull off. To check, look at the inscriptions on the contact, look for where it says “Com”, the bottom one says “Com”. Attach one of your probes there and take another probe and to check the continuity, connect it to the contact, press the button. This one works great.
Now this contact here should be closed when I connect the tester. And when I press the button the contact disappears. Make sure you check all three switches. Sometimes there are four, make sure the wires are connected well, if they don't work then the microwave won't work.
The last component is the transformer installed in the module, so if the fuse is good and power is getting to the board but the display is not working, then there is a high probability that the transformer is faulty. They are all very similar. It has three pins on one side and four on the other. And although there are three, only two are used, you have to look very close to see where the wires are connected.
*The side with fewer pins is 120V power*
Let's see, there's one wire going to this pin, and you could see a black wire there going to the second pin. And the last contact is not used. Now for this test we set the multimeter to a higher value of 2000.2k. We attach one probe on one side of the winding, and the other probe on the other side.
And we have 400 Ohms. These are normal readings. Switch the device to the measuring range of 20 MOhm. Setting it to 20 MOhm, we check the resistance from the contacts to the core. Make sure there is no resistance between them. I'll do it right now. Remember, before doing this, you must scrape the varnish off the core down to the metal, otherwise you will not be able to get normal readings. We must touch the core and contacts, and must not get any readings. Then you need to do the same on the other side, you need to touch the core again, the place that has been stripped down to metal, and you should not see any readings. The primary side is good. Now....
This transformer has two sets of windings on the secondary side. On these two ends the output is 11 volts, and on these two the output is about 5 volts.
Thus, it is necessary to check two windings. To test the secondary side, there are two sets of windings. In this case, the two pins on the right are 11 volts, and the two pins on the left are 5. We need to set the device to the 2k range and put one probe on one wire. One probe on one side of the winding. I'll touch the other one... And we have 12 ohms, that's good.
Now back to the 20M range again and you should touch the transformer core and you should get no reading at all. Do the same for the other pin, making sure there is no reading on it either. Now you can check the other winding, switch the device back to 2k. One probe on this pin on the right and touch it on the left... Press it on the left and I get 4 ohms. So it's okay. Let's go back to the 20 megaohm range. Now let's look from one pin to the core, you should get nothing. And then move the red one here and check that there shouldn’t be anything before the core either.
_

With a working control circuit, troubleshooting should be carried out as follows:

1. Check the serviceability of the high-voltage transformer.

The transformer converts the alternating voltage of the network into two voltages - the filament voltage and the anode voltage of the magnetron.
Disconnect the terminals of the secondary windings of the transformer from the circuit and check their integrity. Connect the primary winding to the network. The transformer must remain cold when idling. Make sure there is a filament voltage, which is about 3...6 V, and an anode voltage (measured between the transformer body and the high-voltage terminal, which is a double-insulated terminal), which is 1.5 - 3 kV. Be careful when measuring anode voltage!!! Do not bring the high-voltage terminal closer to the oven body. If there is no anode voltage, make sure that the high-voltage fuse located at the high-voltage terminal of the transformer is working properly. If the fuse is defective, replace it with an equivalent one. high voltage fuse.

2. Check the serviceability of the protective (2X062H) and rectifying (HVR-1X) diodes. The protection diode should not ring in both directions. The rectifier should ring in one direction at the resistance measurement limit - 1 MOhm. It is advisable to use an analog device (measurement limit kOhm * 100). The approximate open resistance is about a megaohm.

3. Check that there is no short circuit on the high-voltage capacitor both between the terminals and on the housing. It is advisable to check with a megometer (with a test voltage of 500-1000V)

3. After making sure that the transformer, diodes and capacitor are in good condition, check the integrity of the magnetron heater (connected to the terminals on a plastic insulator, it sounds like a short circuit) and the absence of a short circuit between the magnetron terminals and the housing. A magnetrom is an electric vacuum microwave device made with a directly heated cathode, i.e. the cathode is connected inside the housing to a heater. The anode is the magnetron housing.

4. Restore connections in the high voltage part of the oven. Turn on the oven. If there is no heating, make sure that all voltages are supplied to the magnetron terminals. Be careful, anode voltage is life-threatening. The filament circuits are under anode voltage. The filament current is about 3 A. If all voltages are present, the magnetron is faulty.

Regards, Alexey.