What is a capacitor, types of capacitors and their designation on diagrams. Replacing magnetron feedthrough capacitors
Microwave oven is composed of many parts that actively complement each other’s work. Failure of one component leads to the termination of all components. One of the main components is a magnetron. If the microwave oven ever malfunctions it is the capacitor that is the first to be checked. Heating and cooking in the microwave oven is done by the radiation emitted by the magnetron.
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Principle of the device
A capacitor is a device that has the ability to store a certain charge of electricity. It represents two metal plates set in parallel, between which there is a dielectric. The increase in the area of the plates increases the stored charge in the device.
There are 2 types of capacitors: polar and non-polar. All polar fixtures are electrolytic. Their capacitance is from 0.1 ÷ 100000 uF.
When testing a polar fixture, it is important to observe polarity, where the plus terminal is connected to the plus terminal and the minus terminal is connected to the minus terminal.
It is the polar capacitors that are the high voltage ones, the non-polar capacitors have the small capacitance.
Microwave with indication of capacitor location
Microwave magnetron power circuit includes diode, transformer, capacitor. Through them to the cathode goes up to 2, 3 kilovolts.
The capacitor is a large part weighing up to 100 grams. A diode lead is connected to it, the second one is on the body. A cylinder is also placed near the unit. Specifically this cylinder is a high voltage fuse. It must not allow the magnetron to overheat.
Microwave high voltage transformer.
High voltage transformer supplies power to the magnetron of the microwave. If the step-up transformer fails, the high-voltage part of the device does not receive power, the microwave oven stops generating microwaves and heats products accordingly.
Inter-voltage short circuit.
The most common cause of transformer malfunction is an inter-turn fault, due to the destruction of insulation due to overheating. Visual signs of inter-turn transformer short circuits are a strong darkening of the high-voltage winding of the transformer, traces of carbon.
Microwave oven is working with a loud buzzing noise and a smell of burning, while the transformer winding is strongly heated.
Visible signs of a faulty transformer
To prevent such malfunctions, it is recommended not to overheat the microwave, after prolonged work let it “rest” for about 15-20 min. so that it can cool down.
Contact burned on the connector.
A common cause of faulty transformer is the lack of contact at the connection point of transformer terminals and connectors. This is caused by badly crimped connectors. The bad contact area starts to spark, the contact surface of the connector gets very hot and burns out, eventually the contact disappears altogether. The consequences of poor crimping of connectors are shown in the photo.
Breakage in the place of connection of the terminals to the winding.
If there is no visible damage to the transformer, but it does not work, perhaps there is a loss of contact at the point of connection of the winding with one of the terminals. This happens quite rarely, mainly due to poor quality factory soldering.
Diagram of a UHF transformer
The microwave power transformer has a 220 volt primary winding and two secondary windings, one of them increasing from 220 volt to
2000 volt, necessary to power the high voltage circuit of the magnetron, the second lowers from 220 V to
3.1 V, the so-called “incandescent winding”, is necessary to power the anode of the magnetron.
How to test a high voltage transformer with a multimeter
The presence of contact can be checked with an ohmmeter. To check the connection it is necessary to “test” the resistance of its primary and secondary and incandescence windings. Before making a measurement, all terminals must be disconnected from the transformer.
Check primary winding: 2 to 4 ohms. In this case, the terminals of the primary winding must not ring on the transformer body. If there is a breakdown of the primary winding to ground, the transformer is defective.
Checking the secondary winding: 120 to 200 Ohm. One of the leads of the secondary winding is fixed to the transformer body, so when “testing” the secondary winding one of the tester probes touches the metal body of the transformer and the other one touches the terminals of the secondary winding.
Check the filament winding: 0.1 to 1 Ohm. If the incandescent winding is intact there should be no interruption.
Microwave transformer replacement
To replace a faulty high-voltage transformer you need to find a similar part. Microwave transformers have a common principle of operation, but they differ in class (see marking 200, 220, 250 class) capacity and location of mounting fasteners. The power of the transformer must be coordinated with the power of the connected magnetron.
If the power of the new transformer will be less (100-200 watts), then the oven will be a little underheated, you need to increase the heating time. If the power is more. nothing terrible will happen, a little increase in power reserve and, accordingly, the life of the transformer.
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How to check for malfunction
Replacing the part is expensive, so many people prefer to buy a new microwave. But don’t get rid of your old appliances. Check the magnetron of the microwave oven for malfunction to make sure it is broken. The main signs of malfunction are smoke, sparks, and sounds from the oven. If not, do a general check or diagnosis with a tester.
Unplug the microwave from the electrical outlet. Unplug the power cord. Visual inspection of internal compartment of the oven should reveal melted, burned, or darkened areas. This is a good way to find a blown fuse. If you don’t see anything, you can’t do without a meter.
Checking with a tester
Hidden faults can be detected by testing the magnetron with a tester. Diagnose the part not connected to the microwave.
- Connect the tester probes to the terminals of the magnetron. If filament is burned out, infinity will be indicated.
- Inspect the main circuit board, in which diodes, resistors, varistor, etc. are built in. Do not unsolder any components to check, you can do the test directly on the board.
- If the thermal fuse is tested at room temperature, it should give a signal.
- High voltage capacitor only tested for breakdown. In its normal state it shows infinity. In defective. resistance close to zero.
- Diagnosing a High Voltage Diode. Diodes connected in series make it impossible to inspect it. Internal resistance level is high for measurement. Make sure there is no breakdown in this part. A megohmmeter will help.
Check the rectifier diode and the stabilitron
A protection diode and also a rectifier (including a power diode), or a Schottky diode can be checked with a multimeter (or with an ohmmeter) by putting it into the continuity test mode, like the one in the picture.
Connect the probes of the measuring device to the pins of the radio element. At connection of red wire (“”) to anode, and the black one (“. “) to cathode, the multimeter (or ohmmeter) display will show the value of threshold voltage of the diode being tested. After reversing the polarity the instrument should show infinitely high resistance. In this case it can be stated that the element is serviceable.
If the multimeter detects a leakage when connected backwards it means that the radio element is “burned out” and has to be replaced.
Note, this testing technique can be used to test diodes on the vehicle’s alternator.
The test for a diode is done in a similar way, but it does not allow us to determine if the voltage is stabilized at the required level. So we have to build a simple circuit.
- make the circuit assembly;
- set the multimeter mode, which allows to measure DC voltage up to 200 V;
- switch on the power supply and begin to gradually increase the voltage until the ammeter on the power supply unit will show that the current flows through the circuit;
- connect a multimeter as shown in the figure and measure the stabilization voltage.
If the magnetron has the same problem as the first, it should be replaced, and the high-voltage diode should also be checked to see if it is working properly. When the magnetron is in a fault, usually the diode is also in a fault.
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How to check the magnetron using a multimeter As we know, repair of any electronic equipment is not cheap, and sometimes it can even exceed the cost of buying a new device. Ask me, I am available!
Vitek microwave. How to check the magnetron | Radiobrain
Unlike ordinary diodes, a varicap has a p-n junction that has a non-permanent capacitance whose value is proportional to the reverse voltage. Checking for open or short circuits for these elements is done in the same way as for normal diodes. To check the capacitance you need a multimeter with a similar function.
For the test you need to set the multimeter to the appropriate mode as shown in the picture (A) and plug the part into the connector for the capacitors.
- Resistors: R1, R2.120 kOhm (yes, two resistors, yes in series, no one can replace one, parasitic capacitance, no further Комментарии и мнения владельцев); R3. 47 kOhm; R4. 100 ohms.
- Capacitors: C1. 0,15 uF; C2. 75 pF; C3. 630 pF; C4. 47 uF of 50 volt.
This version is not perfect, the need for its practical application is questionable, but the scheme clearly shows the dependence of the varicap capacitance on the nominal voltage.
How to check the capacitor microwave multimeter
As we can see, because of the specific assembly, you can not measure such a diode with an ordinary tester. To check it, the element should be turned over, so as to measure from two directions. To check the diode for serviceability, you need to do the following manipulations:
- Disconnect the microwave from the mains;
- Disconnect the diode from the circuit;
- Connect the circuit element to the lighting circuit. For this purpose it is necessary to use a small incandescent lamp for about 15 V on 220 V line.
Please note! The incandescent bulb should burn at half its brightness and it should flicker clearly.
This circuit should be powered from a 220 V mains supply. There is also another way to check if the diode is working properly. Here, too, an incandescent bulb is used and the principle of verification is very similar:
- connect the element to be tested to a 20 V incandescent bulb;
- If the diodes are connected in the same direction, the light bulb will burn at half voltage (faulty element);
- After that we turn the diode.
A change in the glow is an indication that the element is “punctured” and should be replaced. In addition to the above options for checking there is another method to make sure that this
Microwave component. For this you will need a charger from a mobile device or tablet. Here you will also need a rheostat. Please note! Chargers for tablets and cell phones have a voltage of 5V. In this situation, the check involves the following manipulation:
Before checking the capacitor
Before starting the test, the capacitor should be inspected. If it has cracks, insulation failure, leaks or bloating, the internal electrolyte is damaged and the device is broken. It must be exchanged for a working device. If there is no external damage, you will have to use a multimeter.
Before taking a measurement you need to determine whether the capacitor is polar or nonpolar. The polarity of the first must be obeyed, otherwise the device will fail. In the second case, the determination of the plus and minus outputs is not required, but the measurement will be carried out using a different technique.
You can identify the polarity by the marking on the body. On the part must be a black stripe with the zero marking. On the side of this leg is a negative contact, and on the opposite side is a positive contact.
How to check the capacitor with a multimeter When checking with a multimeter we do not need to measure the capacitance of a non-polar capacitor, it is enough to measure its resistance, it must be infinitely large. Ask me, I’m available!
Types of high voltage transducers
Elements of the converter installed in the microwave oven:
The primary winding receives U = 220 V. The filament is energized from the secondary. The first of the two secondary windings is made of a wire with a large cross section. U output is approximately 3 V. At the output of the second winding. high alternating U = 4 kV.
Microwaves of different brands use converters of different manufacture. The transducers don’t look the same and have different specifications. They differ in:
- The output voltage of the secondary windings;
- the number of turns in the coils and the cross section of the wire;
- the method of attachment.
The secondary coil, like one of the outputs of the transmitter, is shorted to the body.
Faulty diodes with a multimeter is easier to find and easier to determine the cause of the failure of your device.
Modern multimeters are able to handle different kinds of currents:
The most popular on today’s market are digital devices.
But you can also find analogue devices on the market.
Both are often used at home.
But the digital ones are more accurate (with an accuracy of 0.5%) and are easier to wire.
Analog multimeters have higher reliability and lower cost. But they are less accurate. error 1.5-2 %.
Checking the capacitor
Today microwave ovens are common appliances used in the home. During the operation of microwave oven there are cases when it is necessary to check whether the capacitor works. This need arises when you suspect that the oven is not working properly and malfunctions. Such a test can be performed with your own hands, without the involvement of specialists
But it must be done very carefully, so as not to accidentally damage other elements of the microwave. How to properly test the device?
How to find the capacitor in the microwave
The first thing to do if there is any manipulation with the capacitor is to disconnect the microwave oven from the mains in order to avoid the negative effects of electric current on people. Next, you need to unscrew the back cover of the microwave and remove the panel that covers the device. Find the part is not difficult, if you know what it is by its appearance. It is usually located near the transformer.
Even though the microwave is unplugged, there is a risk of electric shock because this part stores it (up to 2 kV). Therefore, the appliance must be discharged. To discharge it, you need to short-circuit its terminals with something, like a screwdriver. This is the most common way, but it is considered unsafe for the device itself. Only after discharging the appliance can it be used for any kind of manipulation. Personal safety comes first!
Using a multimeter to check
You can check if the capacitor is operational by means of a light bulb with a power of 40 W or more. If the lamp does not light up when you touch the leads to the terminals, but there is a spark, then the device is in working order. If you attach one wire to the terminal of the capacitor and the other wire to its case, you can check the case for breakdowns. If no spark is detected and the light bulb does not illuminate, the instrument is in working order. If there is sparking or the bulb is on half light, then the part is not working. This method can be used if you do not have a multimeter handy.
For a more detailed diagnostics of a capacitor a special device, a multimeter, is used. It is designed for testing devices and their individual components. This device has two modes: multimeter and ohmmeter. In “multimeter” mode the device operates at a small voltage. In this case, the device will only indicate the absence of a breakage, or the presence of a short circuit (short circuit). For a detailed check switch the tester to the “ohmmeter” mode. To test the capacitor in this mode it is enough: to remove the cover, to remove the terminals, then to discharge the device, to switch the device into the “ohmmeter” mode (resistance = 2000 kOhm), then to check the terminals for absence of defects (because bad contact affects the reliability of measurement) and finally to connect the terminals to the component.
Precautions for checking electrolytic capacitors.
When testing an electrolytic capacitor it is necessary to discharge it completely! Especially this rule is worth following when testing capacitors with high capacitance and high operating voltage. If this is not done the measuring instrument can be damaged by high residual voltages.
For example it is often necessary to check the functionality of capacitors that are used in switching power supplies. Their capacitance and operating voltage are high enough to damage a multimeter in case of an incomplete discharge.
Therefore it is absolutely necessary to discharge them by short-circuiting the leads before testing (for low-voltage capacitors with low capacitance). This can be done with a normal screwdriver.
Capacitors with a capacity of more than 100 uF and operating voltage of 63V is desirable to discharge through a resistor with a resistance of 5-20 kOhm and a power of 1. 2 Watts. For this purpose connect the pins of the resistor to the pins of the capacitor for a few seconds, in order to remove the residual charge from the terminals. Discharge of the capacitor through the resistor is used to avoid the appearance of powerful sparks.
When performing this operation do not touch the pins of the capacitor and resistor with your hands, otherwise you can get an unpleasant electric shock at the discharge of the terminals. It is better to clamp the resistor in insulation with pliers and then connect it to the pins of the capacitor.
When you short-circuit the pins of a charged electrolytic capacitor a spark can fly through, sometimes very strong.
Therefore, care should be taken to protect the face and eyes. If possible use protective glasses or keep away from the capacitor when carrying out such work.
How to test a ceramic capacitor with a multimeter
Ceramic elements are usually without polarity. As we have already mentioned, their check is almost the same, the only difference is the norm of the values obtained:
If you see a value of 2 Mohm or more on the display. everything is fine. If the value is lower, the capacitor is not suitable for further use.
Now you know the most important thing about how to check the health of a capacitor with a multimeter and you can do it yourself.
Question: How can you test the capacitor with an ordinary multimeter?
Answer: First you need to discharge the capacitor and also to determine its type: if it is polar, you must observe the polarity. If it is non-polar, it is not necessary to identify the “-” and “-” outputs. You also need to unsolder the capacitor.
Question: How to test the capacitor with a multimeter?
Answer: You need to select the siphon mode, touch the pins of the capacitor with the feeler and listen attentively. The multimeter will emit a short beep.
Question: How to test the capacitor with a simple multimeter, without unsoldering it?
Answer: If you leave the component on the board, the results will be inaccurate. Without unsoldering you can only check whether the capacitor works or not, if it is not shunted by a low impedance circuit. You need a constant voltage or resistance test mode for that.
Question: How to properly test an electrolytic capacitor with a multimeter?
Answer: electrolytic or polar capacitor is tested in the ohmmeter mode or in the capacitance measurement function. In the first case we choose the ohmmeter mode, set the measuring range (200 Ohm) and touch the capacitor terminals with the stylus depending on polarity.
Question: What is the best way to test a run capacitor with a multimeter??
Answer: For this you need to de-energize the air conditioner, discharge the capacitor and remove the terminal. On a multimeter you select the capacitance measurement mode. Also select the value limit, depending on what is indicated on the case. The terminal is removed, the probes are connected to the capacitor pins.
The value is calculated with the capacitor’s ability to store energy equal to 1 coulomb, at a voltage difference of 1 volt between the 2 plates. If you don’t understand something, write to me!
How to check a capacitor with a multimeter: instructions, photos, videos
Checking the different types
Checking a capacitor with a multimeter for resistance
When testing a ceramic capacitor (non-polar) with a multimeter different dielectric materials are used. For example, it could be paper, glass or air.
The process of checking a capacitor with a multimeter on the photo
If the device is working, it will show a value of 2 Mohms. If the indicator will be less, then the device is out of order.
Checking a film capacitor with a multimeter, check the resistance value. If there is a “leak” in the device, then nothing will change. If there is an internal breakage, then on an analog multimeter the arrow will go to infinity.
If a multimeter is to be used to check the starting capacitor for proper operation, first remove the starting mechanism. Then check it for electrical leaks. Connect the probes to the terminals. After that the capacitance is checked.
When it comes to checking a non-polar capacitor, you should refer to the material provided above, because in terms of the principle of this type of device is no different from a ceramic capacitor.
The smd capacitor is checked in the same way as a normal device. By measuring the maximum resistance value.
Warning! Checking a high voltage capacitor it is only necessary to charge it more than normal. Then everything is immediately noticeable.
The AC capacitor is tested with a multimeter by measuring it twice, with reversed polarity. Then they are compared and a conclusion is drawn from this. If the reading is higher, then the unit is serviceable.
Microoven Capacitor wiring. After Problem smoke inside microwave
Now you know the most important thing about how to test a capacitor with a multimeter and you can do it yourself. If there is anything you do not understand, write to me!
To check if the high-voltage converter is working properly, you need to arm yourself with a multimeter, and you will also need a multimeter:
- turn the unit off. remove the plug from the socket;
- Loosen the screws and remove the cover;
- Discharge the capacitor;
- remove the terminals from the transformer;
- check the coils with a tester. if there are no deviations, they are put back;
- if damage is found. a wire is broken or a short circuit occurs, change the device
- assemble the heater and check its operation.
If the unit still does not function after taking these actions, continue troubleshooting or check the unit when it is energized.
A transformer showing signs of burned-out insulation and emitting a burning odor needs no further inspection: it is broken and cannot be repaired.
A high-voltage capacitor easily stores a huge electrical charge, so it must be discharged before measurements. How to do this? Just short-circuit its contacts, this can be done for example with a pair of pliers.
Measuring the capacitance in the resistance mode
Set the switch on the multimeter to resistance (ohmmeter) mode. In this mode it is possible to see, if there is a breakage or short circuit inside the capacitor. To test a non-polar capacitor, set the measuring range to 2 megohms. For a polar product a resistance of 200 ohms is set, because at 2 megohms the charging will be fast.
The capacitor itself should be unsoldered from the circuit and placed on the table. Touch the pins of the capacitor with the stylus of the multimeter and observe the polarity. In a non-polar component, it is not necessary to observe the plus and minus.
When the pliers touch the pins the value will appear on the display and the value will increase. This is because the multimeter will charge the component. After a while the value on the screen will reach one. it means that the device is in good order. If 1 immediately lights up when testing, there is a breakage inside the device and it must be replaced. A zero value on the display indicates that a short circuit has occurred inside the capacitor.
If a non-polar capacitor is being tested, it should be above 2. Otherwise the device is not functional.
The above described algorithm is suitable for a digital tester. When using an analog device, the test is even easier. you only need to observe the movement of the arrow. The probes are connected in the same way, mode. resistance test. If the arrow moves smoothly, that means that the capacitor is in good order. Minimum and maximum values when connected indicate that an electronic component is broken.
It is important to note that the ohmmeter mode test is for parts with a capacity greater than 0U25 uF. For smaller values, special LC meters or high-resolution testers are used
Electrical part of the circuit
Before proceeding to the diagnosis of the furnace malfunction, let’s look at the circuit diagram, which directly affects the operation of the magnetron.
As we have already found out, the magnetron is primarily responsible for heating, which is essentially a vacuum diode, the anode part of which is a vacuum tube with sections. On the sides there are magnets that create the magnetic field and set the trajectory of the particles. In the central part of the magnetron is the cathode, inside which is the filament winding (heater), which is responsible for the emission of electrons.
For operation of the anode of a magnetron a high voltage (2-4 kV) is required, which is provided by a step-up high voltage transformer.
On the primary winding of the transformer comes the AC voltage of 220 V. From one of the secondary windings, a filament winding voltage of 3.15 V is applied. The other secondary winding, together with a voltage multiplier, made on a high-voltage capacitor and diode, delivers DC voltage to power the anode of the magnetron.
The diode in the circuit is included so that it closes at the positive half-period. At this time the capacitor starts charging. At the negative half-period, the diode is opened and the voltage is applied to the magnetron together with the accumulated capacitor charge.
In order to quickly discharge the capacitor, a high resistor is built into its housing. There is also a fuse diode (protection diode) in the circuit, which protects the transformer from overheating in case of a short circuit in the magnetron or an overvoltage increase on the capacitor.
There is also a fuse in the magnetron power supply circuit, which protects the transformer.
In addition to these elements, there is a thermal fuse which monitors the temperature of the magnetron. When the magnetron overheats, it opens the circuit, and the magnetron stops working.
So we have found out that 220 V AC voltage comes to the primary of the high voltage transformer, and since the transformer is step-up, the voltage on the secondary winding is already 2 kV. Then the voltage is multiplied by a factor of two, thanks to the capacitor and the diode. From 2 kV voltage is increased to 4 kV and fed to the magnetron anode.
Let’s proceed with the diagnosis of our power circuit. It is not worth talking about a specific model, for the reason that all microwave ovens are built according to the same scheme.
We open the case, take a multimeter and check if the voltage comes to the primary of the high voltage transformer. If the voltage is normal, then we go further, if the voltage is below 200-210 V, then the cause may be it. With such voltage magnetron can not resonate, it lacks voltage and starts to heat little. And if the voltage is even lower, it may not work at all.
If it is not the undervoltage, unplug the microwave and check the high voltage part. But before that, don’t forget to discharge the high voltage capacitor.
First of all we pay attention to the reliability of the contact connections, since this is often the cause of malfunctioning. Then we put a multimeter on the continuity test and check the fuse, usually located in a plastic case.
If the fuse is intact, check the high voltage diode and the high voltage capacitor one by one.
The high voltage diode consists of a number of ordinary diodes connected in series. That is, you can’t check it like a normal diode. But it is possible to diagnose it approximately. set the multimeter to 200 megohms resistance (but not every multimeter can measure in this range). If in one side the reading is 10 megohms to 20 megohms, or at least approximately in this range, and the other side is infinity, we can say that diode is serviceable. The most common problem with high-voltage diodes is breakdown.
Checking the high voltage capacitor. Set the limit on the meter to 20 megohms and measure. A good capacitor should charge until it reaches a limit of about 10 megohms, that is, the resistance of the resistor in it. Except for the short circuit capacitor can also break, but it is better to check it by changing, simply put another capacitor.
Next, we test the transformer windings, first removing the terminals from the leads of the windings. The resistance of the primary winding should be about 2 to 4.5 ohms. The resistance, less than 2 ohms indicates that the transformer has an inter-turn short circuit in the primary winding. If the resistance is infinity, it means that the winding is open. Measure the secondary circuits. The resistance of the incandescent winding is 3 to 8 ohms, the resistance of the secondary winding is 140 to 350 ohms.
By the way, one of the signs of transformer failure, is a strong hum when you turn on the microwave.
Next in line is the magnetron, the source of the most frequent problems. The main malfunctions of a magnetron are:
- Breakdown of the cap of the antenna, which is a microwave emitter. This fault is easy to diagnose visually. This is often caused by a burned-out waveguide cover, which is a mica gasket. Mica conducts microwaves very well, but is also good at absorbing various fats, oils, etc.д. Then comes the moment when they accumulate so much that there is an electric arc and breakdown, because the electric field strength at the place of their greatest accumulation increases sharply.
- The next malfunction is depressurization, so the magnetron no longer generates microwave. The culprit here is usually corrosion of the copper, primarily due to overheating.
- Next is the failure of the magnetron filter feedthrough capacitors due to breakdown. This is because the supply voltage rises above the maximum allowable voltage for which the capacitor is designed. The capacitor breaks down on the housing and becomes short-circuited. To diagnose this problem you can use a multimeter. Touch the magnetron power supply pin with one probe and touch the other one to the chassis. If the multimeter shows infinity, then the capacitors are good. If there is any resistance, it means that one of the capacitors is broken or has a leakage.
- Tungsten filament breakage. This problem is also easy to diagnose. Use multimeter to measure the resistance of the magnetron pins. It has to be less than 1 ohm.
- Finally, another problem is related to loss of emission. The cathode area gets depleted during extended operation and loses the ability to radiate electrons into the work area, making the magnetron become less and less heated.
Basically, this is the whole diagnostics. The elements that are in the high voltage circuit are few and check will reveal the faulty. The only thing I want to remind you is to be careful when repairing the capacitor and do not forget about the capacitor’s discharge.