If the microwave buttons do not work it indicates that the touch-pad … After taken the capacitor out the chassis, another definitive test revealed a resistance of 23.7 Ω between the casing and one of the terminals. Anyhow, the remaining measurements that follows are all coherent. Thanks for this article that is written in a very fluent English and technical words . The Procedure for Testing the Diode, or Rectifier, of Your Magnetron: Get a nine-volt battery and insert the readers of your voltmeter as a standard. I´ve performed the implementation of these two methods as illustrated in the sequence. You are welcome, Beh. BE SURE TO UNPLUG MICROWAVE AND DISCHARGE CAPACITOR BEFORE WORKING ON ANY ELECTRICAL COMPONENT. I had already repaired it twice – one for magnetron replacement and the second for HV diode replacement. How to Replace Your Samsung Icemaker When It’s Not Making Ice, How to Replace Your Refrigerator Gasket Seal. When I applied the probes of the ohms tester between the chassis and one of the capacitor terminals (those connected directly to the magnetron), the short-circuit became evident. An ohmic resistance test was done in each winding, resulting OK. The measuring instrument would have to do some kind of special processing, and this not happens. The capacitor is in the back side lower corner. In one half-cycle, when the diode is forward polarized, the capacitor charges at a voltage 2 kV * 1,41 (square root of 2) ≈ 2,8 kV, tending to maintain this charged value constant. Anyhow, it´s a reasonable evidence of the transformer condition, that showed to be good in this case. An appropriate measuring would be with an oscilloscope on the tap. But that’s not really true. Nevertheless, this second method leads to some safety issues (See the important warnings at the end of this article). With its operating simplicity and speed of performance, it is an essential part of the modern kitchen. If you’re still hearing any sort of non-typical microwave noise, that’s a sign of a defective power diode, magnetron, or high-voltage capacitor (those are all real things! })(); The line marked as Diode On (not in scale ) in the above drawing corresponds to the voltage developed in the HV diode in the forward polarization, a very very small voltage, as compared to the 5.6 kV magnitude, is applied to the magnetron. Many thanks, Yogesh. Microwave High Voltage transformer:  Transformers are very similar but we recommend you pull the wiring schematic to locate what wire does what. In this helpful article, you will find out: what a motor capacitor does, the two main types of motor capacitors, and how to tell if your motor capacitor is bad. Loud noises such as bangs, buzzes, rattles and knocking while the microwave is in operation could indicate several things. Microwave buttons do not work. Be sure to discharge the capacitor before messing with anything inside the microwave. I learned a lot from it and I appreciate the time and detail you and others document your repairs and diagnostics. 239-574-4499. document.getElementById("af-header-413914580").className = "af-header af-quirksMode"; A transformer with 127 Vac at primary side and 2 kVac at the secondary has a 1:15.7 turns ratio (in the case of 220 Vac at primary side, this turns ratio is 1:9). In that case it was a short between the two capacitor terminals. For the following explanation let´s assume that the secondary voltage is 2 kVac. One of the output terminals plus the center tape were used to supply the primary of the microwave oven HV transformer. Really thanks for your Great article due to excellent explanation . Thanks, Tony. Use our step-by-step microwave repair guide to learn how to test your diode. Capacitors react to energy surges in various ways. My articles are not frequent (only three up to the moment), as I don´t deal with maintenance regularly. The secondary winding delivers a voltage around 2 kVac. During operation the tube become too warm and, besides the heat sink existing in the magnetron itself, the housing – and hence the anode –  is directly (mechanically and electrically) connected to the mass of the equipment which optimizes heat dissipation, simplifies installation and avoid the use of additional heat sinks. This “complex designed” voltage divider takes into account three premises: 1) The measurement at the voltage divider tap corresponds to 10% of the total voltage applied to the high side of the divider. In my case, since the microwave oven has stopped working and unplugged power for a long time and there is one discharge resistor in the circuit, so I didn't show the discharge steps. Nice article, Henrique. In fact, it is dangerous to work with high voltage, but when you are well informed and use the correct techniques, then the work can be performed safely. Faulty Door Switch. There are two things to consider about this method: the value is measured without load and the low-power step-down transformer employed makes it practically impossible to put any load at the secondary. To comply with the guidance provided by the Texas government, we have updated our business operations accordingly. if (navigator.userAgent.indexOf('FBIOS') !== -1 || navigator.userAgent.indexOf('Twitter for iPhone') !== -1) { I didn´t get to understand the reason why this occurs. Place your meter leads on the ends of the cap and you should see a quick rise and fall on your meter. That way, you’ll never miss a post. 958 Country Club Blvd. } As the transformer turns ratio is constant, the voltage developed at the secondary side is reduced correspondingly, allowing the measurement to be done safely and within the normal range of regular multimeters; b) Applying the rated mains voltage (127 Vac in my case) at the primary side and measuring on the secondary side through a resistive voltage divider, which also reduces the voltage to the range of usual measuring instruments. In this way the the upper wave peak (+2.8kV) is shifted down to 0V, and the lower wave peak (-2.8kV) to -5.6kV, but the waveform remain the same! -->. This article explains the various causes of premature failure of power factor capacitors and presents some best practices to extend the useful life of AC Power Factor Capacitors. The magnetron tube was disconnected from the circuit by drawing the filament Faston connector out. Oh! I would love to practice it more, but my other activities (I am translator of technical manuals and, mainly, a grandfather) take me a lot of time. if (document.getElementById("af-footer-413914580")) { if (document.compatMode && document.compatMode == 'BackCompat') { If I had one, a photo from the screen would be included in this article for better assessment. var IE = /*@cc_on! The test on the capacitor was repeated and showed that at least as one capacitor it was still good, with the multimeter needle showing the charging and returning to the rest point. When capacitors are in use, energy surges and high temperatures cause different kinds of failure. Isolate the high voltage circuit by removing one lead off the power supply leading to the transformer. Diode failure is often accompanied by visible signs of a burn out. The isolation values between winding were also measured, resulting OK too. Because of this, the measurement is done in a condition near the open state of the output, which tends to increase the value of the voltage being measured, mainly on the DC measurements, as will be seen further on. Problem is in HV circuit. (function() { Other aspects to note are: only one diode and only one capacitor are used; and the use of a voltage doubler means that the secondary of the transformer needs only half of turns. Thanks for sharing. When examining a failed electronic device, the failed capacitors can easily be recognized by clearly visible symptoms that include the following: Bulging of the vent on top of the capacitor.