hi in the switching power supply age an electrical transformer looks like a three fingers marsupial but sometimes we have electronic equipment with bad transformers so we need to learn how to test them let's learn about it we have here an electrical transformer it has two windings it's just copper with some kind of a painting for insulation in several turns each one around I don't notice one of the winding is the primary and the other the secondary you would depend of how do we connect it on hold we need it in our case this is our primary winding and I have to connect it to 220 volts the secondary will give me 10 volts per each thread line in common with the black one in between that means I have a center tap transformer I have two windings in the secondary sometimes they are independent sometimes they are joined by the center so my diagram will look like this and here I will have ten volts AC and another temples AC Dunning's there is a ratio that I transform from one winding to the other in my case it is 22 to 1 every 22 volts I put here I will get one bolt in the output that's important to know now how do they work with the AC current and I wrote AC because we cannot transfer DC when the AC current comes to the primary it will make an induction magnetic field that will jump to the secondary we will see that with the oscilloscope in one moment what we have to do is look for the bigger adapter or transformer you have in your house or in your electronic worship and we will use it as the induction transformer I place my probe in the primary and the other one in the secondary now pay attention to the following graphics as I get closer to the adapter I get voltage in my transformer get closed loop this the screen that's the way to test such as former with the oscilloscope now as you see each graphic the new priest is they look alike Magneto timing voltage but what you cannot see on the screen is this knob is set to 10 volts ac per centimeter and the other knob he set it to half bald per centimeter 500 millivolts so in the real life this graphic is 20 times smaller than the other do you remember what I told you about the ratio okay that's the real graphics the secondary is 20 times smaller than the primary I will soon this one for them to look alike okay now I'm going to make a test I will take the older secondary and we'll make a short circuit I want you to pay attention to the red graphic what is going to happen with the voltage short it's a smaller the voltage is trooping why the voltage is dropping down is falling the voltage because I have a charged circuit so if I don't get pole - that means I have an open whining one of the reasons or I could have a charged circuit in one of them to remember with oscilloscope and even with a digital multimeter the voltage should increase as I get close to another transformer and the difference between the primary and secondary should be the ratio we calculate in the beginning and we are respecting to get now with a digital multimeter we are go we are going to use the volt meter and let's see what is going on in the primary once again I will get close to the transformer I get about eight hundred millivolts so twenty first twenty times less that will be about four hundred or less than four sorry forty or less than 40 millivolts is what we are expecting to get in the secondary the teeth a 40 millivolts is on the expectation with the radium so our transformer passes a induction test let's see now with the own mirror in the secondary we're expecting very low resistance because this transformer is a center tab I have two windings I will move the customer here I have to whine this so the other one should be like this but if I remove the center and I use the long way with both the point is I will get a little bit more resistance as I said if you get an open silk with Oh L overload that means the wire is broken inside in the primary we are expecting to get higher resistance than the secondary 141 ohms and the other was close to zero in the secondary this one the high one the higher one is the primary so now we know how to test them Thanks by watching it