How to test a microwave transformer

Рет қаралды 95,044

Күн бұрын

Please be sure that the microwave is unplugged before testing the transformer. You must also properly discharge the capacitor after the unit has been unplugged. Please reference our video on discharging the capacitor. So here's our microwave transformer, and this is responsible for driving the high voltage side of your microwave. And we have three different windings in here. We have our primary winding, which we can see down here is a little bit thicker gauge wire. It's kind of hard to see, but down in between the two large windings is our low voltage winding, and there's one wire here and an additional wire coming off the backside. And then the upper winding here, it's a little easier to see on this one. It's a much smaller wire. This is your high voltage winding, and this is going to be 2000 wraps of wire, which is going to give us about an equivalent of 2000 volts of output. And that comes out on this little wire here.
If you're familiar with power at all, you know that the power has to return to the source, and that is done through the actual body of the transformer itself. So voltage exits here. The neutral wire actually returns to the case of your transformer, and that's usually done through little tiny screw holes down here. So we're onto ohms. Let me see, ohms, OL. And then we're simply going to take our two leads. We're going to do the primary winding first. I'm going to put it on there and we should have five or less ohms. And here you can see we have 0.4, and that tells me that our primary winding is good.
Next, we're going to take our transformer and I'm just going to turn it to the side so we can see the wire coming off the back here as well as the wire in the front. And I'm going to go ahead and slip one meter lead right here, and then I'll take the additional and put it here. This is a much smaller winding and it should give us less than one Ohm always. If it's over one ohm, you would have something faulty inside of here. This transformer would need to get replaced.
So now we have the transformer facing us again, and we're going to test the high-voltage winding. We're going to put one meter lead there, and we're going to take the other meter lead and we're going to go down right inside that little screw hole there. And we should get between 35 to 150 ohms. And you can see right there we're at about 86.2. So that tells me that the high voltage winding on this transformer is working or should be working. I should mention that you also want to check for obvious signs of failure. If we have any burning or charring or discoloring of the wires or any part of the windings, this transformer has been compromised. It is going to need to get replaced. And that only goes for the front side, but for the backside as well. And this little wire right here, that's the return for the high voltage winding. So the output here and the return again goes to the chassis or body, whatever you want to call it.
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@uraclint 5 күн бұрын

Like so many others, I commend your 'no bullshit, no waffling and no self inflation" method of delivery. Thank you for that. subscribing.

@thesadboxman Жыл бұрын

Clearest explanation I've come across so far!

@fredsapplianceacademy Жыл бұрын

That's what we like to hear! Thank you!

@tomh.3513 11 ай бұрын

Clear,, to the point with no b.s chit chat simple as that but too many other utubers just don't get it. Thank you and thumb up for your video. Actually I have noticed other of your videos have the same format. Excellent work!!!!!!!!

@fredsapplianceacademy 11 ай бұрын

Thanks Tom. I do appreciate that very much. From the guy in the video, Chad :)

@Gluluman 5 ай бұрын

very short , clear and to the point ... which it was a simple to grasp for none technical people

@fredsapplianceacademy 5 ай бұрын

Happy to help Gluluman :)

@nikolaievans2432 4 ай бұрын

I'm pretty sure non technical people don't need to know how to use a high voltage transformer

@vince6829 Жыл бұрын

Thanks for sharing your knowledge.

@mattjenson1917 6 күн бұрын

What happens if you plug that into the wall with a spliced 120v cord?

@LeruoSenau Ай бұрын

How do we check if the magnetron is working?

@fredsapplianceacademy Ай бұрын

you cannot do any voltage checks on the mag itself, but if the trans, cap, and diode are checking good, then by process of elimination, you have a faulty mag, even if the ohm checks on it are good.

@mr5bassman 4 ай бұрын

From the white secondary to the body, I get 127 ohms, but feom the red secondary to the body there is nothing. This means the transformer is bad. Is that correct? My microwave stopped heating. The first thing I noticed when i took the shell off was the connector burned (its plastic charred) on the white primary wire.

@fredsapplianceacademy 4 ай бұрын

The only wire that should have ohms to the body is the secondary high voltage wire. Any burnt connection is never a good sign. I would walk through our other videos and test the remaining components.

@Wayne-p7n 4 ай бұрын

Not sure but do you have to test both secondary wires to body

@fredsapplianceacademy 4 ай бұрын

You can. You should have no resistance ( OL ) from the primary contacts to the body of the transformer.

@quintinplaza 2 ай бұрын

the high voltage side on mine shows 320 ohms,That is probbally very bad

@fredsapplianceacademy 2 ай бұрын

If its a over the range microwave I would say that's too high. If it's a counter top microwave it's still a little high but should work. Countertop transformers are usually smaller and have a higher resistance around 225-250 ohms.

@KAFKUBA Ай бұрын

I had 234ohms in secondary of my HV xfmr... what do you think

@fredsapplianceacademy Ай бұрын

Is this a countertop microwave or a over the range microwave? I also assume it is a 120vac unit.

@KAFKUBA Ай бұрын

@fredsapplianceacademy cheap counter top 120vac...grabbed it from work for parts

@fredsapplianceacademy Ай бұрын

@@KAFKUBA The resistance checks fine then. the countertops have higher resistance transformers on the high side. they are normally not repaired because parts are not available to do so.

@KAFKUBA Ай бұрын

@fredsapplianceacademy thank you!

@DeborahVinti 11 ай бұрын

Could I have your opinion.Great video BTW Thank You. My Over the stove microwave blows the breaker after 15 secs. On the transformer, Primary leads read 0.8 ohm, terminals to magnetron read 0.4 ohm however High voltage terminal to ground reads 194 ohm ( over the 150 stated in video) Is this the problem or is the transformer good?

@fredsapplianceacademy 11 ай бұрын

194 is a little high. If the winding shorts while it is running it can pop a breaker. This is not a common issue but it can happen. I would plug a kill a watt mater into the outlet and check the microwaves amp draw. It should be drawing around 12-15 amps. A breaker can withstand a continuous current draw of 60% if its rating. for example a 20 amp breaker can allow a continuous draw of 16 amps and not pop. If the amp draw is not to high then you have a problem with your electrical. If the amp draw is in fact to high I would also test the capacitor, diode and mag to be on the safe side with the diagnosis. Please watch our videos on how to do this.

@DeborahVinti 11 ай бұрын

@@fredsapplianceacademy I'd like you to know that your help and diagnosis was spot on. A Kill a watt meter proved you correct. Diode, capacitor and magnetron tested fine. Bought a new transformer and we are microwaving again. What a wonderful resource you are. I like your expertise and the way you answer peoples questions, real professionals. GOD Bless.

@MrDunk66 3 ай бұрын

Shouldn’t there be also be a check for windings shorting to the transformer body? Perhaps using an insulation tester [megger]?

@fredsapplianceacademy 3 ай бұрын

You can use the multimeter to test the windings to ground. Sorry if we missed that in the video.

@jimmybonges451 5 ай бұрын

Good day Mr. I would like to ask you regarding the microwave Transformer. I had taken out the transformer from the microwave unit and i was doing measurement at the primary, secondary and hv wire winding with digital and analog miulimeter, all are good, My question is: Why the transformer makes loud humming noise when I was connected the primary to 220volt ac, is this a symptom that the transformer is going damaged? Your reply very much appreciated thanks🤝

@fredsapplianceacademy 5 ай бұрын

In shorts as the AC current passes through the winding it creates a magnetic field at 60 hertz. The hertz is a frequency like sound waves and this vibration is what you hear. Here in the states the primary is designed for 120 vac so over driving it with 220 vac can make the hum louder. Hope that helps.

@jimmybonges451 5 ай бұрын

Good day Mr. The transformer is designed fr 220vac it’s not 110vac..you right as normally when we test the transformer(just live testing without any secondary connected to) there will be any vibration and a little hum.. but in this transformer is abnormally sounds come out. Anyway . At the end i replaced the transformer with the new one ..and now the microwave running normally. I suspected there is a loose wire roll of transformer winding inside due to their age .. the microwave product is year 1993.. Many thanks appreciated for your reply.

@fredsapplianceacademy 5 ай бұрын

@@jimmybonges451 1993 That's so awesome!!!!!! Good for you and keeping things alive. Another thing that can cause excessive noise in the transformer is the metal plates that are welded together start to separate. Either from small cracks in the plates or the welds. when the primary gets energized the magnetic field wants to push them apart and then they vibrate abnormally. Thanks for getting back to us Jimmy. we are very happy to be of any assistance.

@jimmybonges451 5 ай бұрын

Yes you right.. agreed🤝it could be from the metal plates .. the beginning of the problem this microwave oven was the main fuse alwys blown off when turn it on. All the critical components the critical components such as HV capasitor, HV diode, and the Magnetron all checked are very good, that’s why I was doing live testing the transformer just injected the primary side to 220Vac then straight away abnormally a very loud buzzing sound was heard. After replaced the transformer with the new one the problem went away. So, Many thanks and much appreciated to your goodness🤝🙏🏻

@fredsapplianceacademy 5 ай бұрын

@@jimmybonges451 Thanks Jimmy we appreciate you.

@southerner66 4 ай бұрын

Good explanations for checking DC resistance of windings, but I have seen cases in transformers where an inter-winding short would only appear with the kind of high AC voltage swings seen in actual operation. A DMM will not reveal these.

@fredsapplianceacademy 4 ай бұрын

Thanks southerner66 we appreciate the comment.

@denzilharris7509 Жыл бұрын

Need a little assistance. Got 0.5 ohms on the low voltage from pin to pin Got 0.5 ohms from the two low voltage wires. I only have one wire coming out of the high voltage side. How would I check that side exactly. Checking from the high volt to the low volt wire the meter reads OL

@fredsapplianceacademy Жыл бұрын

You muST check the high voltage wire (the single wire) from it to the steel body of the transformer where a screw has gone in and anchored it. The steel body is covered in a lacquer to prevent shorting so that is why you must test on a screw hole or something that is bare metal and not coated.

@Wayne-p7n 4 ай бұрын

So 8 ohms across primary is no good and would that cause blowing a fuse every time you hit start?

@fredsapplianceacademy 4 ай бұрын

8 is a little high but I don't think it should blow a fuse right after hitting start. I would be looking for something with an abnormally low resistance, shorted cap or diode even.

@mommawontstoporderingandit7105 9 ай бұрын

Do we have to disconnect the transformer from the microwave to test? Because i cant get mine to disconnect from wires

@fredsapplianceacademy 9 ай бұрын

Any time your ohm something out you should disconnect at least one wire to isolate the component being tested.

@Rickzabor 9 ай бұрын

Great video. Will subscribe. I have a GE microwave that has components looking like what you show in the video. All of the transformer reading were within your ranges but 2 wires that were attached to the low voltage side of the transformer burnt off at the connector. I don't see any evidence of windings being charred. Should the microwave transformer still be replaced? the microwave is 10 years old and I"ve already replaced or fixed 2 door switches. Transformers are about $140 and a new microwave about $500. Is it time for a new microwave?

@fredsapplianceacademy 9 ай бұрын

Most likely time for a new microwave if you're not willing to invest the $140. :)

@ACommenterOnYouTube 11 ай бұрын

So my microwave blows the 20A fuse IMMEDIATELY after hitting start. Opened it up, found the blown fuse, replaced it, thinking we are good, set the time, hit start and the fuse blows instantly again. I found the schematics inside with troubleshooting instructions, it tells me the HVT is grounded. So i checked for a ground fault on that leg that goes back to the 20A fuse but NO ground on it, its clean. I checked the HV side and got .2 ohms across the 2 wires. I checked the wire that goes back to that fuse for a ground on it, nothing, its clean. So how is this a faulty HVT when all readings show good and no ground faults on the transformer itself NOR the 120V feed wire .. ?

@adambutcher4204 11 ай бұрын

The transformer is ground to the microwave through the body of the transformer where the screws secure it to the microwave. You need to check the windings to the body of the transformer. There should be no resistance from any of the windings to ground.

@ACommenterOnYouTube 11 ай бұрын

@@adambutcher4204 i did , its infinite ohms on all leads to the chassis so its not grounded, however i did check the capacitor that its wired to and it has a 1.2 ohm short across it ...

@ACommenterOnYouTube 11 ай бұрын

@@adambutcher4204 So i swapped out the High Voltage Cap and this one acted like a normal cap, short then charged and went to infinite resistance. Slapped it in and now the microwave works perfect. Funny how the troubleshooting schematic said it was the Transformer but it wasn't ...

@ashchbkv6965 11 ай бұрын

Where I'm from the input voltage is 240v, does this change anything? the primary reads 4.7 ohms and the secondary reads 4,800 ohms (yes, 4.8k), is it too high on the secondary side? I've tested multiple times and made sure the probe touches the scratched surface of the body, the readings are consistent.

@fredsapplianceacademy 11 ай бұрын

When you have 240 and not 120 most things just double the resistance value. 4,800 is way too high for the secondary.

@ashchbkv6965 11 ай бұрын

@@fredsapplianceacademy So I just tested one from another microwave that's working fine, the resistance is lower but it's still 3.6k ohms😵 why are mine so high, it's so confusing.

@arifryo6823 6 ай бұрын

@@ashchbkv6965maybe your multimeter is bad

@chrishadjipetris6059 Жыл бұрын

So you're saying that the one terminal of the secondary winding touches the core of the transformer, which is attached to the metal case of the microwave. Isn't it dangerous, especially in case the ground wire is disconnected for any reason?

@fredsapplianceacademy Жыл бұрын

So you're saying that the one terminal of the secondary winding touches the core of the transformer, which is attached to the metal case of the microwave. Yes. Isn't it dangerous, especially in case the ground wire is disconnected for any reason? No. The entire metal cabinet of the microwave serves as the path of least resistance for the transformer circuit to be completed. As power must return back to its source (the transformer being the source) disconnecting any ground wire will not effect this circuit.

@chrishadjipetris6059 Жыл бұрын

@@fredsapplianceacademy thank you so much for your reply

@fredsapplianceacademy Жыл бұрын

@@chrishadjipetris6059 sure thing!

@MB-rt5bx 10 ай бұрын

What does it mean if my secondary winding value is 142? Multimeter set at 200ohm

@fredsapplianceacademy 10 ай бұрын

Secondary high its good. Secondary low there is a problem.

@hawser27 Жыл бұрын

My low voltage winding is showing nothing on the meter, not even moving from 0L. Everything else checks out, im assuming its bad?

@fredsapplianceacademy Жыл бұрын

Yep!

@mommawontstoporderingandit7105 9 ай бұрын

That's what I came to ask. Was getting no reading what so ever

@gouinjean-michel3911 Жыл бұрын

I open a used microwave for the transformer and the unit has a separate kind of way to make high voltage the primary seem to be separated from the secondary with out any case or frame but electronic card. What can you tell me about that, can the system can be use for a high voltage output ?

@fredsapplianceacademy Жыл бұрын

Hello! Only a factory issued part should ever be used or it could be extremely dangerous. If you're not sure how to service a Microwave safely, we recommend calling a factory authorized technician to assist. You may contact the manufacturer of your product directly to obtain a referral. Stay safe!

@glenmartin2437 Жыл бұрын

Thanks.

@sidarior3814 4 ай бұрын

Hello my microwave is working when the door open but when it closed it won’t work . What is the problem

@fredsapplianceacademy 4 ай бұрын

Hello Sidarior. You likely have faulty door switches. There are 3 in total. Replace them all at the same time and you should be good to go.

@AmosMantyla 29 күн бұрын

Has anyone messed with the connections? Those switches almost always have a N.O. terminal and a N.C. for "normally open" and "normally closed". Verify appropriate connections.

@sidarior3814 29 күн бұрын

@@fredsapplianceacademy I think I changed all 3 and it worked

@sidarior3814 29 күн бұрын

@@AmosMantyla sir you’re right just I forgot to answer Fred appliance

@TheTowkay Жыл бұрын

My low voltage shows 00.0 ohms. Everything else checks out OK. Bad transformer? Thanks!

@fredsapplianceacademy Жыл бұрын

0.00 is less than 1, which is a good reading. There should be nothing wrong with it.

@Gamer-nv8bi Жыл бұрын

@@fredsapplianceacademyIsn't it a short circuit

@pilatedndlovu8980 Жыл бұрын

@@Gamer-nv8bil am probably missing something here, because l also would expect something in the mproximity of 1ohm or even higher.

@Gamer-nv8bi Жыл бұрын

There's another type of resistance called impedance that limits the current 😉

@pilatedndlovu8980 Жыл бұрын

@@Gamer-nv8bi Okay 👍

@mvinayagar Жыл бұрын

Thank you

@safetyalways7788 Жыл бұрын

While other results are within ranges you mentioned, however, my high voltage wounding reads 156 ohms...can you pls interpreat this value because it exceeds 150 ohms range you mentioned?

@fredsapplianceacademy Жыл бұрын

Hi there! At 156 ohms, it's likely ok. :)

@safetyalways7788 Жыл бұрын

@@fredsapplianceacademy u didn't add how to test a shorted transformer. My primary winding is shorted to the ground. Is it repairable?

@fredsapplianceacademy Жыл бұрын

@@safetyalways7788 we would not recommend attempting to repair. we'd recommend replaicng the transformer.

@aprozsolt8046 Жыл бұрын

@@fredsapplianceacademy hi ! I mesured 230 ohms. Everything else is okay. Is it good ?

@fredsapplianceacademy Жыл бұрын

If it's a counter top microwave you should be fine. For a over the range microwave its a little on the high side. @@aprozsolt8046

@spencerdasilva Жыл бұрын

Everything shows 0 for mine.

@aghilmousavi7450 4 ай бұрын

باسلام وسپاس عالی بود.OK

@piecetoyou8285 Жыл бұрын

Some what I get it . On my high voltage wire from the secondary winding i am getting 22.4 ohms this is from a microwave oven Samsung 1929 model 1850w it has 2 transformers, is this to low. there are signs of burning and it smells but no smoke when i put the microwave on I get a little confused when you say the high voltage wire ,the voltage returns back and the neutral that is at the back connects to the body,,witch makes the casing have voltage running on to it, So the high voltage wire usually has a high amp fuse connected as well. So are you saying the voltage runs through the capacitor then out into the transformer then back out back to the capacitor ? And the neutral IS coming out from the secondary winding and connected to the back casing on the transformer has voltage travel through the casing of the transformer ` then goes down to the plate of the transformer and then where does it go? The screws on the plate that hold the transformer to the bottom of the microwave do they take the access voltage away I don`t under stand where the voltage that comes from the neutral that`s connected to the transformer body` how we don`t get shocked when touching the outer of the shell on the microwave casing I know that the transformer is coated on the out side with a varnish or shellac , So if it is coated does this keep the voltage trapped between the coating and casing of the transformer,or not, Could you please explain where this voltage goes from the secondary winding neutral wire that connected to the transformers body.?

@fredsapplianceacademy Жыл бұрын

Any signs of burning and it should be replaced.

@pilatedndlovu8980 Жыл бұрын

From the secondary out put through the high power fuse it goes into the cap and charges it.By the way the transformer,the cap and the magnetron are connected in series.So in this direction current reaches the magnetron as negative,(which is not effective to it. Because it is alternating current, flowing the opposite direction, this time the cap discharges into the transformer and the 2 voltage add up to double and goes into the magnetron as positive and the diode makes sure that it doesn't enter the cap except through the magnetron only.The same pattern happens 50 time every second this side 60 for you guys.

@davidfalconer8913 5 ай бұрын

Should ( anyone ? ) wish to check the EHT diode ( connected to the 1μF capacitor ) ... you CANNOT test this with a multimeter set to ( diode test ) , because there are several diodes in series , inside ... so .... to test , wire up with a 1 K Ω resistor in series and place the whole lot across a 30 Volt DC power supply , and you should read 8 to 10 Volts across the diode ( much like a Zener diode ) ... but ... in reverse , a Zener would read 0.7 Volts , and this diode should read the FULL voltage of your power supply , to show that it might hold off the full EHT ( ? ) .. ( tried - n - tested ) .. DAVE™🛑

@fredsapplianceacademy 5 ай бұрын

Thanks again Dave!!!