How to test a microwave transformer

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Fred's Appliance Academy

Күн бұрын

Пікірлер: 90

@Gluluman 4 ай бұрын

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

@fredsapplianceacademy 4 ай бұрын

Happy to help Gluluman :)

@nikolaievans2432 3 ай бұрын

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

@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 10 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 10 ай бұрын

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

@vince6829 11 ай бұрын

Thanks for sharing your knowledge.

@DeborahVinti 10 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 10 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 10 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 2 ай бұрын

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

@fredsapplianceacademy 2 ай бұрын

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

@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!

@KAFKUBA 13 күн бұрын

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

@fredsapplianceacademy 12 күн бұрын

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

@KAFKUBA 12 күн бұрын

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

@fredsapplianceacademy 12 күн 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 12 күн бұрын

@fredsapplianceacademy thank you!

@Wayne-p7n 3 ай бұрын

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

@fredsapplianceacademy 3 ай бұрын

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

@southerner66 3 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 3 ай бұрын

Thanks southerner66 we appreciate the comment.

@LeruoSenau 25 күн бұрын

How do we check if the magnetron is working?

@fredsapplianceacademy 23 күн 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.

@jimmybonges451 4 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 4 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 4 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 4 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 4 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 4 ай бұрын

@@jimmybonges451 Thanks Jimmy we appreciate you.

@Rickzabor 8 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 8 ай бұрын

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

@mommawontstoporderingandit7105 8 ай бұрын

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

@fredsapplianceacademy 8 ай бұрын

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

@Wayne-p7n 3 ай бұрын

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

@fredsapplianceacademy 3 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.

@mvinayagar Жыл бұрын

Thank you

@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.

@glenmartin2437 Жыл бұрын

Thanks.

@MB-rt5bx 9 ай бұрын

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

@fredsapplianceacademy 9 ай бұрын

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

@mr5bassman 3 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 3 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.

@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!

@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 8 ай бұрын

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

@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 5 ай бұрын

@@ashchbkv6965maybe your multimeter is bad

@sidarior3814 3 ай бұрын

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

@fredsapplianceacademy 3 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 6 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 5 күн бұрын

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

@sidarior3814 5 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 👍

@ACommenterOnYouTube 10 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 10 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 10 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 10 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 ...

@aghilmousavi7450 3 ай бұрын

باسلام وسپاس عالی بود.OK

@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

@quintinplaza Ай бұрын

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

@fredsapplianceacademy 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.

@spencerdasilva Жыл бұрын

Everything shows 0 for mine.

@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 4 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 4 ай бұрын

Thanks again Dave!!!