How to test a microwave transformer
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- čas přidán 3. 08. 2023
- 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.
www.fredsacademy.com
Clearest explanation I've come across so far!
That's what we like to hear! Thank you!
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!!!!!!!!
Thanks Tom. I do appreciate that very much.
From the guy in the video, Chad :)
Thanks for sharing your knowledge.
I have 5 wires coming out of the secondary winding. A thick pair, thinner pair, and a perhaps slightly thinner single. The smallest single goes to the caps. The thick pair to the magnetrons. The thinner pair goes to the other side of the caps, connected to the other side of the mags.
I think the single is a hv line. It's open to the thick pair, not to the casing, or the small pair, the later meaning it's junk. Sound right?
Thank you
Thanks.
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?
Most likely time for a new microwave if you're not willing to invest the $140. :)
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?
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.
@@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.
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 ?
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!
What does it mean if my secondary winding value is 142? Multimeter set at 200ohm
Secondary high its good. Secondary low there is a problem.
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
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.
Do we have to disconnect the transformer from the microwave to test? Because i cant get mine to disconnect from wires
Any time your ohm something out you should disconnect at least one wire to isolate the component being tested.
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.
When you have 240 and not 120 most things just double the resistance value. 4,800 is way too high for the secondary.
@@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.
My low voltage winding is showing nothing on the meter, not even moving from 0L. Everything else checks out, im assuming its bad?
Yep!
That's what I came to ask. Was getting no reading what so ever
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?
Hi there! At 156 ohms, it's likely ok. :)
@@fredsapplianceacademy u didn't add how to test a shorted transformer. My primary winding is shorted to the ground. Is it repairable?
@@safetyalways7788 we would not recommend attempting to repair. we'd recommend replaicng the transformer.
@@fredsapplianceacademy hi ! I mesured 230 ohms. Everything else is okay. Is it good ?
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
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?
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.
@@fredsapplianceacademy thank you so much for your reply
@@chrishadjipetris6059 sure thing!
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 .. ?
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.
@@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 ...
@@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 ...
My low voltage shows 00.0 ohms. Everything else checks out OK. Bad transformer? Thanks!
0.00 is less than 1, which is a good reading. There should be nothing wrong with it.
@@fredsapplianceacademyIsn't it a short circuit
@@Gamer-nv8bil am probably missing something here, because l also would expect something in the mproximity of 1ohm or even higher.
There's another type of resistance called impedance that limits the current 😉
@@Gamer-nv8bi Okay 👍
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.?
Any signs of burning and it should be replaced.
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.
Everything shows 0 for mine.