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Repair guides and troubleshooting information for microwave ovens.

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Samsung microwave ME19R7041FS

It powers on. When try to make a cooking cycle and push start the clock counts down, the lights come on and you hear buzzing as if it was heating. But, you won't hear the fan running, turntable not spinning and the food will not be hot.

Checked the door interlock switches (top and bottom ones are normally open, middle one is normally closed) with a voltimeter for continuity and they all checked out good when the door is closed and when it is opened.

The original turntable motor (21V) was removed for inspection and discovered burn marks on it and had no continuity. Bought a replacement but still not working.

I couldn't locate the circuit schematics but I read that the magnetron cooling fan motor acts as secondary transformer to reduce the voltage going to the turntable moror.

Is there any common connection to not heating, fan not working and fried the turntable motor?

Please, advise.

Thank you

Update (02/21/24)

The photos of the fan motor back and front (note the damaged winding)

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Hi @mosaabsilik,

The common factor may be the control board. (example only)

Perhaps also check for continuity between the primary door interlock and one side of the fan, the HV transformer and the door monitor interlock as the primary interlock switch is used to extend the Neutral (AC return path) whilst relays on the control board connect the AC Active. The control board AC power supply is before the door interlock switch so that the control board still works but the microwave HV circuit etc won't when the door is opened - safety feature.

Without a schematic it may be difficult but with most microwaves there are relays on the control board which are operated to supply power to the different components e.g. a fan relay, a turntable relay a power relay (which connects power to the HV components transformer, diode, capacitor, magnetron), interior light etc.

Looking at an image of the board linked above there are multiple relays seen

Normally the relays operate on an LV power supply circuit (transformer on the board) so since the clock counts down this indicates that there's LV power on the board (runs the display and clock) but this doesn't mean that the appropriate relays will be operated.

They should operate when the start button is pressed (as the clock has started to count down) so maybe the first thing to check is if there is power to the fan when the oven is started or at least prove the connection between the relay and the fan.

The 120V AC power rail is normally commoned over the relay contacts so when a relay is operated power is extended via the operated relay contact to the component.

This is all assuming that in general it is wired as most microwaves are.

As stated earlier, not easy without a schematic.

Be safety aware when working in microwave ovens. The HV capacitor can store >5000V DC for months even if the power has been disconnected from it for this length of time. This amount of voltage can seriously injure you. The HV capacitor needs ot be correctly discharged as soon as it can be accessed after the oven's cover has been removed and before any further work is done in the oven

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Hi jayeff,

Thank you for detailed and informative reply.

Would I still hear buzzing when the connection from the board to the transformer is bad?

My first task is to find the schematics. I have read they are supposed to be inserted within the control board but I couldn't find them. Perhaps they are inside the compartment where the HV components are (I am wary of the capacitor and I didn't take the microwave down and remove the cover to access back there. I am only trying with the front compartments where the board and connections are so far).

I will update you when I find the schematics.

Till then have a great day.

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@mosaabsilik

A relay could be making the buzzing sound or the fan or turntable motor trying to start but not succeeding so it's difficult to know.

Hopefully you will find the schematics

here's a link that may help with testing the HV components but I personally don't think that they're the problem. To me the oven has a break somewhere in the power supply for the components that use AC voltage which is everything except the control board although it does switch the AC to the components.

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Thank you for the link and thank you again for the advice.

I have found the schematics at the following link https://apps.fcc.gov/oetcf/eas/reports/V...

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@mosaabsilik

Well that makes it easier.

You can use an Ohmmeter to check the path from the Active pin on the power cord through the primary door interlock switch operated i.e. door closed, through to the fan motor and turn table motor to their respective relay contacts on the control board.

The other side of the relay contacts (which wouldn't be operated whilst your testing) would go to the Neutral pin on the power cord.

You just have to find if Active and Neutral get to the relay contacts.

If they do then it may be that the relay isn't operating which would make it a control board problem, probably requiring a new board as rarely if ever do they have schematics of the boards showing how the relays operate but nowadays it's a programmed in a chip on the board

I had it reversed in that I had the Active on the control board and Neutral through the interlock whereas it is the Neutral on the control board and Active on the interlock but in essence it is the same as it is AC current

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Hi jayeff,

I am sorry that I didn't get back to you sooner.

I just finished working on the microwave a couple of hours ago. Now it is working normally.

I found the root cause of the issues is all the magnetron fan motor. I wish I could send pictures here, but basically the wire windings around the motor look melted from the back side. And since the motor controls the turntable motor, and the magnetron fan is responsible for cooling the magnetron as well as circulating air in the cooking compartment by turning the stirrer fan (doesn't have a motor), the microwave had the problems listed in my original post.

Now, I am not sure what caused that damage to the motor. I checked all relays, thermostats, fuses and connections, nothing seemed out of order.

I would like to thank you again for your expertise and support.

I will post updates if there are any developments.

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