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Good day,subject: LG microwave oven MS3448XRS not warming contents.Checked High voltage transformer 240 volt AC input-ok.Measure primary winding(0.2-0.4 ohm) measuring 1.1 ohm,secondary winding(70-100

Probably cheaper to buy a new microwave as they maintenance charge can be costly once put on a bench.
I am not able to help with this item.

Oct 01, 2014 | Microwave Ovens

2 Answers

Model "KOT-152UW" The

well inside the unit check for any burn fuses on the power supply area, and into the control board. fuse basically the one will tripped if power surged occurred..

Jun 27, 2008 | Microwave Ovens


How to check the High Voltage transformer in a microwave.

When your microwave is dead, you have checked the fuse and it is ok along with the power to the unit, and the control panel is dead, you probably have a bad transformer. It is the large device behind the control panel which has a laminated core. It will be hooked to the mains and supply power to various circuits.

Remove the power and the cover. Remove at least one wire from each side of the transformer. Check with a DMM for resistance. The primary, side hooked to the mains, should have continuity and low resistance, probably only several ohms. The secondary should have higer resistance but probably less than 100 ohms. If this checks out you need to see my tip at . Do not try to check the secondary under power as it will be at several thousand volts and is dangerous unless you are properly trained to do this!

If the transformer checks bad you can get a new one at a good price at


Thanks for using FixYa

on Mar 12, 2010 | Microwave Ovens

1 Answer

Just replaced the magnetron in my Panasonic NN-S543BFR. I still don't get any heat from my oven. Everything works as set but still no heat in oven. Need suggestions on repairs.

When you say "Everything works as set" do you mean the microwave appears to function properly, but then doesn't heat?

If the magnetron is new, then the magnetron must not be receiving the required high voltage (2000V or more) from the HV circuit. Make sure you've got 120V to the PRIMARY (don't attempt to measure secondary voltage of the HV transformer without special equipment) of the HV transformer. After that check the HV capacitor and diodes. If these components test OK, then either your HV transformer is bad or your new magnetron is faulty. My experience is that the problem is usually in control circuitry, preventing 120V to the HV transformer, or opens/shorts in the HV components (diodes and capacitors).

Mar 15, 2010 | Panasonic NN-S543BFW Microwave Oven

1 Answer

Kenmore Micro/Oven fuse keeps blowing

Disconnect the connector to the primary winding of the high voltage transformer. Put a new fuse . If the fuse is not blowing the problem may be in the secondary side of the high voltage transformer. Chek the highvoltage diode, capacitor, magnetron respectively. you can also check the primary winding of the low voltage transformer.

May 23, 2009 | Microwave Ovens

1 Answer

HV Transformer and Maganatron

I would not recommend an inexperienced measuring secondary voltage on the high voltage transformer! The filament winding produces about 3VAC but the high voltage winding produces well over 2000VAC! And that can be instantly lethal!

I would only recommend measuring the resistance (in ohms) of the windings with power off and capacitor discharged.

We have the full service manual for this model and have uploaded it to our site here to help you.

You will need the free Acrobat Reader to view or print it.

The part number listed by the distributor for the high voltage transformer is RTRN-A527WRE0 (zero on the end, not "oh") which is the same number shown in the service manual.

The two continuity checks on a magnetron are across the filament terminals, which should read about zero ohms, and from each terminal to the case, which should read open or infinity.

Even if a magnetron passes these continuity tests, it can still be bad.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

Oct 04, 2008 | Sharp R-930AK Convection/Microwave Oven

1 Answer

How to test high voltage transformer

#1 Turn off and un-plug the unit for 20 minutes

#2 There is as real risk of electrocuting yourself.

#3 Short the capacitor wit a screwdriver. BE READY for an arc or pop.

#4 You need a special high voltage probe to measure the high voltage. We're talking THOUSANDS of VOLTS here DANGER -DANGER - DANGER!

#4 If you want to try, you first have to DISCONNECT the capacitor from the circuit.

#5 DON'T re connect the power. Measure the resistance of the SECONDARY of the transformer (one lead goes to the capacitor). TELL ME WHAT THE MEASUREMENT IS..

#6 The rectifier could be bad (which is connected to the Capacitor) Usually - if one of th components is bad, it'll blow one of the internal fuses.

Mar 17, 2008 | GE JVM3670 Microwave Oven

1 Answer

Whirlpool MH6151XHT-1 - No Power - Stumped

First change all the fuse and check whether it works or not, if it does not work than as per your finding the secondary transformer could be the issue, the secondary transformer tap down the voltage fro 230-240/110 to required control board voltage. the best thing if the unit is opened then the right problem can be found but as per your description either fuses are faulty or the secondary transformer.

Dec 12, 2007 | Whirlpool MH1150XMQ Microwave Oven

2 Answers


There is something on the secondary side which is drawing too much current. I would check all electrolytic capacitors, zener diodes, transistors, and voltage regulators.

Mar 27, 2007 | Panasonic NN-C994S Convection/Microwave...

1 Answer

Samsung M1630 stepdown transformer details

That model doesn't show up at my normal Samsung US parts supplier. Can you post all the numbers found printed on the transformer? One of them should be the Samsung part number. Normally you can look at the voltage rating of the large filter capacitor on the control board and assume that the AC secondary voltage will be about 2V less (in ACrms) than that DC voltage. Now what I'm saying may seem a bit twisted - and it is - but what I mean is this: If the cap is rated at 15VDC, then I'm saying that a secondary voltage of about 13VAC rms should be a good safe level for testing. To confirm this, multiply 13VAC by .635 (assuming it uses a full-wave rectifier) and you get about 8.26VDC. Then allow for about 50% derating by mulitplying the 8.26VDC by 2. This gives you 16.5VDC, which with my generous derating, is pretty close to the caps 15VDC. Then you can remove the transformer and use an isolated Variac(tm) to apply that calculated AC voltage to the secondary connections at the circuit board to see if it powers up. You can measure the DC voltage across the cap as you adjust the Variac(tm), making sure you don't get too close to or exceed the DC rating of the cap. Once you get it working with a main DC voltage of about 50-75% of what's printed on the main electrolytic capacitor, you can start shopping for a sub transformer. It's much easier if it's not a VFD display which would require a separate filament winding, but there's nothing wrong with using a small second transformer for that. You can even mount them both on the chassis and run long leads to the board. As long as the leads are of sufficient gauge, routed and secured well, and protected from nicks, there's nothing worng with that technique. You should make them long enough that if the front panel is later removed for service, the next technician will be able to see the wires before he pulls them out or otherwise damages them. I would also add a varistor on the primary if there's not already one! *grin*

Sep 14, 2006 | Samsung MC1360WA Convection/Microwave Oven

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