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Within 3 seconds of turning on power to the unit, the primary side of the transformer burns out.

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You have direct short somewhere. I am a service manager and have been doing this 45 years. Take the low voltage side if the transformer and install 5 amp auto fuse. Two spades and wire . Its easy to do. This will protect the transformer. Your problem is a direct short or relay shorted. Disconnect wires at Air handler. Start with red and hook them up one at a time. I asume you do not have an ohm meter to ohm out the wires. Not a abd problem if you know how to approach it. Rusty

Posted on Jun 04, 2009


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Posted on Jan 02, 2017


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I install a new limit switch and now something keep burning out the transformer i replace it also and something keep burning it out what the problem could be

All transformer comes with a current limit specification in terms of VA units. For example a 24 v secondary coil with 6 VA specification only can hold a current of of 4 amps for a short period of time. So to prevent that it burned out you only pass an 80% of that current, then it really can hold 3.2 amps continuously.
Other possibles causes for burning the transformer are:
1. Accidentally connecting the primary and secondary reversed, the secondary can not manage the voltage and current of the primary .
2. A coil or device that is connected to the secondary is demanding to much current because is shorted or stuck in a position causing an increase on current.
3. The primary have multiple taps to operate on different voltages and the combination is wrong.
3. Faulty wiring. Some times the insulation of the wires became worm, cracked or melted, with the wires torches the metal a short is produced and the transformer burns. Check the wires carefully.

Hope these tips help,.

Jan 08, 2016 | Heating & Cooling


How to measure Voltage in Transforme for Fitness Treadmill

Transformer Test Procedure:1). Make sure that transformer wire connections (CON1) to the drive board are secured. Turn unit on.2). Put multimeter to the AC voltage setting. Insert meter probes into the transformer primary (red)wires as shown. Normal reading: 110V. This shows that there is power to the transformer.3). Test transformer output by probing on secondary (output) wires: black and black, white and white,orange and orange, yellow and yellow

Transformer Test Results :1). If there is no voltage across the primary (red) wires, inspect F1 fuse on the drive board and power to the drive board. 2). If there is voltage across primary wires but none across secondary wires, the transformer is bad.Replace it.

Transformer Wire Colors Normal Voltage Value:
Red and Red 110 VAC.
Black and Black 11-13 VAC
White and White 11-13 VAC
Orange and Orange 27-29 VAC
Yellow and Yellow 10-12 VAC

on Oct 26, 2011 | Exercise & Fitness

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Hello, I have a oil fired hot water heater, the motor comes on for about 30 seconds, and then stops running, I have oil and a flame, what do you think, thank you ,,,Greg

It sounds to me like it could be one of three things....

1. You have a poor quality flame. This could be caused by a dirty nozzle, or a lack or air. Ensure that the airband on the oil burner is not all plugged up with dust, lint, pet hair, etc..

2. You have a defective or dirty Cad Cell Eye/Assy. To check this you will need to turn the power to the water heater off. Loosen or remove the screws that hold the ignition transformer down to the burner. The transformer is hinged and should now swing open for you. With the transformer swung open you should see the cad cell assy. It is a round object most likely mounted on the transformer itself, in between the high voltage leads/contact. The eye itself will pull out of the assy. Use a clean cloth and wipe down the eye. Reseat into the socket and resecure the transformer. Turn power back on and test.

3. Bad Primary Control This would be the most costly of the problems, and would mean your control, located on the side of the burner needs to be replaced.

The final testing will require the use of an ohmmeter. Disconnect the two wires located on the side of the primary control, designated "FF".
These are most likely going to be yellow in color. Connect one wire to each side of the ohmmeter and turn the unit on. Your ohm reading will tell you the "strength" of the flame. The lower the number the better!
0-400 ohms is ideal; 400-800 is okay, anything above 1000 ohms means you need to replace the cad cell. Note: While perfoming this test place a jumper wire across the open "FF" teminals after the burner has fired up. (If done before the unit will not turn on). If the system shuts off on safety while perfoming your test (as long as you let it run over the 30 sec.) then you will know you have a bad primary control.

Hope this helps

Mar 02, 2012 | Heating & Cooling

1 Answer

There's no high voltage ,thus no magnetron activity

check the ceramic fuse in the primary circuitry as it probably blew out when the primary connection arced and burned through

Mar 23, 2010 | Magic Chef MCD1110ST Microwave Oven

2 Answers

No power to thermostat

You need a serviceman. No really, you do! You are in over your head and you are replacing parts just because you can see them and they are not the likely culprit. I am betting it is the contacters in your condensing unit.

Sep 01, 2009 | Heating & Cooling

1 Answer

Is not turning on

These sets opperate on what is called a switch mode power supply . that means that the power is electronicaly switched on inside the set after you push the remote or on button . A primary power circuit passes the current thrrough a series of rectifiers and transformers to control the smooth flow of electricty within the set , on the secondry side , the circuit alters the power again via transformers and circuit reducers to go to the different parts of the set the PSU is primarily a distributor .. the noise you can hear is probably the secondry side of the transformer oscilating due to a short or a component malfunction . the short can be in many places within the set especially within the High tension part of the circuit that generates up to 25,ooo volts in some cases per cathode ray tube and most Crt projection units have 3 Red Blue and Green that converge onto one spot to give the primary colours and the picture .
under each tube is the line output transformer this is responsible for generating the High tension it does this by means of an Oscillating transistor usually fitted to a large heat sink near the transformer if these go this will cause the type of fault you describe as the transformer trys to start a squeal is heard ( the tubes trying to charge ) and the set shuts down on most sets the sound circuit will be fed from one of these transformers and will fail at the same time and this is just one possible scenario .. I hope this helps you and must state that unqualified persons who remove the covers of live equipment are at risk of fatal electric shock .. and it is advised that no one without proper training should attempt this . Regards Vortash

May 04, 2009 | RCA HD52W59 HDTV Projection Television

1 Answer


what I have always been told is if your 24 volt side burns out check the high volt side if the hi volt side burns out check the low volt side.

A quick way if the primary side is burningout due to a problem with the low volt side:
1 MArk all the thermostat wires at the indoor unit
2 Disconnect them at the indoor unit.
3 Check main line voltage before proceeding (A 208 volt is not considered 220V and 240v Is not considered 208V> In these circumstances the voltage may have changed with the power company replacing a transformer and now you need to change the main power input lines at your control transformer for the correct operating voltage). If okj then proceed:

4 If you have an amp meter attach it to one of the lines going to the transformer.
5 Apply main power and listen for hum, note if smell starts again and if so problem has to be in board or main incoming voltage too high or too low. Amp draw should be less than 3 amps.
6 If your to this point and still havent found any trouble in the above as of yet, Connect the wire marked "C" together. Then just touch the thermostat wires one at a time to the places where they go on the indoor unit and watch the amp meter. If you donmt see the meter jump the circut is probably ok but leave them disconnected until you touch all of them to the correct place or wire. Here is a possible problem I ahve seen a thermostat wireing problem if the wires are stripped too far and a "whisker" of the wire sticks out and allowes one of the other wires to cross short out. In this case just cut off the excess wire or bend it over out of the way asnd continue with the test. You can always cut it off later after the tests. If you see the meter jump up and stay up and /or blowes the fuse the wire that you used and it blew is where to consentrate.
7 No wiring problem found means that you could have a relay or contactor not pulling in properly.
and this will cause the amp draw to go way over the transformers power out put or VA rating.
8 Inspect the thermostat wiring for the "whisker" I mentioned above.
9 If you have done this to the end of the thermostat wires and your main incomming voltage is correctly wired in on the transformer andf your relays and contactors are pulling in evenly and not delaying excessively your problem should be fixed.

If this helps you please rate me as high as you can and thank you for using fixya.

Apr 24, 2009 | Heating & Cooling

1 Answer

Power surges

Does it attempt to startup at all? Do you get any lights or any indication that the unit is trying to start? If not, there should be a small transformer inside that is the standby transformer. It generates the 5V standby voltage. I have seen these go open in the primary since there is a fuse built into the transformer. You may need to replace this transformer. You should be able to get to the primary winding. With the unit unplugged, measure across the primary side with an ohmmeter. You should read a low value. If it reads infinity, the primary is open and you need to replace the transformer.


Aug 07, 2008 | JVC RX-517V Receiver

1 Answer

Yamaha RX-V995 no power no audio [dead]

sounds like a short in the cpu of the unit

Mar 02, 2008 | Yamaha RX-V995 Receiver

1 Answer

No control power

PRIMARY means INPUT(from supply side)
SECONDARY means output( to load side)

Sep 23, 2007 | Maytag M6D24E7A Air Conditioner

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