I am an electronics tech. My microwave stopped heating anyting but everything seems to work. Can you give me some advice on how to determinr if the the problem is the Magnatron, Transformer or the capacitor. I do gave a voltmeter.
The microwave in general can be divided in two parts: high voltage part and standard voltage part. The first thing you may want to determine is in which of these parts the problem is.
Remove the top grille and open the control panel. [diagram](http://www.gallawa.com/microtech/cap_test.html"]Discharge[/URL] the high voltage capacitor (#49 on the [URL="http://www.appliancepartspros.com/partsearch/model.aspx?model_id=216906&diagram_id=21658224)). Remove the wires from the high voltage transformer primary windings and check for 120 VAC between them while the control calls for heat and the door is closed. Post the results.
Here are the breakdown diagrams and http://www.appliancepartspros.com/partsearch/model.aspx?model_id=216906
Gene.
The 120 Volts is present.What is the nest step/s?
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The 120 Volts is present.What is the next step/s?
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. Can you sent three steps at once?
Thanks
Check the high voltage diode (#50 on the diagram) as described in one of our previous threads: http://forum.appliancepartspros.com/microwave-repair/19868-diode-testing.html
If there is nothing wrong, replace the magnetron (#73).
Gene.
Thanks Gene
So far I have discharged the capacitor (there were no sparks upon discaharge), checked the primary of the transformer with the secondary disconnected from the capacitor and magnatron and got 120 volts and have checked the diode. The diode #50 show open circuit on X10, X100 and extremely high resistance on X10,000 ohms scales. I always thought that a diode should have close to 0 resistance on foward current. Should I try the diode first or replace both magnatron and the diode at the same time?
The diode test you did required a very good meter. It is much easier and reliable to test it with a battery as described in the post linked in the previous reply.
Gene.
P.S. Did you remove the wires from the transformer primary before checking for 120 VAC between them?
Please click one of the Quick Reply icons in the posts above to activate Quick Reply.
— Begin quote from Gene;210445
Check the high voltage diode (#50 on the diagram) as described in one of our previous threads: http://forum.appliancepartspros.com/microwave-repair/19868-diode-testing.html
If there is nothing wrong, replace the magnetron (#73).
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The diode [part]AP3192533[/part]
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The magnetron [part]AP2025937[/part]
Gene.
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The diode testusing a 12 V battery shows 12.57 volts one way and 8.67 volts the other way. I removed the magnatron and looked at it. It doesn’t show any dark areas in the small hole on the top (tube). The limiter on the side of the magnatron shown short with wires disconnected. As far as I can determine (based on the forrum test proceedure) the cap. checks OK.
It sems to me that a clue is that the capacitor did not have a charge or give a pop when I shorted the terminals. Do you think the diode as well as the magnatron are bad and both should be replaced? I dont want to replace the mag. if it isn’t necessary.
Joe
Joe,
The diode is bad. No doubt about it. Very likely this is the only problem.
Gene.
Thanks gene. I ordered a diode today. I will let you know the outcome whe I get the part.
Joe
Hi Gene
I received the diode and the Magnatron yesterday. I replaced the diode first, powered up the microwave and attempted to heat a small amount of water. Smoke came out of the transfomer area. I then replaced the magnatron keeping the new doide. MORE SMOKE. Next I put the old diode back in an left the new magnatron in place. More smoke.
In each instance the capacitor did not have any charge.The new dioded (using the battery test now measures 8.57V one way and 12.56V the other.
I did not check it before installation. Could the capacitor be the problem? I mesured it as stated in previouse a message and it seemed to check OK.
I am baffeled!
Joe
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… Smoke came out of the transformer area…
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Joe,
This is very bad sign, especially if it did not smoke before.
Do you have the wiring diagram for the microwave? If you do, then double check all wires connections (the transformer to the capacitor and magnetron "F" & "FA" terminals and the diode) in accordance with the diagram. The new diode is now damaged.
Gene.
There are no wiring shorts. I think the diode was defective and caused the transformer to overheat thus destroying trhe transformer.This is the circuit I used to check wiring (http://www.gallawa.com/microtech/doubler.html). The capacitor has never had a charge.
At this point I don’t know if anything in the HV circuit is any good!
Joe
Joe,
I did not mean any wires shorted.
The transformer has two secondary windings - high voltage and filament (low voltage).
It is very important how they are connected to the capacitor and the magnetron. As you can see from the diagram (attached to the reply) the wire from the high voltage winding connected to one of the capacitors terminals while the one of the filament winding wire together with the diode and "FA" magnetron terminal are connected to the second capacitors terminal. The second filament filament winding wire should be connected to the "F" magnetron terminal.
The capacitor had no charge most likely because of a bad diode.
Gene.
The small secondary has about 0.4 ohms, The high voltage large secondary shows open from one side to ground and ashort from the other side to ground. All wires disconnected when taking resistance measurements.
Joe
Joe,
Looks like the high voltage winding is bad because its normal resistance reading should be about 70 Ohms. In the other word the transformer has gone bad.
Did you check the wires connections on the high voltage side of the microwave?
Gene.
All wires seem ok, That is no damage or opens. The only visable sign is the secondary part of the transformer (where the white lead connects. The tape holding the white lead to the Xformer is brown and has dislodged from the xformer. the area around the connection is dark brown as well.
Joe
Joe,
I did not mean wires conditions. I meant wires connections.
It proves a bad transformer.
Gene.
I am not sure where you are leading to. All connections are in good condition.All wire connections leading to the transformer check good. I hope thats what you meant. Thge fact remains that the transformer smoked after replacing the diode. The wires were replaced in the same order they were removed. there aren’t any wires connecting to any spot they aren’t suppose to.
The question to me is what took out the transformer. and what else in the HV circut is damaged.