Testing a microwave magnatron

[Rob Davis]

Hi all.
Is there a good way to test if a magnetron is faulty. The microwave runs but nothing heats and almost no power is drawn from the ac.
The filament reads well below 1 ohm. There is no continuity between the filament winding and the case of the magnetron at all.
If I power the microwave transformer from my variac , I get about 1KV on the capacitor when I'm somewhere between 30-50VAC on the input , so I'm assuming the transformer , HV diode
and capacitor are ok. Transformer measures 1.65 ohms on the primary and about 130 ohms on the secondary. Filament winding measures almost short.
When 220VAC is applied to the transformer , the filament gets about 2.6-2.7VAC , which looks correct from the little I know.
Everything is pointing me to the magnetron , but I'd like to be able to know for certain before buying a new one.
Cheers
Rob

 

[_teliaz]

Hi all.
Is there a good way to test if a magnetron is faulty. The microwave runs but nothing heats and almost no power is drawn from the ac.
The filament reads well below 1 ohm. There is no continuity between the filament winding and the case of the magnetron at all.
If I power the microwave transformer from my variac , I get about 1KV on the capacitor when I'm somewhere between 30-50VAC on the input , so I'm assuming the transformer , HV diode
and capacitor are ok. Transformer measures 1.65 ohms on the primary and about 130 ohms on the secondary. Filament winding measures almost short.
When 220VAC is applied to the transformer , the filament gets about 2.6-2.7VAC , which looks correct from the little I know.
Everything is pointing me to the magnetron , but I'd like to be able to know for certain before buying a new one.
Cheers
Rob

Top-notch troubleshooting, Rob. You've methodically covered all the right bases and eliminated the other high-voltage components. You've hit on the frustrating truth of magnetrons. They can pass all the multimeter tests with flying colors and still be a dud under load. A final visual check for cracked magnets or a burnt antenna tip is a good last step, but I'd say you've already put your finger on the problem.

 

[Rob Davis]

Thanks , I guess I'll have to take out the magnetron and see if I can see anything. Going to have to replace it either way , not like you can fix it!
Not even that old , think the microwave is just out of warranty. Typical!

 

[Rob Davis]

Just an FYI , it was a cracked magnet :0(
Are magnetrons fairly generic?
If I find a magnetron of similar power and will physically fit( good seal on RF gasket) , is it likely to work?
Mine is a 2M248j , and I can easily get a 2M246. They are similar power levels +-1000W
Cheers
Rob

 

[_teliaz]

Just an FYI , it was a cracked magnet :0(
Are magnetrons fairly generic?
If I find a magnetron of similar power and will physically fit( good seal on RF gasket) , is it likely to work?
Mine is a 2M248j , and I can easily get a 2M246. They are similar power levels +-1000W
Cheers
Rob

Hi Rob! A cracked magnet is a definitive failure, so that's a great confirmation of the problem. Be cautious with replacements as they're not generic. You must match the mounting tab configuration and the airflow direction of the cooling fins. Does the datasheet or photos for the 2M246 show that its mounting and airflow match your original part?

 

[solo.shifter]

Ah, that explains it, magnetrons are a bit picky, power and physical fit matter most, plus the RF gasket seal. A 2M246 should work fine if it matches closely in power and fits well, but keep the mount and cooling requirements in mind

 

[Alan]

Hi all.
Is there a good way to test if a magnetron is faulty. The microwave runs but nothing heats and almost no power is drawn from the ac.
The filament reads well below 1 ohm. There is no continuity between the filament winding and the case of the magnetron at all.
If I power the microwave transformer from my variac , I get about 1KV on the capacitor when I'm somewhere between 30-50VAC on the input , so I'm assuming the transformer , HV diode
and capacitor are ok. Transformer measures 1.65 ohms on the primary and about 130 ohms on the secondary. Filament winding measures almost short.
When 220VAC is applied to the transformer , the filament gets about 2.6-2.7VAC , which looks correct from the little I know.
Everything is pointing me to the magnetron , but I'd like to be able to know for certain before buying a new one.
Cheers
Rob

Ah man, cracked magnet is rough, have you been able to get it sorted out?, would appreciate an update on how you went about it