HV Diode shorted twice! Transformer, capacitor and magnetron seem ok.

[ChrisAce81]

Model Number

MMV6178AAW

I have a Maytag convection/microwave combo (MMV6178AAW). I found a "shorted" diode (25 ohms both directions). I replaced the diode with a new one and it shorted again. I used a capacitive HV probe to measure the HV transformer output. I get 6.5kV pk-pk while disconnected from the rest of the circuit. Also tested the filament and it is about 3VAC. The capacitor also measures 1uF using a meter. All that is left in the circuit is the magnetron. Magnetron filament measures ok and no short to ground. Will a bad magnetron cause the diode to short? The magnetron either caused the original diode to short or the diode shorted on its own and then caused the magnetron to fail, which is now causing any new diodes to short immediately. Also, the old diode says RG508 but the replacement one says RG311. I am having a tough time looking up specs, but I presume that the 311 is a lower voltage rating, so maybe I just have the wrong replacement diode and that is the reason it failed again. Regardless, would you suspect a magnetron? Is it standard practice to replace a magnetron along with a new diode if the diode is found to be shorted as opposed to open? Any help is greatly appreciated! Thanks!

 

[jeff1]

Hi,

Will a bad magnetron cause the diode to short?

Yes it can...and visa-versa.

No pic Magnetron

Diode- black sleeve

Is it standard practice to replace a magnetron along with a new diode if the diode is found to be shorted as opposed to open?

Don't see many diodes open or shorted....but now when ever we have a bad mag we have been changing the diode at the same time.

jeff.

 

[ChrisAce81]

Thanks for the response. I was afraid of that. Unfortunately this unit's magnetron is $160. Not worth it in my opinion. To the junkyard...

 

[jeff1]

Time for a new unit.

jeff.