Whirlpool micro wave oven model GM8155xjb-o. during long cooking time of bake potatoes ,fuse blew. replaced magnetron since it had a hole on the end .turned on microwave ...fuse blew again what would be the most likely solution?

please make this test and fix it. God bless you

1. Check the power diode This electronic component is responsible for transmitting current in one direction. If the diode becomes defective it will cause your microwave to not heat. Test the diode and replace it if necessary.
   
2. High voltage capacitor Responsible for storing electricity, this part is a key component in any microwave. Remove, discharge, and test the capacitor to determine if it requires replacement.
   
3. Damaged magnetron Responsible for generating waves and producing heat. When your microwave is no longer heating properly, replacement will be required.
   
4. Thermal Cutoffs Examine the thermal cutoffs on both the magnetron and the oven itself. Take off one of the leads and using a volt-ohm meter on RX1, check the terminals. If you get a result other than zero, replace the thermal cutoffs.
   

Put the potatos in a zip lock bag

Is the internal cooling fan working?

Are the ducts and vents clear?

Problems with any of those can result in overheating, which destroys magnetrons.

I have seen high voltage rectifier diodes interact with magnetron in funny ways. I'd replace the diode, too.

You can find links to helpful exploded view diagrams and part ordering help here.

I recommend that you bookmark that link to your favorites.

Finally, baking potatoes and making popcorn really give the magnetron a workout.

You should put about 1/2 cup of water in the rear corner of the microwave when cooking those foods.

It helps "preload" the oven to prevent execessive microwave energy reflection back to the magnetron.

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

There are three reasons for this, a bad magnetron "common problem" or a high voltage diode and capacitor can be a factor. If the magnetron is at fault it is cheaper to replace the microwave oven.

That was a very long duration to have set for potatoes. It would have made the magnetron burnt by exeeding the limit and findinf there was no conductive medium by moisture , it has ended up burning the magnetron.
First of all clean up the inside and clean up the point of the magnetron beam.Now confirm on the inside to be totally dry.
Disconnect power and check inside for break of fuse to the magnetron.If the microwave does not heat on testing with a cup of water , then it is possible that the magnetron is cooked.
Confirm the cost for the unit to decide on replacement.
Hope this helps.

magnetron is leaking internally, do not use until magnetron is replaced. the mag creates interference with the control board and resets it

The HV capacitor or Diode. In rare cases the mag could be shorted. This is a dangerous area to work in for the untrained. Eric

one of three things shorted could cause this: H.V. diode,capacitor,or the magnetron tube, take screw driver and short terminals on capacitor before touching anything inside the case, then chk resistance on capacitor should show infinite after needle settles, diode should show hi resistance one way and a lower resistance in the other direction(use the RX100 scale not the RX1) on both parts diode should not show very low resistance or it could be leaking,mag is a different story,it can be chk'd but in a different way

Did you use correct fuse??? REMEMBER MICROWAVES CAN KILL EVEN WHEN UNPLUGGED
grandadfixer

First you check the fuse at the out put of highvoltage of the transformer. If the fuse is ok, replace the magnetron.