If
it stops after 22 seconds, that means the controller has detected a
problem, usually a problem with the inverter or a bad magnetron.
Due to the lethal voltages used and produced, I do not recommend that an inexperienced person work on these.
You can
find an authorized Panasonic servicer here.
Shops generally charge about $75 for a home visit, then about $75-90 to do the repair work.
You can price Panasonic parts at
Tritronics, but if you don't find what you're looking for there, try
here. Shops might mark up parts from 25-100%, depending on the cost of the part.
If
nothing else, you can save about $75 by taking it to the shop yourself.
I'd say it would run about $200 or so if you take it to the shop.
We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.