Samsung SMH7187STD restarts after a couple of seconds

I have a 5 year old Samsung SMH7187STD over the range microwave. It begins every cooking operations fine, but shuts off (loss of all power) and restarts after a very short time. When using just time cook, just a couple of seconds, longer (about 15 seconds) when using the pre-programmed buttons. It started this problem a few months ago and has progressively become more frequent and now happens during every attempted use. Any ideas, my amateur investigation today indicates possibly the magnetron's thermal cutout?