The only real issue with the control board that could cause that is a failing relay or bad connection, both of which I can repair on a control board for $54.95, which includes insured return shipping.
The first thing I would do is test the outlet. A toaster or hair dryer are good devices to use.
A microwave must be on its own breaker, or at least not on the same breaker as a high-current device (stove) or a device that causes spikes on the line (fridge, freezer).
It's possible you have a failing magnetron or high-voltage transformer, but I would need to discuss it to narrow it down.
For free additional DIY help and details, feel free to e-mail me directly from my site. Remind me of your full model number and detailed symptoms.
William E. ("Ed") Miller
Microwave Oven Control Panel Repair Nationwide
"Recycling by repairing since 1982"