If he's an expert then it must be a bad board
However, only thorough diagnostic troubleshooting will reveal the actual problem. I've seen too many people throw money at a unit by replacing parts on a guess and still not get the problem solved. On top of the cost of parts they later had to pay a technician to troubleshoot & repair the unit when all else failed, thus just adding to the overall cost of the problem.
If you are able to check a few things on your own, you might just find the problem.
Can you do an amp draw reading on the blower motor and compare that with the specs on the motor's nameplate?
Are limit switches opening during the cycle and shutting down the unit?
How long after the unit shuts down does it take to fire back up?
Is there a thermostat controlling the fan cycle that is not kicking in soon enough?
What happens when you turn the T-stat to "Fan On" and have the T-stat call for heat?