Trial and error only cooktop unit. Everything mounted into the counter and needed to pull unit out. I figured it was a control switch or the burner itself. Based on costs, I took the less expensive route and replaced the 2 known malfunctioning switches. All on-line videos said it was a 2-3 hour process to replace. I finished mine in less than 30 minutes. Turned breaker back on and it works like a charm. 30 years old and still going strong.