Do not use alcohol it is FLAMABLE. Ultrasonic cleaning and heat will produce alcohol vapors that can flash. Use Branson EC diluted and rise with 90%+ (non rubbing) alcohol. Dry boards in small oven at 200F for an hour or so. Use sweeping ultrasonic cleaner to minimize chances of ultrasonic damage. Remember you get what you pay for in equipment. Used quality is better than new junk.