Tech arrived at a service call. Upon arrival the customer mentioned that her son recently replaced the thermostat because the system was not working and that didn't fix it. The system was evaluated and the furnace control board has a tripped fuse. The fuse was replaced and the controll board sparked. There was visible heat damage. There was dust in the back of the board. The blower area and ductwork was dirty. The customer was informed of recommendations today. The tech advised repairs or replacement. The customer would like more time to contemplate her decision and will call back early next week. The tech will follow up next week if we haven't heard from her by then. The system was not functioning upon departure.