Nando,
A thermostat's basic function is to regulate the operation of heating and equipment in your home. You set the thermostat to the desired temperature and the thermostat turns the equipment on and off to maintain that temperature. A thermostat is essentially an automatic switch. The thermostat senses the temperature and turns the air conditioner or heater on and off as required to maintain the desired temperature.
There are two basic types of thermostats: electromechanical and electronic. They both do the same thing but they do it in different ways. Additionally, of the two basic types, there are several varieties from which to choose.
An electromechanical thermostat typically uses a bi-metal coil or strip which moves as it expands and contracts with temperature changes. Mounted on the bi-metal strip is a glass vial partially filled with mercury. As the vial is tilted on the back on the bi-metal strip, the mercury flows to the end of the vial where two electrical contacts are exposed. When the mercury envelopes those electrical contacts, a low voltage circuit is made, thanks to the fact that mercury is conductive. This works just like a light switch and makes a circuit to turn on the heater or A/C.
An electronic thermostat operates in much the same way as an electromechanical model except that instead of the moving bi-metal strip and mercury switch, it uses a sensor to detect temperature levels. When the temperature differs from the preselected temperature the thermostat electronically makes the circuit to the heater or A/C.
Also, here is a link to an online circuit board repair center. As I understand it, you just send in your circuit board and they will test and repair it, and then send it back to you. They have a pretty good turn around time.
http://www.acsindustrial.com/printed...ard-repair.php
Let us know if any of this helps.