Hello, the control board supplies 120 volts to a transformer and then the transformer steps it down to 24 volts. check to see if you are getting 24 volts at the transformer if not then turn off the furnace and check the Resistance of the transformer, you should read resistance if not the transformer is bad and must be replaced. If you are not getting 24 volts and the transformer checks out good then a problem could be the wires going from the board to the transformer or portion of the control board is bad.
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