Where do i connect a "C" wire into my circuit board ? Goodman gmt140-5
Connect your C wire to the junction of the the fat light blue-grey wire and the thin white wire

While it does not look that your furnace has a control board, we can use another heuristic to identify the C wire in your furnace's connections.  Since it appears you have central air conditioning, we know that the thermostat is connecting the red and yellow wires in its cable to turn the cooling system on; from the furnace, as we can see, the yellow wire continues on to the compressor contactor as the red wire in the outdoor unit's control cable.

That 24VAC, then, has to return to the furnace's control transformer somehow, and it does so via the white wire in the outdoor unit's control cable.  Hence, that wire must connect to C in order for your air conditioner to work, and we can thus make our C wire connection at the point where it joins with the furnace's control harness.  Hence, just add your C wire to the nut where the fat light blue-grey wire from the furnace joins with the thin white wire from the air conditioner.