The BDR has a classic separate reverb tank; first thing to check is if the to/fro lead is properly connected into the amp. Check out the black 'twin' wire to the right in the picture, should be similar to yours.
I am not sure how this connects to tank or main chassis, but there should be a jack of sorts on one side or the other. Most likely, this has come loose during transport. There's half a dozen other ways to not have reverb while the rest of the amp works, but not nearly as likely as a loose connection - all other connections are on the board to opamp U2.
Edit: the two wires coming through the rightmost hole in the back face of the chassis, to the right of the speaker, in between the three flatcables, would be the prime suspects to me.
