If the trigger voltage is 2V, anything less than that will not cause the SCR to conduct. You must be careful how you measure it though, after being triggered, an SCR stays conducting until the voltage across it's anode and cathode drops below a certain level, probably around 1V or so. The trigger only has to be a very brief pulse and the chances are you wouldn't see it on a normal meter, an oscilloscope would be needed. I am not familiar with the machine but it does sound as though something is wrong with the SCR firing circuit rather than the SCR itself. The normal SCR failure symptom is they go short circuit rather than open circuit.
Brian.