Speedo Change

My Triumph Thunderbird 900 speedo dropped to around 30 mph while i was doing around 60 and then down to zero
I looked at the cable and it looked ok. But will have to get the front wheel off the ground to see if its spinning ( only have side stand). Normally when the cable goes the speedo just drops to zero. Very strange. I know by the revs roughly what im doing but i hate having something not working. If the Clock has buggered up its near £300 for a new or second hand one!! I found one for a Triumph Trophy 900 that look the same, Would it work?