"Neil" wrote
....

An earlier message suggested the MJF122 darlington so I popped this
out too and there are no short circuits. With the dvm set to diode
function on the ohm scale and the neg probe on the centre pin and pos
probe on left pin the reading is 0.73 & 0.64 with the pos probe on the
right pin.


Measure the bias currents into the 'base' leads... somehow,
somewhere, there's too much, usually a leaky, perforated
driver.
__
Steve
..