DC Motor
tornado,
most SCR based DC motor control is woefully inefficient, has a crappy power factor and is usually supplied by an AC front end, switching the SCR at different points of the waveform to control the average DC to the armature. If that is the case, its a PWM at 2x line frequency. If its broken, I'd take the opportunity to go for a more efficient solution.
If you must repair it and its not that complex (it sounds a fairly simple circuit), redo the schematics as it stands, then repair it, so you or the person following you will not be back to the same problem as now, should it fail again. Trying to shoehorn the same parts for a different circuit is asking for trouble.