What Is This Transistor Circuit For?

[valves4amps]

Hi Lawrence, Q705 forms an arc less switch, inductances are notorious to arc when a switch is opened I.e. car ignition systems. Q705 therefore preserves the integrity of S802. The brake solenoid is on to release the brake it's a fail safe system. If the mains goes off then Q704 and Q705 turn off solenoid off no arcing. If S802 opens then C801 holds enough charge for Q705 to switch off properly and therefore arc less switching.
Dave