That implies a base-emitter short in TR3 which would normally result in the output voltage being way too high, but your 170V regulator appears to be working but just a little bit low in voltage, and the actual output voltage agrees with the voltages across the zener diodes that provide the reference for the regulator. Please could you increase the voltage range on the meter again and measure the dc voltage between the screw head at the bottom of the board (black probe) and the top end of R3 (next to R6) with the red probe. Expecting about 153V DC