You can check them by putting a meter across pin #28 and #27 of the pic (28 pin chip) should have ~ 3.3 volts. Across Pin #8 and pin #5 of the st485 should have ~ 5 volts.
But shorting the output wires should not damage them as the power on the outputs does not go through them. It is direct from the cat5 to the output.
RJ