When turning on and after waiting few secs for the delay circuit, then a reassuring click emanates from the output relay if all is well. Qa is the relay coil's driver transistor. Qa BC550C should show healthy Vbe, Za Zener should show 9.1V across its legs, Dd flyback diode should show the coil's working voltage across its legs. Somewhere around the nominal 12V. With enough +/-V margin, no problem.