How to know if a SCR is still working?
A SCR has a PNPN doting scheme. So, between gate and cathode, there is a single PN junction and that one has to have continuity at a voltage drop of about 0.7V – same as a simple PN diode.

You have to measure between anode and cathode to check if the SCR conducts when it hasn't a gate current. Without an oscilloscope, you have to de-solder it to do a simple conductivity test.