I have an Ikelite A100A substrobe that won’t fire. I need to open it to investigate the problem ( with all applicable precautions against the voltage across the capacitor that can be lethal). I have manage to remove the front end. The PCB with the tube on it can slide on groves, so that its position corresponds to the coverage angle that is set with the knob at the rear end. But the board cannot come out completely, because of some mechanical lock. Does anybody know how to free it?