The device contains analogue electronics.
It switches an external device ON, when input frequency becomes high, OFF - low.
You set the 2 frequencies, and space between them by knobs and switches.
When the device malfunctions, do not turn it ON again. The longer you keep it powered, the more parts of it burn.
The device contains 2 boards. If you have spare boards, you may swap each in order to
detect the one at fault.
It is not necessary to turn ON entire external device. You may input frequency to the device by hand: use a metal wire to short, and break current between terminals 4 and 5. In order to ensure that the device does trigger, set the knobs and switches to the lowest frequency.
If even the power light does not glow, then turn OFF at once, and swap the other board.
Keep the power ON but briefly. Do not delay. If device works, you should notice this immediately.
Give us the board at fault, or entire device.
Repairs take approximately a week. - Unless urgent.
Meanwhile we may lend you a good device.
Parts are cheap. Most expensive is work.