Reverb problem. Help please

[Cack]

The reverb on my JCM900 isin't working and i'm not sure how to fix it. I've opened up the pan and the 3 springs are hooked up grand and all the wires inside it look soldered to the contacts. Anyone any ideas? It is fairly old and looked a bit dusty when I opened it, would a cleaning it out help? Also does anyone know if the red wire goes in the In or the out?

thanks