I have 3 Cybertwins, 2 work fine and  one that powers up and all the knobs move and are active but the master volume. There is a slight pop when turned on but nothing from the input. There is a signal from "send" the output MOSFETs are heating and some times the amp will go to ten, then lots of sound. Replaced tubes, checked for ribbon connections, reformatted CMOS, Any ideas?