Is there a tape 2 monitor path? Or a preamp loop before the amp? Tape 2 monitors usually are a loop, meaning if you engage the tape 2 monitor, but have nothing hooked up to it, then no signal is passed from the output, to the input, which then goes into the power amp. An EQ loop works the same way, if the loop is activated, but not completed, then no signal will make it to the amp.