since you are using line level then its easy to check input by connecting a 4 or 8 ohms speaker even a tiny computer speaker that you yank out from an old 486 comp. then check if you are putting the line level to line level input and the switch if there is seletor switch in your amp. Then to if input is OK, then there should be an output right?(use the same speaker to test) if you are using voltmeter put it to AC because its AC coming out of that spkr out from amp. If you follow all wiring directions and if no input, head is dead, if no output amp is dead. Of course it is not as simple as that, but if all possibilities are exhausted then the above is true.