Hi, I'm not sure this is exactly the right place to ask, given I'm not actually building it, but it can't hurt to ask. I've bought an amp off ebay; a Marshall MB30 for the low, low price of £32 shipped. The catch, of course, was it being listed as not working, for parts. So I got it, and I'm going to have a go at fixing it, and I thought I'd ask here for some pointers on how to diagnose the problem. What I've done so far: - plugged it in, it powers on, LEDs turn on, switches work, the pots seem a bit stiff but functioning; - plugged in a guitar, verified that it does not produce any sound (as advertised); - put the amp in the "Modern" channel, fiddled with the compressor, saw the LED go from green to red (assuming that means the signal hit the threshold) for different lengths of the strum (that is where I got the "pots seem to function" from); - plugged a cable from a phone into the CD in jack, got no sound to the speaker either; - plugged headphones into the headphone out, no sound; - ran a cable from the line out to another amp, got sound from the other amp; - ran a cable from the effects loop send to the other amp, also got sound. That is where I've got so far. In my layman understanding of things, this all means the preamp is fine, the problem is somewhere down signal of that. Also, given the headphone out also not getting a signal, it seems the problem is not in the speaker itself. What can I do now to track down the malfunction? I'm assuming it's now a question of cracking it open and checking how it looks inside, but some pointers on areas that are likely to be faulty would be cool. Also, am I likely to have caused fresh harm to something by running those lines to the other amp (I used an instrument cable for this)? I did keep volumes low, and only did it long enough to verify there was signal going through. Thanks!