Hey folks. A relative gave me a cheap, used, 20W solid state amp they picked up at a garage sale as a holiday afterthought. When switched on it hums, but when jacked into a guitar (with unshielded electronics) it plays nothing except the faint sound of the radio under the hum, either through the primary input or the aux jack. It also has a LED light that doesn't come on when you push a Clean button. Twisting the volume increases the hum for a few seconds, then it fades

I opened the case and everything is soldered alright from the circuit board to the power supply and speaker, seemingly correctly. I suspect the circuit board has some sort of short in it that explains all this, and it needs more help that a soldering iron. But if I have described some obvious problem I just missing, feel free to let me know. Was kind of them to think of me, and always possible I'm missing something.