Hi Jag-Stangers, I unfortunately lent my Boss SD-1 to a young friend who returned it to me months later telling me that it no longer "worked" in effect mode. Nothing has been modded on this box (yet) and the led lights up when using a battery or power supply. Upon opening it up I found D1 (Zener Diode) had been cooked and left a little scorch mark in the PCB (not too bad) and the plastic coating. He wouldn't admit to it, but I know that he has one of my Line 6 effects boxes with a 9vac adapter and I figured that he tried to power the DC pedal with it without understanding the effect of AC on a DC circuit yet (I'm sure that he will tell me that it fit quite nicely). This box is from 1981 so I did change out one of the Electrolytic Caps (C17) that looked slightly puffy as well as the Diode. I don't have a 11V 500mW Zener on hand and wondered if I can replace it with a 1N4004. I've ordered a Zener just in case. The cords that I am using have all been tested and the led lights up despite there being no sound. When swapping out the Zener with the 1N4004 I still have red led and no sound in the "effect mode." What other things should I be looking at in the chain and without a scope how could I test the various paths or components with a DMM. I understand circuitry farely well but have not had as much exposure to diagnostics and would greatly appreciate some guidance. Thanks so much.