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When does a cracked capacitor solder joint in a low voltage supply cause an amp to be completely silent? When it's a Super Champ X2 and the capacitor is the 4700uf smoothing cap in the 3.3v supply. Except that the 3.3v supply measures fine with a DMM. Not so on a scope, where it looks a tiny bit spiky. So, the spikes trigger the transient muting circuit which silences the amp. Flip the board and there's a microscopic crack around one leg of the cap. Not enough to totally disrupt the DC, but enough to generate some noise. It sounds a quick fix, but wasn't because I'd relied on my DMM and thought the voltages were all OK, so went on a wild goose chase. All the chase without the geese.