Check the fuses. I've owned several amps that once the fuses blew, it still produced sound kinda like you are describing. Worth a look.
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i'd try to eliminate simple causes first, which happen more than you'd think:
try swapping interconnects
try switching speaker wires/speakers
clean input rcas with deoxit--could be corrosion
if none of the above work, you might have a bad capacitator, which is easy to fix, or something more complex
your hca1000 is a good amp--the market for a properly functioning one is probably $250-300 (you might get $100 in its present condition), so depending on repair cost it's probably worth servicing