I don't know if you can fix it yourself or not. It will require soldering parts to the circuit board, I'll bet my lunch money.
Leaving it running is not going to hurt it.
Look closely at the cone of the speaker when you turn it on. If the cone moves one direction and stays there, along with a loud hum, then your output stage is blown, and there is DC voltage on the speaker. DOn;t leave that on.
If the speaker seems to stay at rest but hums loud, you may just need a filter cap resoldered. or maybe replaced.
Byond that, it should not be complicated for e technician to repair.
Leaving it running is not going to hurt it.
Look closely at the cone of the speaker when you turn it on. If the cone moves one direction and stays there, along with a loud hum, then your output stage is blown, and there is DC voltage on the speaker. DOn;t leave that on.
If the speaker seems to stay at rest but hums loud, you may just need a filter cap resoldered. or maybe replaced.
Byond that, it should not be complicated for e technician to repair.