Amplifier Problem - speaker channel

I have a fairly old amp, a Sanyo. I made the mistake of being lazy and messing about with input connections when the power was on. Needless to say something blew in the amp and it stopped working.

I took it apart and found several fuses inside had blown, which I have now replaced.

However, now only one speaker channel works correctly. The left-hand channel is fine, but when I plug a speaker into the left-hand channel, the speak emits a low, loud hun, one of the speaker cones gets sucked right in, and after even jsut a few seconds of the amp powered up like this, a smell of burning comes from the speaker...luckily the speaker doesn't appear to have been damaged by this and works fine through the other channel.

Any ideas what could be causing this?