Amp sending sound to only one speaker...

[snags]

Both speakers have been checked on another system and are working perfectly. What might be the cause of the amp problem? Thanks.

[Old_Geezer]

Dodgy connection at the speaker socket?
Blown output power transistor/whatever on the duff channel? Fuse blown?
Dodgy connection anywhere inside, say on the volume pot for instance; or a dry joint on the circuit board.
Might even be the input to the amp. Have you tried more than one source?
Must be the case that there are millions of possible causes.
Try opening it up and seeing if there is anything obvious, like a loose wire. Failing that someone with expertise would need to check (using the amp's circuit diagram) how far the signal is getting.

[snags]

Thanks O_G. I was hoping it might be something simple, which I guess it might but sods law it probably won't be...

[AlBags]

If it has the old DIN speaker sockets .. flat blade plus pin .. it will be that .. maybe.
Otherwise .. output stage blown, speaker output fuse (if it has them) or NO INPUT on that channel.

[snags]

Thanks Al...