Vintage Synth Repair

Hi

I own a Moog Opus-3. Has anyone heard of a problem of the organ and 
brass working but not the strings? It seems no one can tell me what 
the articulator does what does it do? The strings and organ work in 
mode 1 but not in 2 but you can hear the strings come through in mode 
2 but you can't play them you can just hear it decay.

any ideas?

Thanks,

Tim