Vintage Synth Repair

Hi,

every once in a while my MicroMoog all of a sudden goes out of tune. 
It happens all of a sudden and an octave is not an octave any more. 
When I hit it slightly on the side, it´s OK again, so I assume it 
might be somee loose cable ....

Maybe someone can give me a hint what to do about this, resp. where 
to look (I don´t have schematics....)

Thanks

Uwe