If you scroll up to ic-racer's post, you will find a link to thi repair manual for the very similar ST705, http://www.pentax-manuals.com/fujica...705_repair.pdf. In the troubleshooting section they list the problem "Meter needle deflects continuously". The only thing considered under this step is the Amplifier. Also all the other meter troubleshooting steps eventually lead to the amplifier. I think the amplifier is the most likely problem.
There are diagrams and a description of how to get to it, but I'm not sure I'm ready for that.