the connection on the PSU that goes to the floppydrive

this one here. (this photo is from my s900 but the 950 look the same). Be careful with this connection cause unlike the other connections on this board it DOESN'T have this little "heel" you need to press. There is still a "heel" on this connector. you loosen it by slightly push the connetor itself or use a small flat screwdriver. This construction is really made to break at some point or if you often deconnect it.

It MIGHT be the problem (just like my unit had this problem) but it can be a floppy drive defect as well. 

http://sp1200.myfastforum.org/about1662.html