Pentax SFXn upper cover/focus lock problem

My SFXn has problem with its focus lock. The focus lock does not work properly some time and the shuttter fires at wrong timing. The focusing is correct. I think the contact points of switch for the focusing motor is somewhat dirty and the switch does not engage properly at the focus lock position of shutter button. If I can remove the top cover I might be able to clean the contact points. Does someone have any suggestions?
I can find 6 screws. There are 2 screws each under the neck strap fittings and 2 more at the bottom corners of finder window. Are there more screws I have to remove? Please give me some suggestions. Thanks.