If you are having issues with your SMC (Super Multi Coating) Pentax-M lenses this repair video will help. This disassembly video works for the 50mm F1.7 and F2 vintage lenses but, most of the other lens designs in the 28mm, 35mm and 20mm are very close the same.
Some info on the SMC Pentax-M 50mm f/1.7:
Optics: 6 elements in 5 groups. Pentax Super Multi-Coated.
Diaphragm: 6 blades, stops down to f/22. Full, and sometimes half-stop clicks.
Filter Thread: 49mm.
Close Focus: 1.5 feet (0.45m).
Maximum Reproduction Ratio: 1:12.5
Size: 2.5″ diameter x 1.2″ long (63 x 31mm), rated.
Weight: 6.457 oz. (183.05g), measured. 6.52 oz. (185g), rated.
Thanks to Tuber Matt Bierner for the great how to video for repairing these great vintage lenses.
Some of the tools needed for the breakdown of the Pentax 50mm f/1.7 SMC-M. is – jewelers screwdriver set, cotton swabs, Isopropyl alcohol or nail polish remover as cleaning fluid, micro fiber cloths for wiping down the lens elements, camera lens spanner tool, and a hard, well lit working surface.