Please Help......Rainsoft Water Softener Problem

I hope someone can help me. I have an older Rainsoft Water Softener that was installed in 1978. I haven't had many problems over the years. The problem I am having now has stumped the repairman. The unit is set to regenerate twice a week. I hear it run and it sounds just fine. However, the water is hard and no salt is being used. When I manually regenerate it, the water is soft and salt is being used. (I've been marking the salt tank with duct tape so I can tell whether the salt level changes.) The repairman says this makes no sense as it works the same way whether it regenerates manually or automatically. Before calling the repairman for two weeks I documented when it went off, the level of the salt and had the water tested for free at Sears. It tested soft when I ran it manually and hard after it automatically regenerated. When the repairman came, I explained all of this to him and he ran it thru a few cycles and said everything was working fine. He tested the water and it was soft. I told him that was because I had manually regenerated it that morning. He is going to come back in a couple of weeks when he's in the area. In the meantime, he doesn't want me to manually regenerate the unit. So when he comes next time, I'll have had hard water for two weeks.....I'm not sure what that's going to prove. The unit regenerated automatically last night. Again, no salt was used. Please, anyone have any ideas on what is wrong??