Report "We have an older model Nutone door bell (mid '70s). It gradually quit chiming. The transformer works. When a door bell is engaged the wall unit buzzes for 3-4 seconds and than stops. We do not have an instruction manual. There is a name plate that says to unstick a plunger remove bell bar, There are 3 bell bars. Each is held by two metal rods that must be attached somehow out of sight. They turn but do not release. We have tried several approaches but cannot remove any bell bar. How dd you remove a bell bar? The mechanical unit has the number LA49F79. The wooden exterior cover has the number A67278. The interior circuit board suggests that this is a clock model"