Technical Advice - Door Chime Mechanisms

I think the attraction for me about door chimes is that they are perhaps the first piece of electro-mechanical automation that was available to average people for their homes. Just the idea of pushing a button and having some solenoids do a little job for you is entertaining.

In simpler one or two tone chimes, the instant the door bell button is pushed, the solenoid is activated via a direct path circuit and the bell sounds right away. The electrical path is a bit more complex in a 4-tone chime. As described above, the power needs to be sequenced through the distributor. When the door bell button is pushed, that turns on power to the motor that drives the distributor, the commutator starts moving, and only once the commutator touches the first contact does the chime sequence start. In models with a rotary distributor, the door bell button has to be pressed and held momentarily in order for the commutator to overcome the start resistance in the distributor assembly. All of this is entirely normal, but might seem odd to those familiar with the immediate action of simpler chimes. The start resistance in the distributor can cause a problem though. In some models the start resistance can be adjusted. Too much resistance and the distributor will not start. Too little resistance and the distributor will not stop and the chime sequence will replay indefinitely.

Some older mechanisms have a number of natural rubber parts in the unit assembly. Each subassembly is attached with rubber grommets, presumably to deaden any vibration or mechanical noise that could detract from tone quality. In addition, the caps that retain the plungers and springs inside the solenoid cylinders are often made of the same natural rubber material. Natural rubber has the nasty habit of drying out and turning brittle or crumbly as it ages—and forty or fifty years is beyond its life expectancy. As a result, these older mechanisms are in need of refreshed rubber. Rubber grommets and neoprene washers are readily available at any well stocked hardware store, so getting replacements for these parts is no problem. Doing the R&R on the grommets is time consuming but not especially difficult.

The solenoid caps however represent a different sort of problem. I recently found one vintage mechanism that was missing the plungers and springs. At first I thought the unit had been scavenged for parts, but after more thought, arrived at the theory that once the caps had become adequately decrepit, the plungers broke the caps away on the rebound stroke and were lost forever. Whether or not it happened that way, the problem remains certain that the ancient rubber caps fail. This really complicates the solenoid cleaning process described above —if removed, the caps will crumble and need to be replaced. Oh yeah--- and if the rubber washers and caps parts have decayed, there is a really good chance that the insulation on the wiring has also gone the same route.

Here’s a quick survey of some of the common mechanisms and generally how they work:

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