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When The Bell Doesn’t Ring

—corroded button contacts or loose connections are usually at fault
 
You're finishing your morning coffee, and are disturbed by a loud pounding noise from the vicinity of the front door. You rush to open it and find the postman with a package in his hand.

"Whassamatter, Bill?" you ask. "Why didn't you ring the bell?"

"I pushed the button about a dozen times, but nothing happened. Saw your car in the garage, so knew you were still in. Here, sign for this, will you?"

"Bell   doesn't   work?"   you   mutter.
 
`'Lemme try it." You do, and it doesn't. That evening you have a small repair job to perform. That is, it'll be small if you know your bell wiring arrangement.

In many older houses the general scheme of Fig. 1, page 72, prevails. The source of power is a bank of No. 6 size dry batteries, usually three or four of them connected in simple series. The front door "button" is merely a momentary contact switch which, when pressed, closes the circuit to a bell. If a side or rear door is customarily used for deliveries, access to a yard or driveway, etc., another button is located here and it operates a buzzer. Any number of bells or buzzers can be hooked in to work off a single bank of batteries.

Bell-ringing transformer invariably is located close to the fuse box; to make a quick check on it, set Handitest (see Testers And Tools) to 30-volt AC range and connect test leads to binding posts. This one reads OK.
 
Located near the garage door in the basement, this transformer was shaken up a good deal; it, like yours, perhaps, requires periodic tightening. Use lock washers or tie down with tape to remedy.

Exposed bell buttons are usual cause of failure of the signalling system. Inspect frequently; to get at connections, remove two mounting screws.
 
If short-circuiting button terminals with screwdriver makes bell ring, internal contacts are defective; new button is the simplest way of restoring service.

In most houses built during the last couple of decades the batteries are replaced by a small step-down transformer. The primary side, identified by its heavy black and white covered wires, is connected permanently to any of the branch circuits supplying power to the house. The secondary side, identified by its two knurled head binding posts, is connected to the bell, buzzer, or chimes through door buttons, exactly as in the battery arrangement. See Fig. 2, page 72.

The transformer reduces the 115-volt line voltage to values ranging between 6 and 16. These have absolutely no shock danger, so it is not necessary to "kill" the transformer circuit, by opening the branch fuse to •which it is connected, when you shoot trouble in the bell and button wiring.

"If the transformer is connected permanently to the line, doesn't it draw power all the time?" This question is probably framing in your mind. Yes, it does, but the amount is so small that it hardly overcomes the friction of the bearings in the watt-hour meter. When a door button is pressed, a bell or a chime takes a few watts, but for such a short time that they add virtually nothing to the monthly electric bill.

The case of the transformer may feel very slightly warm to the touch. This is normal. It does not indicate overloading, but only the internal molecular friction of the iron core of the transformer as the alternating current goes through its periodic reversals. (See "The Power System in Your Home.")

Because they are activated for only a total of perhaps minutes over the course of a whole year, the bells, buzzers and chimes themselves rarely give trouble. If one fails to work, check these points:

1) The source of power. Dry cells last a long time, but they do dry out eventually. The usual sign of impending failure is an outcropping of a white chemical around the case. A dry cell in good condition measures l½ volts. Three in series should check to 4½ volts, four in series to 6 volts. The Handitester, set for DC measurement, is fine for the job. If the batteries are more than a year old they should be suspected of weakness and then checked for voltage.

Above, a common arrangement of bell and buzzer in older houses using dry cells as source of power.

The rated secondary voltage of the step-down transformer is usually marked on the case. Set the Handitester for AC on the 30 volt scale, connect the test leads to the brass binding posts, and you'll know in an instant if the transformer is putting out juice. It isn't necessary to disconnect the existing wires to the posts for this test.

If the meter shows no voltage, disconnect either of the wires to the binding posts, open the primary power line circuit by removing the line fuse, set the Handitester for LO ohms, and try a continuity check on the secondary winding. If it's OK, it will show either zero ohms or a barely perceptible fraction of an ohm. If the needle doesn't move, the secondary winding is either burned out (an unlikely prospect), or one of its connections inside has corroded loose. A replacement transformer is then the obvious answer.

If the secondary is OK, you can run a similar test on the primary. To do this, leave the line fuse out, open the cutout box and find the primary wires, and then remove either one from its present connection. With the Handitester still set for LO ohms, again make a resistance measurement. If the primary winding is intact, it will register perhaps 25 ohms or so; if it is open, the meter needle won't move. Now you know positively if the transformer needs to be replaced or not. If it checks OK, reconnect the primary wire, close the cut out box, and replace the fuse.

Of course, it is assumed that the fuse in the transformer circuit is a good one, not that this is always the case! I once spent a frantic and thoroughly frustrating hour checking every inch of a simple bell circuit, until I had the inspiration to test the fuse. There was no reason for it to be open, but it was.

2) Loose connections. The nuts on many bell-ringing transformers do not hold very well, and are known to loosen if the unit is near a much-used door. Reinforce them with lock washers, or tie them down with strips of tape of any sort. Also inspect the screw terminals on the bells and buzzers.

The wire universally used for bell connections is No. 18 solid, with cotton or plastic insulation. Handle it carefully, as it has a tendency to break off if nicked or bent too sharply.

3) Push buttons.    If the contacts are made of iron, as they are in many cheap buttons, they are bound to rust; if they're of brass they can still corrode and get dirty. If the batteries or transformer tested OK, unscrew a suspected button from the door frame and carefully pull it away so that you can get at the terminals.    If they're rusty and pitted, don't be surprised. Scrape them off a bit, and short circuit them with the blade of a screwdriver.    If the bell comes to life, you know what's at fault. ·

In newer homes, a step-down transformer is permanently connected to the 115-volt line and supplies voltages between 6 and 16 for signalling devices. The transformer itself draws little current from the line.

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