CHAPTER IV.

HOW TO TEST FOR AND CLEAR TROUBLES IN PRIVATE BRANCH EXCHANGE SWITCHBOARDS.

=Station can’t call=: When a station can’t call, the trouble may be due to the line being open, or too much resistance in the line; or to the signal being open, or short-circuited, or stuck.

Short-circuit the line in the back of the switchboard or at correcting frame; if the signal does not operate plug up the jack with a plug and see if the cord signal will operate; if it will not the open is between the frame and the springs of the jacks if the cord signal will operate, the trouble is back of the jack springs, and may be an open, or it may be that the drop is short-circuited or stuck. Test with a receiver or lamp, if you get good battery on the locknuts but can’t throw the drop, it must be short-circuited or stuck; if you get no battery there is an open; short-circuit the inner contacts of the jack, and if this brings up the signal the open is in the jack; take the jack out and repair it. If short-circuiting the inner contacts will not operate the signal, the same may be open; test from the ground strap of the jack direct to the signal terminals; if the signal tests all right the wire leading from one side of the signal to one inner contact of the jack must be open; prove by short circuiting same out with a test cord.

If there is battery on the jack but the signal won’t come up, push gently against the back of the armature of the signal with a tooth pick until it starts to raise; you can tell by the feeling if it is at all stuck.

Another good way to tell whether the signal sticks is to go to the station and hold the receiver to your ear and then allow the hook to raise. When the signal flies up it can be heard in the receiver as a sort of “tremble.” This “tremble” should take place the instant the hook comes up; if it is delayed, the signal must be sticking.

This test can also be made from the frame with a head receiver.

To test whether the signal is short-circuited, see how brightly your lamp burns when connected at the frame and then compare with other signals which are all right; a signal which is wholly or partly short-circuited will have less resistance than the others, and the lamp will burn brighter.

If the signal comes up from the frame but will not come up from the instrument, the line may have too much resistance and the signal will have to be adjusted so as to be more sensitive.

If a station on a long line has trouble calling at times, there may be a poor connection in the circuit which varies; or it may be that the signal fails to work only when the board is busy, due to the drop in voltage on the battery feed when much current is being drawn from it; the signal will have to be adjusted more delicately or the battery feed increased.

[Illustration: Fig. 4.]

=Station Signal Stays up=: The line must be either crossed, or grounded on the battery side. Plug into the jack with a detached plug and cord, and then test successively on the ring and tip of the detached cord with a receiver or lamp that is connected to battery. This will show if there is a ground on either side of the line. If both sides test clear of grounds, there must be a cross; to prove this, ground the tip side by holding the tip of the detached cord on the tip of any other plug; if there is a cross the ring side will then test grounded. To locate the trouble, open the line successively at the frame cable box instrument, etc., and note the effect on the signal.

In testing with a receiver for grounds or crosses on lines, you should be guided by the click when you break contact; otherwise, you are likely to be deceived by the electrostatic capacity of the line and condenser in the instrument. In such tests you may get a strong click when you make contact, particularly if the line runs through a cable, and you may also get plenty of induction on the line; but if you do not get a click when you break contact, there is no current flowing through your receiver, and therefore the line is clear.

If plugging into the jack does not restore the signal, the trouble must be a cross in the jack, or in the signal itself. Examine the jack lugs, and also the inner end of the signal winding, which may be in contact with the iron mounting strip. If the trouble is not here, disconnect the wire going to the jack from the signal; this will show whether the trouble is in the signal itself.

If the sleeve of a station jack is grounded, the cord circuit relay will operate when you plug into the jack, and cut the battery off of that pair of cords. Touching the tip of a plug to the sleeve of a station jack with the listening key thrown will show if the sleeve is grounded by giving a click in the operator’s receiver, the same as touching the sleeve of a trunk jack will do. The ground may be due to the sleeve being crossed with the sleeve of a trunk jack, or crossed with the sleeve of a station jack that is connected to a trunk jack; or it may be between the sleeve and the inner contact of the jack on the ground side.

=Battery Feed and Trunks=: The battery feed and trunks must always be poled properly. To test the poling of the feed, run a temporary ground and touch it to the ring of the back plug. If this does not bring up the cord signal the feed is poled wrong, and the feed and ground will have to be reversed.

To test the poling of a trunk, plug into the trunk-jack with the front plug of any pair, say No. 1 pair; then touch the tip of any other plug to the ring of the back plug of No. 1 pair; if this does not bring up the cord signal on No. 1 pair the trunk is poled wrong.

One of the troubles caused by the wrong poling of a trunk is that if the operator plugs in to answer the trunk while she has another listening key thrown, her transmitter goes dead.

If operator at the central office can’t throw a trunk drop at a private branch switchboard the same may be open, or the condenser may be open. Bridge a receiver across the drop; if you can get a good ring in the receiver the condenser is all right and the drop is probably open. If you can’t get a ring across the drop, short-circuit the condenser; if this puts battery through the drop and brings it up, the condenser must be open.

If a cord circuit relay fails to operate on any trunk, the ground strap may be broken off of the jack. Plug up the jack, then touch the butt of the plug with the tip of a plug of any other pair; if this operates the relay, it shows that the sleeve of the jack did not operate it, and therefore the sleeve connection must be open.

The sleeve connections are often taken off purposely on tie trunks.

If the operator complains of central cutting her off, some of the holding coils may be open. Instructions are given further ahead for testing them.

If plugging up a trunk causes the cord circuit relay to vibrate the battery feed or ground must be open.

If the line or cord signals fail to come up properly the battery feed may be weak; this may be due to a poor connection in the feed or ground, or to one of the conductors of the feed being open, or to the feed being grounded through resistance. Bridge a lamp across the feed; it should burn brightly if no current is being used on the switchboard. Throw a listening key, or bridge a receiver across the feed; if this puts the lamp out, or dims it excessively, the feed or ground has a high resistance on it, or some of the conductors are open. Disconnect the conductors one at a time at the table head or protector, and see if each one will light your lamp properly. If the lamp burns dimly when no current is being used on the switchboard, the feed is probably grounded through resistance; disconnect it from the switchboard and test; if it still gives a dim lamp disconnect at the protector and test again to prove whether trouble is inside or outside.

The amount that a lamp bridged across a battery feed will be dimmed by throwing a listening key or bridging on a receiver depends upon the resistance of the feed. If the feed is very long the lamp will be dimmed very much; if the feed is short or consists of several pair, the lamp will be dimmed but slightly. Each inspector should become familiar with the behavior of the battery feeds on all his important boards; he should know how the lamp burns when the board is idle, and how much it is dimmed when a certain number of connections are up, so that in case of trouble he can tell at once by a lamp test whether the feed is O.K. or whether it has too much resistance, or is partially grounded.

Troubles Causing Bells to Ring.

A swinging open or swinging ground on the battery feed causes the bells at the stations to ring by charging and discharging the condensers.

Generator feed crossed with the battery feed causes bells to ring. Examine wiring and generator contacts at ringing keys.

Where the spring of a station jack does not break from, or is crossed with the inner contact, all bells may be rung by ringing on that jack with power generator, which is always grounded on one side.

If the outer contact of a ringing key makes before the inner contact breaks, all bells may be rung when that key is used, by the generator current passing down through one side of the retardation coil to the battery feed.

Cord Circuit.

Tip and sleeve crossed causes vibrating relay on that pair.

Tip and ring crossed short-circuits the cord.

Ring and sleeve crossed causes relay to vibrate when ring and tip of plug are short-circuited, or when the plug is put in a station jack with the station receiver off the hook,—sometimes merely throwing the listening key on that pair will make the relay vibrate.

Touching ring to tip and tip to ring of the two plugs of any pair should give a spark, and the signal should also come up when the ring of the plug is touched with a tip. If there is trouble, take any other plug which is O.K. and test the bad pair; if both rings or both tips fail to give a spark, there is probably an open at the relay, the retardation coil, or the soldered connections on the listening key. If only one cord tests open, and the other one of the same pair tests O.K., ring on the bad cord and feel for generator current in the plug. If you get current, the open must be at the inner contact of the ringing key; or, it may be in the cord signal. If you cannot get generator on the plug, the open is in the cord.

To locate any open that effects both cords, test successively on inner contacts and swinging contacts of relay, inner and outer lugs of retardation coil, and swinging contacts of listening key, you should get battery across all of these points.

If either cord of a pair is short-circuited it short-circuits both cords and you will not get proper sparks when touching ring to tip and tip to ring but you may get small sparks. Also the operator’s transmitter will be dead on that pair of cords and if you test with a receiver or lamp you will get little or no battery between the ring and tip of either plug, but will get battery of about half the proper strength from either the ring or the tip of either plug to either the ring or the tip of a plug of any other pair.

You can also tell whether a cord circuit is short-circuited by bridging your receiver around one half of the retardation coil; if there is a short-circuit, part of the current that is flowing around through the coil will go through your receiver, giving you a click.

To locate the short-circuit, ring on the two cords successively, and feel on the plugs for generator. If both cords test clear, the trouble must be back of where the circuit branches at the listening key; disconnect successively at the relay, the retardation coil, and the listening key until you locate the trouble.

In most of the private branch exchange switchboards the battery goes first to the inner contacts of the relay, then through the swinging contacts to the retardation coil, and from the retardation coil to the swinging contacts of the listening key; in other boards the battery goes first to the retardation coil, then through the relay contacts to the listening key. From the listening key it goes to the inner contacts of the ringing key, and from the swinging contacts of the ringing keys to the cord fasteners.

If a cord circuit is open at the relay or retardation coil, it will still work on a trunk connection, the trunk supplying the battery, if the central office is common battery system.

Lamp tests of the retardation coils and cord signals can be made by bridging a lamp across the bus-bars and then short-circuiting the tip and ring of every cord successively. Each one should dim the lamp the same amount; if one cord dims it less than the others, it shows that there is more resistance in that cord circuit—possibly a bad connection, or a cord signal with too much resistance. If one cord dims it more than the others, there must be less resistance in that cord circuit, probably one half of the retardation coil is short-circuited. (This test fails where there is a floater battery, or a battery feed of very low resistance.) To prove that one side of the retardation coil is short-circuited, short-circuit one of the plugs of that pair, and then bridge a receiver successively around the two sides of the coil, no click on one side should mean that that side was short-circuited.

A finer test can be made by bridging the lamp across the tip and ring of the cord, and short-circuiting out the two sides of the coil successively; each side should brighten the lamp exactly the same amount. If one side brightens it more than the other, that side has more resistance than the other.

Unbalanced coils are usually noisy, especially on long lines. An unbalanced coil can usually be detected by simply listening on each pair of cords, successively; if the battery feed induction is stronger on one pair than on the other, that pair is probably unbalanced.

In most boards the holding coil is bridged across the outer contacts of the relay. In other boards one end of the coil connects to one swinging contact of the relay, and the other end to the opposite outer contact. To test the holding coil, plug into a trunk jack with the back plug and throw the listening key, which will bring up the cord signal, then throw the listening key normal. If the signal stays up the holding coil is O.K., if it disappears the holding coil circuit must be open. The trouble may be that the relay contact does not close, or the coil itself may be open.

Test by plugging into a trunk with the back cord and then short-circuiting the holding coil; if the cord signal comes up the holding coil must be open; if it does not come up, leave the short-circuit on the coil and bridge out the holding coil contacts of the relay. When you bridge out the contact where the open is, the signal will come up.

To test the relay on any cord circuit, touch the tip of any other plug to the sleeve of either plug of that pair; if this does not operate the relay the sleeve conductor of the cord may be open; if neither plug of the pair will operate it, the relay itself may be open; test with a receiver or lamp.

Touching the tip of one plug to the sleeve of the other plug of the same pair should make the relay vibrate.

To test a switchboard cord, plug into the cord testing jack (every board should have a testing jack connected to put battery direct on your head receiver) and shake the cord, and turn and shake the plug in the jack, while you listen in the operator’s receiver for any cut-off or bad connection. Do not have any listening key thrown while you are testing switchboard cords; also see that the operator’s receiver is poled so that the current from the cord strengthens the magnetism instead of weakening it otherwise you will not get a sensitive test. The tips and rings of the plugs must be clean, or else they will be scratchy.

Be very careful that none of the plugs are bent or “lopsided;” such plugs may work all right in some jacks and cut-off in others. If turning a plug around in a jack causes a cut-off the plug should be condemned; sometimes the jack may be at fault, and the long spring will have to be given more “set.” After changing switchboard cords, always test the new ones for opens, short-circuits and reversals.

=Cross-Talk=: Solder dropped on the cord fasteners, or a cross at the keys, may connect two different cord circuits together, and cause cross-talk between them.

Retardation coils may be crossed with their cases, and cause cross-talk by the cases being in contact. Condensers on trunk drops may make two trunks cross talk in the same way. Test by bridging a receiver from the case of the suspected coil or condenser to battery and to ground successively. There will be no click if the case is clear.

Unbalanced retardation coils, or a weak battery, may also cause cross-talk.

A listening key that does not break contact on both sides will cause cross-talk when that pair of cords is used; if with all keys normal you get a click in the operator’s receiver when you touch the tip of any plug to the frame of the operator’s transmitter, the operator’s circuit is in contact with some cord circuit at the listening key. To find out which key, see that all keys are normal and then vibrate the relay on each pair of cords successively by touching the tip of one plug to the sleeve of the other; when you come to the pair where the cross is, the buzz will be heard plainly in the operator’s receiver; on the others it will be heard very faintly.

=Operator’s Set=: To test the receiver cord, put a plug in the cord testing jack, this puts battery through the receiver, and by shaking the cord any fault will show up provided the receiver is poled properly. Do not have any listening key thrown when making this test.

To test the transmitter cords, throw up any listening key and listen in the operator’s receiver while you shake the cords.

To locate an open in the operator’s primary circuit, throw any listening key, and then bridge a receiver successively around the several parts of the circuit, that is, the 200 ohm resistance coil, the transmitter, (including its cords), and the primary. When you bridge around the part that is open, you will get a click in the receiver.

To locate an open in the secondary circuit, short-circuit out the condenser so as to get battery through the circuit and then bridge around the receiver and secondary with a receiver until you have found where the open is.

=Buzzer and Buzzer Relay=: If a buzzer which works off the battery feed fails to operate at times, although the buzzer relay comes up, probably it is not sensitive enough, and when the board is busy the battery feed it not strong enough for it. Adjust the buzzer more delicately and test it when the board is idle and when it is busy. To make a board busy artificially, bridge a head receiver across the bus-bars; that is equivalent to several pairs of connections being up.

If some of the station lines are very long, the buzzer relay may fail to come up on them, or come up so weakly as not to make good contact. To cure this, adjust the relay more delicately.

If a trunk drop won’t operate the buzzer relay when the key is up, the trouble is probably at the night bell contact of the drop. If none of the trunk drops will operate it, the relay may not be adjusted delicately enough, or the 500 ohm resistance coil may be open. Bridge around the trunk drop contacts with a receiver. If you get no battery the coil must be open; prove by bridging the coil out and repeating the test.

A heavy ground on the ground side of any station line will prevent the buzzer relay from coming up by shunting it out. A light ground will sometimes cause trouble on the long lines only.

A short-circuited condenser or a slight leak across any line or lines, may hold up the buzzer relay. Test the lines for crosses and grounds, as previously instructed. If the buzzer relay comes up at times when no signal is up, the trouble may be due to some station on a long line trying to call, and the signal not sensitive enough to come up.

General.

To prove that a board is perfectly clear, disconnect the battery feed from the negative bus-bar, and put a lamp or receiver in series. If you get no current then all the lines are free from crosses, they are free from grounds on the battery side, and the other circuits in the board are also clear of crosses. (This test can only be made when there are no connections up, no listening keys thrown, and no stations calling.) To prove that the ground sides of all the lines are clear, disconnect both the feed and ground wires from the bus-bars, and then test through a lamp or receiver from the battery feed to the ground bus-bar; if you get no current, the lines are all clear on the ground side.

INSPECTION

How to Inspect Subscribers’ Instruments.

1st.—Ask the subscriber if his instrument works properly and repair any defect that he reports. Also be sure the instrument is securely fastened to the wall or desk.

2d.—Clean and polish the varnished and nickeled parts of the instrument; open the bell and see that it is clean and in proper condition inside, and that the hook, ringer, and other moving parts work properly and clean the hook contacts with paper if they are dirty or make a scratching noise in the receiver.

3d.—See that all binding post connections are tight, test all cords; in testing the receiver cord, put battery through it by short-circuiting the condenser; change any cords or other parts that are defective or unsightly.

4th.—Clean the receiver outside, remove the cap and examine the diaphragm and clean the magnets; in cleaning the magnets rub them off with your coat sleeve or a clean rag rather than with your hands, as the moisture from your hand will cause them to rust.

5th.—Examine the adjustment of the bell and test by getting a ring from the operator, at the same time test the transmission and hearing.

Test all extention bells by getting a ring from the operator; inspect all other apparatus, such as hand generators, switches, local batteries, fans booths and signs. It is important that signs should be kept in good condition; dirty or unsightly ones should be cleaned or ordered changed, and you should be particularly careful to see that all signs are securely hung.

6th.—Inspect all wiring, including the leading in wires, the inside line wires, the battery wires and the ground wires; also the protection, the fuses, any extention bells and also see that the ground is properly made that it is connected to the proper pipes. If a gas pipe has been used see that the bridge on the meter has not been disturbed since the last inspection.

7th.—See that the protector contains the proper kind of fuses, and if it can be gotten at readily; examine the connections and remove the cap from over the carbons to see that no one has left the carbons out.

8th.—If a subscriber applies to you to have an additional instrument installed, take his name and address and turn them in to the manager; if he wants his telephone moved or disconnected, or circuit number changed, or extention bell or sign installed, request him to call up the managers office.

If he complains of poor operating service, or of interference by other subscribers on his line, refer him to the manager.

If he complains of some trouble that is in the outside line or at the central office, report the matter to the chief inspector at once.

9th.—In making recommendations, state briefly but plainly just what you want done and give the reason why. If the installer has done any work at the station since your last inspection, and has failed to leave it in proper condition, accompany the recommendation that you make with a written complaint.

Making First Inspections of New Installations.

In inspecting a new installation, or an instrument that has been moved or changed since your last inspection, or in going over your instruments for the first time, the inspection should be made more carefully than at other times.

Ask the subscriber if he has any extention stations, extention bells or other apparatus attached to his instrument, also look out for them while you are making the inspection and tracing out the wiring.

Open the desk stand and see that all the locknuts are tight and soldered connections are perfect.

Examine and shake all soldered connections in the bell.

Trace out all of the wiring and be sure to see that all splices are properly soldered and taped and see that no tacks are driven in the splice.

Make a lamp or receiver test of the protector and the instrument ground, to see that they are good and have no resistance.

See that the protector is securely fastened, that the connections are all tight, that the fuses and carbons are of the proper kind, and that the micas have the open side down.

Test the fuses for loose connections inside, by bridging your head receiver across the binding post at the instrument end of the protector and listening for a cut-off, while you shake and jar the fuses.

Test all switches to see that they make all proper connections, oil the hand generators and see that the bell clapper works freely.

See that the specifications have been complied with in placing the protector and the instrument, in running all the wire, and in every other particular; that the desk stand cords are cleated, and protection cleats used where needed; that desk sets give two hook clicks; that snap switches are of the indicating type; that the connections to all binding posts are neat and of proper length; that the booth is clean and have plugs in all the screw holes; that they have no broken glass and have linoleum on the floor, and that the doors and latches all work freely.

See that the protector is placed so as not to be in the way of curtains; that no damage has been done to the subscribers property; that all apparatus has been installed so that it will not be in his way, and will not be exposed to disfigurement, damage, trouble from dampness or rain, etc., that wire is run where it will be safe from injury, dampness and wear; in short, see that the installation is done according to specifications in every respect.

See that the cut-in (the wires from the pole to the house) are properly made and are of the proper kind of wire.

DON’T FORGET THAT YOUR REPUTATION AS AN INSPECTOR IS AT STAKE.

FOOTNOTE

[1] Where reference is made to “hook clicks” in these instructions, the instrument is understood to be a desk stand, wall sets are so connected as to give only one hook click on raising or lowering the hook.

When reference is made to the red, white or green strand of the desk stand cord, it is understood that the red goes to the hook, the white to the receiver and the green to the transmitter, using the standard Western Electric cord.

When reference is made to L1, L2 or G you will find them on diagram No. 1 or No. 2. When reference is made to “A” or “B” you will find them on diagram No. 3.

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Transcriber’s Note (continued)

Page 42 – “deskstand” changed to “desk stand” (Open the desk stand)

Page 43 – “lineoleum” changed to “linoleum” (have linoleum on the floor)

Footnote – “G1” changed to “G” (When reference is made to L1, L2 or G)

The words “extension” and “extention” are used interchangeably throughout the book and have been left unchanged. Some missing punctuation and other minor typographical errors have been corrected without note.

The single footnote has been placed at the end of the book.