FOUR-PARTY SET.
(Diagram No. 3.)
Tests of the transmitting and hearing circuits can be made in very much
the same manner as in a straight set. On account of the relay coil
being bridged between No. 2 and No. 3 terminals of the induction coil,
a four-party desk set, if in perfect order, will give two hook clicks,
no matter how it is poled.
To make a perfectly sure test for primary and secondary crossed
together, it is necessary to disconnect one terminal of the relay
winding; then with the receiver on the hook, test from the L2 post to
the secondary with your head receiver; if you get current there is a
cross.
Reversals of the three wires at the top of the instrument may cause a
variety of troubles, just as in the two-party sets.
Ringing Circuit.
=Relay=: Failure of the relay to come up when the operator rings may be
caused by:
Condenser open.
Relay short-circuited or open.
Hook contacts, or red and white strands of desk stand cord, or primary
and secondary of induction coil crossed together.
Primary open.
Trouble at central office.
Test just as though it was a straight set except when testing for
relay short circuited, or for a cross between primary and secondary,
(in which case you must open one terminal of the relay winding, as
previously directed); and except when testing for relay open, which you
can do by bridging your head receiver from L2 post to No. 2 and No. 3
terminals of the induction coil successively; you should get strong
battery on No. 2 terminal, if the relay is all right and a strong
condenser discharge when you make contact, but a weak battery click
when you break contact, on No. 3 terminal.
A ground on the ground side of the line may also prevent the relay from
operating, by carrying the generator current off to ground before it
reaches the instrument.
If the relay is held up, usually the lamp is kept burning at the
central office also, and this means that current is flowing from the
central office over the battery side of the line, passing through
the relay winding, and returning to the central office over the
ground side of the line, or through the ground wire and ground. This
condition may be due to:
1st. Winding of relay crossed with frame. Test by disconnecting the “A”
or “B” terminals of the ringer from L2 which should release the relay.
2d. As in the case of current through the ringer of a straight set,
the trouble may be caused by receiver contact of hook not breaking,
white and green strands of desk stand cord crossed together, condenser
short-circuited. Test as though it was a straight set.
[Illustration: Fig. 3.]
If the relay vibrates continuously the winding is probably crossed with
the frame. To find out whether this is the case, disconnect the ground
wire, which should stop the vibrating.
If the relay “jumps” while the operator is ringing, instead of pulling
up and staying up as long as the ringing current continues, the relay
may be weak, due to a part of the winding being short-circuited out,
or to some other cause; or there may be too many bells and relays on
the line, so that, owing to the resistance of the line, not enough
generator current will flow over it to divide up and give each bell and
relay a proper amount of current; or there may be a slight ground on
the line, which carries off a part of the ringing current.
To prove that a relay is all right:
1. Short-circuit the condenser; this should hold up the relay, by
putting battery current through it.
2. Prove that the spring contact is not crossed with the frame as
follows: Disconnect “A” and “B”, then connect the frame of the
relay to battery with a test cord, and bridge from the spring
contact to ground with your head receiver; if you get no current
there is no cross.
3. Prove that the winding is not crossed with the frame as follows:
Disconnect “A” and “B” and then test with your head receiver from
the frame to the L2 posts; if you get no battery there is no cross.
=Ringer=: If the relay comes up, but the bell does not ring, the
trouble may be due to:
Ringer poled wrong.
Bias spring too tight or too loose.
Ringer open.
Ground open.
Ringer short-circuited.
Bridging your head receiver across the ringer while the operator is
ringing will show whether or not you are getting generator current on
the terminals of the ringer winding; going in series at the “A” and “B”
terminal will show whether or not you are getting current through the
ringer.
To prove whether a ringer is open or not, connect “A” to battery, hold
the relay closed, and then test from “B” to ground with your head
receiver; if you get no current the circuit is open; prove that the
open is in the ringer itself by testing direct from the two terminals
of the winding successively.
The ground can be tested in the same manner as on a two-party set.
To prove that the ringer is short-circuited, connect “A” and “B” across
the line, close the relay contact, and bridge across the terminals of
the ringer winding with your head receiver; if you get no click the
ringer must be short circuited; check this test by putting your head
receiver in series with the ringer, while it is connected across the
line, and closing the relay contact; this should give you a strong
click if the ringer is short-circuited.
=Bell ringing weak may be due to=:
Poor adjustment of armature.
Poor adjustment of bias spring.
Pivot screw too loose or too tight.
Clapper rubbing on guard.
Wiring interfering with clapper stem.
“Whiskers” on magnet head.
Magnet head sticky or gummy.
Polarizing magnet weak.
One or both coils of ringer partially short-circuited.
Too many bells and relays on the line.
Ground on one side of line which takes part of the generator current
off to ground before it reaches the instrument.
Trouble at central office.
Earth currents.
To test for earth currents bridge your head receiver from the ground
side of the line to the ground; you should get no current; if you do
get current you will probably find that it varies continually, being
due to trolley cars; report the matter to the chief inspector. In
making this test be sure that the line is not in use; if the receiver
is off the hook at any station on the line you will get a false test.
Earth currents very often cause bell troubles on suburban stations,
particularly those that lie near to trolley lines; but in the city,
earth currents are seldom noticeable.
=False rings may be caused by=:
Very strong earth currents.
One coil of ringer short-circuited.
If a biased ringer has one coil short-circuited, then when it is poled
for either 1st or 2d stations it will respond to both rings; and
likewise when poled for 3d or 4th stations it will ring with either
current.
In the bell diagram No. 3 you will see that “B” connects to the spring
contact of the relay, the frame of the relay connects to the biased
side of the ringer, and the unbiased side of the ringer connects to “A.”
In the older bells, “B” connects direct to the biased side of the
ringer; the unbiased side of the ringer connects to the spring contact
of the relay, and the frame of the relay connects to “A.”
Therefore, in connecting an extension bell to a set that has no
extension bell binding posts, connect one side of the wire to the frame
screw of the relay, under the bottom of the set, and the other side to
the post at the top of the bell that “A” connects with. Or solder one
of the extension bell wires to the spring contact of the relay, and
connect the other to the post at the top of the bell that “B” connects
with. In every case the auxiliary bell must be connected across the
terminals of the ringer without being bridged around the break of the
relay. Pole the extension bell by reversing the wires either at the
bell or at the set.
=Ringer Adjustments=: In adjusting a biased ringer find out the two
points where the bell ceases to ring on account of the bias spring
being too tight and too loose, and adjust the spring half way between
these points. To locate them, slack off the bias spring until it has
no tension at all, and then get the operator to ring while you tighten
up the spring, and note the point at which the bell commences to ring;
continue to tighten the spring until the bell ceases to ring; by making
the adjustment half-way between these two limits, you will have a
margin both ways, so that if the generator rises a little above or
falls a little below its proper voltage, the bell will still ring.
The little set screw in the yoke at one end of the armature should be
adjusted so as to hold the opposite or bias spring end of the armature
a little away from the head of the magnet core; 0.02 of an inch, which
is a little less than the diameter of a No. 22 cross-connecting wire,
“In every test use a little judgment.”