TROUBLES AND REMEDIES

• General

There follows a table which is intended to be of help in finding the source of various troubles which may be encountered. It is important to remember that WHEN TROUBLE IS ENCOUNTERED THE FIRST THING TO DO IS TO DISCOVER THE SOURCE OF THAT TROUBLE. Consult the table which follows. Check to make sure trouble exists. Go over the possible causes carefully and make the simplest checks first. When the simpler checks have been made and the trouble is not found, check other possible causes. Read Page 101, on "Adjustments and Balances" before disassembling any parts or making any adjustment.

• Loss of Vacuum

A gyro unit may lose vacuum for several reasons. The trouble may be due to a leak, in which case it will continue to get worse, or it may be caused by volatiles within the casing. These volatiles reduce the vacuum more when the case is hot than when it is cold. For this reason the vacuum may continue to drop because the lowered vacuum results in overheating which further reduces the vacuum. Any trouble which results in overheating is likely to result in a reduction of vacuum even though the case is tight and has been properly evacuated.

If the vacuum drops and the unit overheats in service, check the gyro supply voltage. If this is normal, it will be necessary to reduce the speed of the wheels by setting the latitude dial to 50 degrees. Usually this must be done if the vacuum gauges reading drops below 29 inches. Under the reduced speed the vacuum will usually improve. If, however, it continues to drop and the compass must be kept in service, open the air valves in both gyro casings and set the latitude dial to 55 degrees.

The Ballistic Deflection will not have the correct value when the wheels are running below normal speed. This will result in a temporary error on a turn or change of North-South speed component. The error is small and damps out about an hour after the turn or speed change is completed.

The following tables are included as an aid in locating follow-up troubles. The material given here is not a detailed analysis of all possible follow-up troubles, but rather a condensed outline of tests for the most probable sources of trouble encountered in operation. If it is desired to work on the follow-up while the compass is still in operation, remove the fuses on the control panel marked "Follow-up System" and use the emergency azimuth scale for obtaining headings.

When servicing the follow-up make all the simple checks first. Look for broken or burned out tubes and loose connections. Look for foreign objects which might short out parts of the circuits. After these checks have been made, if trouble still exists, an attempt should be made to locate the defective circuit. The two meters on the front panel will help to locate the faulty section.

In using the follow-up meters to find the circuit in which trouble exists, read the tube "On-Off" indicator first (instrument on left, Figure 47). If the needle is to the left, for example, tube No. 1 should be operative. If it is not, there is something wrong with the tube or its circuit, such as a defective follow-up motor armature or follow-up motor switch in "Off" position. If the "On-Off" indicator shows no deflection but the amplifier plate current meter (instrument on right, Figure 47) shows abnormally low current indicating that a large signal is present in the amplifier tube, then the trouble lies in the interstage coupling. The plate current should return to normal (1.5 to 2.5 milliamperes) when there is no signal input.

Having determined the approximate location of the trouble, check the voltage drops across the various units in the circuit with the values shown in Figure 72. These values, the average of several tests made on different follow-up panels, were obtained while the master compasses were functioning properly, and were measured with a Weston type 301 meter having an internal resistance of 1000 ohms per volt. The units being tested should check within ± 10%. If any large differences are found, remove the fuses, as outlined above, and check the D.C. resistance of the circuit in question with the values given in the following table. These units should also check within ± 10%.

TABLE OF ELECTRICAL VALUES OF FOLLOW-UP PARTS

(Symbols correspond to those on Figures 61 and 72).

ADJUSTMENT AND REPAIR
D.C. RESISTANCE OF FOLLOW-UP CIRCUITS

* In circuits in which there is a rectifier, changing the polarity of the test leads changes the resistance of the rectifier. Generally, a rectifier will continue to function properly even though its resistance varies greatly. Hence, look for some other defective part before replacing a rectifier.

Page 99 foldout oversize drawing.
Amplifier Unit
Internal Wiring
Figure 72

ADJUSTMENT AND BALANCES

• General

All adjustments and balances are carefully checked at the factory before the compass equipment is shipped. If the equipment is properly handled and operated, further adjustment will very rarely be necessary until parts are replaced.

• In Case of Trouble

As long as the compass is operating satisfactorily, do not disassemble the parts or move any weights. When an irregularity of operation is noted, look for the cause before attempting an adjustment. Consult the table of "Troubles and Remedies", page S5, to find possible causes. Check the control panel instruments to make sure the supply voltage and frequency are normal, and that the gyro current is about 1.7 to 2.6 amperes in each phase. Check gyro voltage and D.C. voltage. See page 86 for correct values.

Go over the possible causes of trouble listed in the table, making the simplest checks first. In the great majority of cases the trouble is caused by some simple defect.

Unless a weight has worked loose or a part has been replaced, an adjustment of the sensitive element balance is very rarely necessary. Even when a part has been replaced a rebalance in many cases is not necessary. If, however, it appears that an adjustment must be made, proceed as follows:

(1) Check voltages of A.C. supply, D.C. supply, gyro supply, and gyro current. Normal values are given under OPERATION, page 86.

(2) Check vacuum readings of both gyro units. Vacuum should be about 29 inches.

(3) Check setting of latitude dial, and motor generator speed.

(4) Look to see if mercury tank oscillator is working.

(5) Go over control panel, follow-up panel and master compass, looking for loose connections, shorts, or other wiring defects.

(6) Determine whether or not follow-up system is operating by comparing card reading with emergency azimuth scale reading. The card and emergency azimuth scale read the same only when the speed corrector is set at zero. Turn follow-up motor switch off, turn 36-speed dial by hand to put error in card reading, then turn follow-up motor switch back on. Motor should bring card back immediately to its correct position. Move 36-speed card back and forth to check "dead space" which should be practically zero.

(7) Feel the gyro units to detect abnormal heating or vibration. Make sure both wheels are running.

(8) Go over adjustable weights and locknuts on sensitive element to see if any have worked loose, but do not move the weights.

(9) Go over entire sensitive element very carefully looking for screws, nuts, mercury, or other foreign material which might be resting on frame or in some unseen place, as, for example, under the damping tanks or around the damping cut-out magnet.

(10) Check position of bubble in North-South level. This bubble should be on scale after compass has settled. If it is not, proceed according to instructions on page 102.

(11) Check damping cut-out circuit to make sure valve operates when contacts close.

(12) Shut down compass. After gyro wheels have stopped turning, check freedom of gyro units about the vertical. If there is evidence of sticking or excessive friction, remove element, disconnect coupling links, check freedom of gyro case rotation and of link motion. Make certain that the gyro coupling stop screws are correctly adjusted. Normally the gyro axles are inclined 35° from the North-South axis. At the extreme outward position (using the gyro centering spring stud as a reference point) the axles are inclined 20° and at the extreme inward position the axles are inclined 42°.

(13) Check freedom of element to tilt and rotate. It should, as nearly as can be determined, be perfectly free to rotate. After a slight push it should continue to rotate for many minutes. Resistance to motion indicates bent contact pins or improper flotation.

(15) If the trouble is an error on turning, or an occasional open gyro circuit as the ship rolls, remove the spider assembly (see page 112) and inspect for bent contact pins and insufficient or dirty mercury in contact cups. The mercury in the outer cup should be 3/4 inch deep, the middle cup 1/2 inch deep, and the center guide bearing half way to the top. Be sure the mercury is clean. Before filling the cups, wipe them out with a damp cloth and allow them co dry.

(15) Remove damping tank covers and examine fluid. If dirty, flush out tanks and refill with clean oil. See page 93.

• Sensitive Element Level Adjustments

After all the items above have been carefully checked the level bubbles may be brought on scale. Be sure that the compass has been running at least four hours and has settled. Bring East-West bubble to center of scale by shifting the weight which is on a rod parallel to East-West bubble tube axis. This adjustment is not critical. If the bubble is not off center more than 1/8 inch, no adjustment need be made.

After East-West bubble is centered, or approximately so, as its position is not critical, allow compass to settle again and bring North-South bubble on scale by turning the North-South level adjusting weight. One-half turn of the weight will advance the bubble fifteen divisions when it is fully on scale.

• Pendulous Factor Adjustment

Always check the pendulous factor before making this adjustment. No adjustment should be necessary unless the weights nave worked loose or parts have been replaced. Look for other trouble first. Check all the 16 items above. Rarely is a pendulous factor adjustment necessary. If the factor is wrong there will be a temporary error on turns or upon sudden change of ship's speed. When the ship is anchored, pendulous factor does not affect the settling point.

The pendulous factor is a function of the distance between the center of gravity and the center of support of the sensitive element. It determines the undamped period of the element. This period should be the same for all latitudes when the latitude dial is correctly set. The undamped period is measured as follows when the ship is not in motion:

(1) Set the latitude dial on the control panel very accurately to the correct ship's latitude. Check the motor generator speed. See pages 85 and 106.

(2) Determine the settling point of the compass.

(3) Turn the damping cut-out switch to "Off".

(4) Precess the element 30 degrees to the East of the meridian by pressing down lightly on the South side of the element. Bring the North-South bubble to several divisions South of the settled position by pushing on the bubble tube in the direction the bubble should go. This is done so that the element will start to precess away from the meridian, reach a peak shortly, and then go back toward the meridian.

(5) Allow the element to oscillate across the meridian several times, recording the exact time when the element crosses its settling point. The North-South bubble will cross its settling position when the oscillation amplitude reaches a maximum. The oscillation should not diminish at each swing by more than about two degrees. A greater reduction of amplitude indicates excessive friction at the contact guide pin, in the mercury, or leakage of the damping fluid past the cut-out valve.

If the ship's heading is changing, as it may when the ship is anchored but not moored to dock, the oscillations cannot be determined from the card reading. The period, however, may be taken as the time required for the bubble to cross any position on the scale, come back, and cross the same position in the same direction; or relative bearings of a terrestrial object may be taken from an alidade.

From the readings recorded during the undamped oscillation, determine the time required for a complete oscillation from a peak on one side of the meridian back to the next peak on the same side. Check by determining the time elapsing from the first crossing of the meridian (settling point) until the next crossing in the same direction. This time is the undamped period and should be 85.7 minutes ±2 minutes at any latitude providing the latitude dial is set correctly.

• Damping Percentage Adjustment

The percentage of damping is a function of the rate of flow of oil between the two damping tanks. If the flow of oil is reduced, the damping percentage will be too low. Regulation of the oil flow is adjusted at the factory. This is done by changing the length of a round rod fitted snugly into the oil line. A flat along one side of the rod permits the oil to flow. No change should be made in this adjustment. Insufficient damping is due to dirt in the fluid or use of the wrong fluid.

To determine whether or not the damping percentage is correct, proceed as follows when the ship is not in motion:

(1) Proceed as outlined in steps (1) to (4) of "Pendulous Factor Adjustment".

(2) When the element reaches the peak as explained in step (4) of "Pendulous Factor Adjustment", turn the damping switch to "On".

(3) Allowing the element to precess back and forth across the meridian, record the amplitude of the original displacement and the following two peaks.

(4) The first swing past the meridian should carry the card about fifty percent of its original displacement from the meridian, that is about 15 degrees. The second oscillation should be reduced by about 80%, that is to approximately 3 degrees. The damping percentage is the average of these two percentages and should be between 55% and 80%. Unless the damping is outside of these limits, no attention is necessary.

If the damping percentage is below the lower limit, drain out the damping oil, flush out the tanks, valve, and pipe thoroughly, and fill to a depth of 1-1/4" in each tank with clean oil. See page 93. Check the damping percentage to make sure the proper value has been restored.

If the damping percentage of the compass is too high, friction to movement of the sensitive element is indicated. Check flotation and contact pins.

• Bell Crank Adjustment

Each gyro is coupled to a bell crank by a link. When the gyro units precess through equal and opposite angles, as occurs when the ship rolls, the links move and the bell crank turns. In order to preserve the balance of the sensitive element under this condition, weights are placed on the bell crank at the factory. Unless extensive replacement of parts is made on the element, this adjustment will not require changing. Gyro units are carefully balanced about the vertical and horizontal axes so that changing these units does not necessitate a readjustment of the bell crank weights.

If extensive repairs have been made on the element, or if the weights have been removed and it is desired to check the balance, proceed as follows:

(1) Shut down the compass and let the gyro wheels stop rotating.

(2) Turn the damping switch to the "Off" position and level the element by placing several small weights about the element.

(3) Remove the gyro centering springs. Be sure the element is floating properly.

(4) Turn the gyro units so that the coupling links move away from each other to their extreme position.

(5) Let the element come to rest. Note position of East-West and North-South bubbles.

(6) Turn gyro units to other extreme position and let the element come to rest.

(7) Read bubble positions.

If the adjustment is correct, the North-South level bubble will not move more than 5 divisions nor the East-West level bubble more than 1/4 inch. If, instep (4), the bubble in the East-West level moves toward the West, the knurled bell crank lever weight is too far out on the thread of the rod. Movement of the North-South bubble is controlled by a permanent weight under one end of the lever.

Each gyro unit is balanced at the factory about the vertical axis and also about the horizontal axis. Weights are fixed to the case to obtain these balances and to make the weight of each gyro unit the same as that of every other. This insures interchangeability of the units. These permanent weights should never be removed, or changed in any way.

• Gyro Wheel Balance

It sometimes happens that a gyro wheel requires rebalancing. This work should be attempted only where the necessary facilities are available and by one experienced in gyro wheel balancing.

When it is found that there is excessive vibration in a gyro wheel, the trouble is quite likely due to a defective bearing. The bearings should be replaced one at a time in accordance with the procedure outlined on page 117. After the bearings have been replaced and it is found that the wheel still will not run smoothly, the wheel may be rebalanced.

First the wheel must be put in a static balance, that is, it must be balanced while not running. This is absolutely essential, because no amount of adjusting will bring about a running, or dynamic, balance if the wheel is not in static balance.

Remove the balance hole cover and exhausting valve from the gyro case. Attach a suitable fitting in place of the upper spindle and suspend the unit from a firm support by means of heavy rubber bands of material similar to that used for gaskets between sections of repeater casings. Remove the centering spring stud and place a heavy bent wire in the stud hole to use as a handle by means of which the gyro case may be jiggled, so that it vibrates through a small angle about the gyro wheel bearings. Take off both bearing cover plates. Remove the spring from the case side and retainers from both sides. Shift the wheel axially to the center of its end play to free it from end thrust.

Place one of the balance holes in the wheel opposite the hole in the case and jiggle the case as explained above. If the wheel turns, rotate it through 180 degrees and repeat the operation. If it turns in the opposite direction this time, there is an unbalance. Remove one of the threaded balancing plugs from the heavy side of the wheel, take two or three strokes on the end of it with a file and replace. Try the balance again.

Repeat this operation until the wheel will stay perfectly still in any position in which it is placed when the case is vibrated about the wheel axis. A perfect static balance is essential to good running performance. Always keep the ends of the plugs rounded when filing them down, so that they will bear together on their axis of rotation when they are screwed together.

• Dynamic Balance

Dynamic balance is obtained by moving the balancing plugs axially in their threaded holes. After static balance has been obtained, suspend the gyro unit by means of a strong and securely fastened fitting from a firm support. Hang the unit as shown in Figure 73 by means of a stout rod so that it cannot come loose. The rod should extend up through a hole in its supporting member and be fitted with a metal washer and nuts at the top. Let the washer rest on several thicknesses of rubber. Do not hang the unit from a spring or rubber bands.

It is desirable to have some means for indicating vibration amplitude during the balance test runs. This means consists of a 1/4" diameter by 6" long rod suspended by threads as shown in Figure 73. Electric connection to the gyro unit must be made from a motor generator set through an ammeter for measuring the current in each phase. Adjust the motor generator speed control rheostat so that when the generator is started with the gyro connected, the gyro current will be 1 ampere. If the generator is run fast so that a heavier starting current is drawn, the frequent starting of the gyro during the adjustment will cause it to overheat.

To balance the wheel, turn on the motor generator and let the wheel slowly increase in speed. As the wheel speed increases, the vibration will also increase. Let the wheel pass through the first critical speed, noting, by the chatter of the rod and by feeling the wheel, the worst amplitude of vibration. Stop the wheel by means of two pieces of bakelite pressed against it through the balance holes in the casing and cover. Be sure to hold the bakelite pieces so that they will Press against the smooth side of the wheel and will not come in the Path of the threaded balancing plug holes. Do not stop the wheel by means of the motor generator, as this causes overheating when frequently repeated.

Start the wheel again and when, as closely as can be judged, the wheel is at the speed of the worst vibration as previously determined, make a mark on the side of the wheel with the pencil referred to above. The wheel should be touched very lightly through the balance hole in the casing side. Stop the wheel with the bakelite pieces and examine the mark made by the pencil. The length of the line is an indication of the unbalance of the wheel; a short line indicating a large unbalance and a long arc indicating a small unbalance. If the line is a short one directly above or very near one of the balance plug holes, move both plugs in that hole a short distance toward the side of the wheel on which the mark appears, remove the mark on the wheel, and repeat the procedure until the pencil traces a complete circle on the side of the wheel.

If the first marking leaves a short line between the two balance holes, move the plugs in both these balance holes toward the side of the wheel on which the mark appears. If the mark is nearer one hole, the plugs in that hole should be moved further than the plugs in the other. After moving the plugs, remove the mark on the wheel and repeat the procedure until the pencil leaves a complete circle on the side of the wheel.

Instead of moving a set of balance plugs in the hole nearest the mark, the same effect is obtained if the plugs in the hole diametrically opposite the mark are moved away from the side of the wheel on which the mark appears. This should be done when the plugs in the hole near the mark are near the side of the wheel.

The wheel is balanced when the pencil traces a circle and should run smoothly through both critical speeds. Continued vibration at higher speed, when the vibration at critical speed is not excessive, indicates a faulty bearing, or possibly a faulty stator or rotor.

If parts have been replaced before the wheel was balanced, the gyro unit should be subjected to a heat run in accordance with instructions on page 119.

• Electrical Zero of Commutator Transmitter

Both the single and 36-speed brushes are colored blue, red, and green in a clockwise direction. Three commutator segments, spaced 120° apart, are also colored blue, red, and green. The transmitter is on electrical zero when each brush rests on a segment of its own color. If the contact points of the single-speed blue brush rest in the center of the blue segment, then the red and the green brushes should be displaced from the segments of corresponding color by exactly 1/3 of the width of one segment and one insulating spacer away from the blue brush. The 36-speed brushes are adjusted in a similar manner except that the red and green brushes are displaced toward the blue brush. The outer brushes may be turned by loosening the three screws which clamp the single-speed brush assembly to the driving gear. The inner brushes may be adjusted by loosening the two hub clamp screws.

• Card Adjustment

When the brushes are on electrical zero the compass dials are set on zero. Remove the inner dial and loosen the screws which clamp the 36-speed dial to its hub. The dial may now be turned to its correct position. Replace the single-speed dial and adjust it before tightening its three clamping screws.

• Synchro Brush Dead Space

The synchro brush must have the correct lost motion between the follow-up head segments. This lost motion will be referred to as "dead space". If the dead space is too small, hunting may develop in the follow-up system; if it is too large, the lost motion introduces an appreciable error in the speed corrector. The correct dead space is 0.20 knots. It is measured as follows:

• Electrical Zero Setting on Synchro Motor

Unless the brush is correctly positioned upon the synchro shaft, the speed corrector mechanism will be out of step with the underwater log transmitter. The underwater log transmitter reads zero knots when its synchro generator is on electrical zero.

The procedure for checking and readjusting the electrical zero on the synchro motor is as follows:

If the electrical zero is incorrect, continue as follows:

• Gimbal System

With the sensitive element and spider completely assembled and in place, the gimbals are balanced so that the compass dials are level with respect to both fore and aft, and the athwartship axes. This is accomplished by adding a weight or weights to the inner gimbal ring. These weights are permanently attached and should not require changing at any time.

• Spring Damps

The 16 spring damps should all have about the same tension so as to keep the bowl centered in respect to the gimbal rings. A pressure of 18 to 20 ounces, measured at a point 1/8" above the sawcuts should hold the felts clear of the bowl. If no scale is available, remove the damps and check to see that the mounting ends of the new damps are bent at a 45-degree angle.

• Follow-up Coil

If there is a constant error in the settling point of the compass and the binnacle has been properly aligned, then the follow-up coil is displaced relative to the other parts of the follow-up mechanism. To correct this, loosen the three screws which clamp the follow-up coil to the stalk, turn the coil slightly, and reclamp. Repeat this operation until the settling point is correct.

• Ballistic Adjustment

The latitude dial on the control panel is calibrated to give a motor generator speed proportional to the cosine of latitude. To find the correct motor generator speed, apply the following formula:

M. G. Speed = 3000 (Cosine latitude setting).

Since the percentage of slip in the gyro motor is nearly constant, the gyro wheel speed is proportional to the cosine of latitude. The gyro wheel speed may be found by multiplying the motor generator speed by the number of pairs of poles in the generator and subtracting 3/5 of 1% from the result for slip. This generator has 6 pairs of poles. The gyro wheel speed is given by the formula:

Gyro Speed = (M.G. Speed) 6 - Slip

When it is desired to measure the gyro wheel speed more accurately, this maybe done by connecting a neon lamp. of the kind used on repeater panels, across one phase of the gyro supply. Hold the lamp close to the gyro sight glass. It will be observed that the spiral line appears to move across the wheel face. Each time the line passes, the wheel has slipped one revolution behind the synchronous speed. The exact value of slip will depend upon the degree of vacuum, the latitude setting, and other factors, but is usually between 1/2 of 1% and 1%.

• Follow-up System

On the follow-up panel is a sensitivity control which fixes the gain of the amplifier. The setting of this dial is not critical. If the sensitivity is too low, the torque produced by the follow-up motor for a given displacement of the dials will be low, or there may even be a small "dead space" within which the follow-up will not operate the dials. A high setting of the sensitivity control places an unnecessary load on the system. Ordinarily the adjustment is placed about half way between the upper and lower limits. When the 36-speed dial is displaced by hand, in either direction, the follow-up motor should return it to the same position with no appreciable dead space.

A milliammeter indicates the plate current of the 6A6 tube. Normally this current is about 1.5 to 2.5 milliamperes for a 115-volt, 1-phase supply.

If the follow-up system fails, look for shorts or loose connections. Check the follow-up circuit for voltage and resistance values. See pages 98 and 99 for normal values. The voltages were measured with the follow-up system synchronized, the card and the coil following the element at all times. 0heck the follow-up motor field and armature for possible burn-outs. An extra motor is included in the spare parts box.

• Follow-up Relay

When the follow-up coil is displaced from its normal position, the 6A6 tube is overloaded, causing the plate current to drop. The relay should be adjusted to operate when the current falls approximately 0.7 milliamperes below the normal value. This adjustment may be made by changing the spring tension. The contact points should be adjusted so that while the contact is open, there is a small space between the armature and magnet core to prevent sticking due to residual magnetism. When this contact is closed, the armature should be sufficiently close to the magnet to break the contact when the current returns to normal.

• Low-Voltage Relays

The low-voltage relays may be adjusted in the same manner as the follow-up relay. These relays should be set to operate when the voltage drops to about 80% of the full load voltage for the supply relay, and below 15 volts for the gyro supply relay.

• Repeater Cards

To check a repeater, put the commutator transmitter exactly on electrical zero. If the repeater is properly wired, the armature will take up a position such that a line on the shaft is opposite another line on the casing. The card should then read zero. To correct an error in the zero reading, loosen the nut which holds the card to the shaft and turn the card to zero. A special wrench for this purpose is included among the spare parts. The double dial bearing repeater is adjusted by loosening the screws which clamp the dial, and turning the latter to remove the error.

On the main commutator molding are three bronze slip rings with "L" shaped bronze brushes running on them. The pressure on each brush arm should be between 3 and 4 ounces. Adjustment may be made by bending the brush spring.

Three brushes, having equalized silver shoes, run on vertical bronze slip rings. Adjustment to a pressure of between 3 and 4 ounces may be made by bending the arms.

The single and 36-speed bronze brushes running on the commutator transmitter bars should have a pressure of between 6 and 7 ounces.

Keep commutator bars and slip rings clean and smooth. Clean with a rag moistened with alcohol. Apply the thinnest possible layer of Gulf Precision Grease No. 1 to the bars and slip rings. If it is necessary to smooth the commutator bars and slip rings, use a clean #6 file, never emery cloth. Clean parts thoroughly, being careful not to spill cleaning fluid on bearings or painted surfaces.

• Follow-up Coil Slip Ring Brush Adjustment

These five brushes each have four silver-tipped claws running on silver rings. Each brush has two arms, with two silver tips per arm. Each arm should have a pressure of between 1 and 1-1/2 ounces, measured at the silver tips. This pressure is extremely important. Too heavy a setting causes rapid wear on the silver slip rings; too light a pressure causes faulty contact.

• Damping Cut-out Contact Adjustment

The damping cut-out contacts should be set for approximately 15 degrees movement. Check as follows:

If the error is greater than 0.5 degree, proceed as follows:

PARTS REPLACEMENT

• General

When working on parts where there is a possibility of coming into contact with the sensitive element, it is advisable to stop the gyro wheels. Under no condition should parts be replaced on the sensitive element until the gyro wheels have been stopped. If instructions are followed, it will be found that in rare cases only will any adjustment of the sensitive element be necessary after repairs are completed.

Before disassembling any part of the compass, have boxes or other appropriate containers at hand so that the parts may be put in them as they are removed from the compass.

Make sure that the trouble has been properly located before proceeding with the work. See page 95 on "Troubles and Remedies", and page 101 on adjustments. Read the section on DESCRIPTION to become familiar with the construction of an assembly before attempting to dismantle it.

• Follow-up Motor Armature

• Follow-up Motor Field Coils

• Follow-up Coil

• Follow-up Magnet

• Disassembly of Transmitter

• To Remove the Spider Assembly

• To Replace the Spider Assembly

• Speed Receiver Synchro Motor Replacement

Should it be necessary to replace the speed receiver synchro motor, the following should be done after turning off the speed follow-up:

• Speed Follow-up Motor Replacement

• Disassembly of Compass Head

• To Remove Follow-up Coil Support and Stalk and Contact Tube

• Disassembly of Oscillator Mechanism

EXPLODED VIEW OF
OSCILLATOR MECHANISM
FIGURE 74

• Compass Lights

The two lamps which illuminate the compass binnacle are on the under side of the spider. They are 130 volt, 6 watt, candelabra base Mazda lamps. They are readily reached by removing the spider covers.

• To Remove Sensitive Element

• Float Ball Replacement

• To Remove a gyro Unit From the Sensitive Element

• To Replace a Gyro Wheel Bearing

• Gyro Unit Bearings

• To Evacuate the Gyro Casing

ARMA DWG NO 8178-203
VACUUM PUMP
FIGURE 75

After a gyro unit has been evacuated, it is desirable to run it at high speed and temperature for several hours in order to drive out moisture and also absorbed and occluded gases. This is best done by enclosing the unit in a wooden box having a close fitting door and a window through which the vacuum gauge may be observed. A heater in the bottom of the box dissipating about 400 watts will maintain the desired temperature. Mercury thermometers maybe inserted through small holes in the top of the box and joined to the case and cover by asbestos cement or other suitable material. See Figure 76. A motor generator set will, of course, be required for running the wheel.

• The Heat Run is Made as Follows:

(1) Place the evacuated unit in the box and attach a thermometer to each side as near the bearing as possible.

(2) Turn on the heater and bring the gyro wheel speed up to 18,000 R.P.M. See page 108, for measurement of wheel speed.

(3) Keep the temperature of the unit at 100° Centigrade. This may be adjusted by varying the heater voltage or by leaving the door open a little. A difference in reading of the two thermometers of more than five degrees indicates bearing trouble. If this should occur, remove the cover plate from the hotter bearing and make sure it is getting oil.

(4) After an hour or so the vacuum will probably drop an inch or two. The pump should then be connected and the case re-evacuated. This may be done while the wheel is running. Be sure to start pumping before vacuum valve is opened. Continue to evacuate the case from time to time until the pressure does not drop below 29 inches in twenty-four hours of running. Tighten up on the screws which hold the cover plates and flanges because the gaskets yield somewhat under the heat run.

(5) The proper oil level is approximately half way up the oil sight glass but this may vary a good deal. If the level is not correct after the heat run is well along, stop the wheel by reversing two of the leads. Observe the level. If the oil level is below 1/8 or above 3/4 of the way up the sight glass, add or drain gyro oil as required. Stopping the wheel by reversing the leads causes undesirable overheating and therefore should not be a common practice.

(6) If the rate of loss of vacuum does not decrease as the run progresses, stop the gyro by reversing two of the motor leads and replace any gaskets which have been changed during disassembly of the unit. Evacuate case and re-run at 18,000 R.P.M. for several hours, tightening up on screws until gasket has settled.

(7) When the wheel is stopped by reversing the motor leads, the motor windings rise to a high temperature. This usually results in a falling of the vacuum. If the gauge indication does not go below 28 inches and rises at least to 29 inches when the unit cools to room temperature, the unit is satisfactory and may be placed in service if it has passed the heat run.

In reading the vacuum gauge it is advisable to tap it lightly with a pencil. The exact reading will depend upon the barometric pressure. The values given above should be taken as approximations unless the gauge is checked and the readings corrected for atmospheric pressure changes.

• Follow-up Amplifier Unit

When trouble is encountered in the amplifier unit, Figure 56, it may be removed as a unit and replaced while being repaired. To replace the amplifier unit, disconnect all wires at the terminal block, remove tube and sensitivity control dial, and loosen the screws which fasten the amplifier box to the follow-up panel. The box may now be replaced.

SAFETY PRECAUTIONS

1. Compartment Pressure Test - Equalize pressure in all repeater compasses and gyro casings. See page 91.

2. When removing or handling the compass head (spider assembly) care must be observed to avoid straining the follow-up coil support and gearing. Never lift the spider by means of the follow-up coil arms. Except in emergency, the spider assembly should always be supported by blocks under the rim of the casting rather than by resting it on the follow-up coil support.

3. Never try to move the follow-up mechanism by pushing on the follow-up coil arms. The follow-up mechanism may be moved by turning the 36-speed dial with the thumbs. See Item 2, page 92.

4. When removing or replacing the compass head be careful not to damage the centering pin on contact prongs. See page 112.

5. Care should be observed when turning the sensitive element by hand, if the follow-up system is energized. Since the follow-up coil support follows every movement of the sensitive element, the operator's arm may be caught between the follow-up coil support and the spider frame.

6. Do not attempt any work on the sensitive element until the wheels have stopped turning. A serious accident may result. See page 111.

7. Care must be taken when connecting or disconnecting the wires from the gyro terminals. The nut under the cable lug should not be disturbed when the outer nut is turned. Failure to observe this precaution may break the seal and allow air to enter the case. No trouble will be experienced if the terminal lug is held in position while the outer nut is either loosened or tightened.

B. When testing the gyro unit for dynamic balance, it is imperative that the unit be suspended in such a manner that there is no possibility of it dropping through failure of a supporting member. Should the unit fall with the wheel turning at high speed, a serious accident would almost certainly follow. See page 104.

9. Do not stop the gyro wheels by means of reversing the motor generator leads. This causes undesirable overheating. See page 105.

10. Always close exhausting valve on gyro before stopping pump. If this precaution is not observed, oil from vacuum pump may be drawn into gyro casing.

11. When checking the electrical zero of a synchro motor, do not leave the power on for more than a few seconds at a time, or the synchro windings will overheat. See page 107.

12. Do not get cleaning fluids on any painted surfaces of the instrument.

13. Be very critical in making the slip-ring brush adjustments. Too heavy a setting causes unnecessary wear on the slip rings, and too light a pressure causes faulty contact. See page 109.

14. When disassembling the compass, take every precaution to protect the parts from collecting dust, grit, lint or other particles of matter. This may prevent further trouble. See pages 116, 117.

15. Do not turn the power supply switch to the "0n" position until the amplifier tubes have had a chance to warm up. See page 43.

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