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Section V
AN=08-10-112 Paragraph 32-34

small pinion gear This operaltion may result in an incorrect stop position. If so, the dial gear will have to be adjusted a tooth at a time until the correct position is reached. The hook on the roller arm should engage the stop on the tuning shaft as the index mark on the low frequency end of the 13.5-18.0 mc scale lines up with the frequency indicator of the index plate. However, the stop arm hook must not start to descend until the rotating stop has passed under tt on the last revolution of the tuning shaft.

d. STOP ARM RlEPLACENIENT.—Replacement of the stop arm may also require a readjustment to obtain the correct stop position. This is done by lengthening or shortening the roller end of the stop arm after loosening the two nuts on the arm.

e. REPLACENIENT OF DIAL AND MASK ASSEMBLY.—When the dial and mask assembly is replaced, the position of coupling 275 on the bracket and gear assembly and coupling 275 on the dial and mask assembly must be such that the position of the dial mask will correspond with the band switch position.

The correct relative positions are obtained when the mask is set to the 200-soo kc position and when coupling link 164 (see Fi,gure 16), connecting the band switch drive mechanism to tne band switch, is in a nearly vertical position, even with the front of the output transformer and filter choke unit 155.

f. DIAL CALIBRATION.—Correct dial calibration may be obtained after replacing a dial and mask assembly by adjusting the relation between the dial and tuning capacitor. To do this, loosen the two set screws in pinion gear and bushing assembly 268 until the gear will rotate freely on the shaft. Turn the tuning condenser until it is completely closed (rotor plates meshed with stator plates). Set the band switch for the 13.5-18.0 mc band. Turn the tuning knob until the isolated index mark at the low frequency end of the dial scale is alisned with the freqllency indicator on the index plate. Tighten the two set screws in the pinion gear and bushing assembly 268 carefully in order to avoid changing the position of the tuning capacitor, and apply glyptal to the heads of the set screws.

33. REMOVAL OF ANTENNA, R.F.
DETECTOR. AND OSCILLATOR UNITS

a. When the removal of the top or botsom cover plate does not give sufficient access to the antenna, r-f, or detector units, or when the oscillator ur.it is serviced, the entire assembly must be removed. this may be accomplished by repeating the following steps in the order given:

 

(I) Unsolder the leads at the front of the unit.

(2) With the rear of the recciver towards the repairman, remove top covers 225 on the unit to be serviced and the adjacent unit at the left.

(3) Set the band switch control to the b.5-6.0 mc band.

(4) One end of each retaining spring IGS is hooked over the band switch arm nearest the front of the chassis. Use long nose pliers and lift the ends of the two springs off the arrns (for the antenna unit only one spring must be removed). Also lift coupling links 161 oner the ends of the arms.

(5) Remove the tie strips on the top of the cans, front 229 and rear 227.

(6) Remove the screws fastening the bottom tie strips 227 and 228 to the unit to be removed.

(7) Remove .he mountinS screws at the front and rear of the unit

(8) Carefully lift the unit from the chassis.

b. To replace a unit, reverse the procedure givea above. Do not tighten the screws fastening the unit until after the band switch sections have been reconnected and the band switch operated a few times. Ihis will allow the unit to reposition itself.

34. TROUBLE LOCATION AND REMEDY.

a. QUICK CHECK.—Most service men, given a faulty receiver to repair, will seek a clue which will result in a rapid location of the trouble. If the user can be questioned, a helpful answer is often obtained.

A careful visual and mechanical inspection of the chassis and connections is generally one of the first steps Pulling at the various parts, including resistors, capacitors, wires and solder connections, will often locate a faulty connection.

Inspect parts and wiring for grounds or shorted connections and opcn circuits. Inspect resistors and coils for charred surfaces or discolorations that indicate an excessive current condition. The odor of ovcrheated insulation often tells the story of overload carried By the conductor.

If nothing is disclosed by the visual and mechanical inspection of the chassis and connections, the tubes may next be checked, since they are often the cause of the faulty operation. This may be done with n tube checker or by replacement with known good tubes

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