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Section V
AN=08-10-112 Paragraph 34

This can be done hy coupling a 915 kc signal through a 1 mf. capacitor to the control grid of the 1st detector. Short the stator of the oscillator section of the tuning c apacitor (Section 1-D) to ground. The output should go up. This indicates that the oscillator was functioning statisfactorily. Do lhis on all bands.

(12) R-F AMPLFIER AND HETERODYNE OSCILLATOR.— Having completed the test and alignment of the audio amplifier, i-f amplifier and heterodyne oscillator, test the r-f amplifier as follows:

Turn the band switch to band No. 1. Set the receiver and generator controls as described in Table G Alignment Chart, No. I band column, but use a .l mf. dummy antenna and make the antenna connection to the control g rid of the 1st detector tube.

Turn the tuning controI until the test signal is picked up and carefully tuned in. The receiver dial should indicate the same frequency as the signal generator. If there is more than .75 per cent variation, the oscillator must be realigned as described beIow

Proceed to check the r-f amplifier, stage-by-stage, working towards the antenna. Couple the signal generator through the .1 mf. dummy antenna to the control grids of the 2nd r-f tube and the 1st r-f tube. Then, using a dummy antenna of 100 mmf, couple the signal generator to the antenna binding post. At each stage, the receiver output should incrcase substantially indicating the stage gain. If there is no gain, the stage should be checked for defective components, shorts and grounds, using Tables C, D and E.

Do this on all bands.

(13) R-F AMPLIFIER AND HETERODYNE OSC:I.LATOR ALIGNMENT.—Instructions are given in Table G Alignment Chart for completely aligning the r-f amplifier and heterodyne oscillator circuits. Start with number 1 band column and continue with all columns to the right.

f. WEAK OR NO SlGNALS ON ANY ONE BAND, MOdULATED RECEPTION.—The condition of satisfactory reception on several bands and weak or no signals on one or more bands indicates the correct functioning of the i-f and a-f amplifiers, and requires checking only the r-f amplifier and heterodyne oscillator for the defective band or bands. The procedure outlined in paragraphs 34e(11) to 34e(13) should be followed for the defective band or bands.

8 WEAK OR NO SIGNALS ON ALL BANDS— C • W RECEPTION MODULATED RECEPTION NORMAL)—Weak or no signals on all bands for c-w reception with satisfactory modulated signal reception,


requires testing and alignment of tbe c-w oscillator. Proceed as outlined in Paragraphs 34e(9) and 34e(10).

b. MEASUREMENTS WlTH TEST SET 1-56-A.— The tables that follow show voltage and resistance measuremcnts made from the chassis ground to the tube socket terminals and other important points. These measurements were made with Model 665 Analyzer and other equipment contained in Test Set 1-56-A. They are typical readings that will be approximated in Signal Corps Repair Shops when using this equipment on receivers in good operating condition. When faulty operation of Radio Receiver BC.348-(*) is encountered, see that all plugs are firmly seated and check carefully the cables and plugs with Model 564 Voltohmmeter as instructed on page 11 of the instruction book for Test Set 1-56-A under “Detailed Tests on Radio Sets” If the trouble is not located in the cables, remove the chassis and check the tubes with Model 685 Tube Tester as instructed on page 11 of the test set instructions. After this is done, proceed with the voltage and continuity measurements described below:

(l) VOLTAGE AND CURRENT MEASUREMENTS.—Instructions are given on page 12 of the test set insiruction book for making voltage and current measurements with Model 665 Analyzer and Model 666 Socket Seleaor. Latest instructions which include the use of the octal socket adapter are necessary. These instructions should be follo wed for measurements on all except the second r-f tube

When making measurements at the second r-f tube, the flexible lead on the orange adapter plug must be removed from the pin jack marked GND and inserted in the outer No. X 3 jack, as the shield is not grounded.

Great care must be exercised when inserting the analyzer plug into the sockets on the r-f tube shelf in order to avoid damage to the prongs, as the shelf is mounted at an angle that just permits the insertion of the plug.

PROCEDURE 1. With the chassis removed from the cabinet and power supplied to the receiver through the connector plug, place the controls in the positions designated on the voltage table.

2. Set up the 665 Analyzer and the 666 Socket Selector for making readings on metal tubes as instructed on page 12 of the test set instructions. (See note above for second r-f tube setup.)

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