R-390A_user_TM11-856_1955.pdf

. 31: - - cI. . . . Q Co - - I N c: I - r ,. 5! co . !. < ,., i ., < - c: i - eatillg-of connector P119 (fig. 88). If neither output is affected, check tubes V507 and V601. If tube replacement is not effective, trouble shoot the af subchassis at a field maintenance level. b. IF Noise Test. Set the BANDWIDTH switch at 16 KC. With the other controls set for audible noise, set the BANDWIDTH switch successively at each lower position while listen- ing to the noise. The noise should decrease at each position, until it can hardly be heard in the .1 KC position. If there is little or no change in noise output as the switch is rotated, check tubes V501 through V504. If the tubes are not defective, further trouble shooting of the IF subchassis at a field maintenance level will be necessary. c. Noise at Grid Test Points. Set the multi- meter to the highest resistance range. Connect one 111ultimeter lead to the chassis and, in turn, touch the prod on the other lead to grid test points E210, E209, E20S, E207, and E206, in that order (fig. 62). A click should be heard each time the prod touches the test point. If no click is heard, check the tube closest to the check point. Be sure that all connectors are seated firmly in their receptacles. d. RF TuneJ Noise Test. Starting with the megacycle frequency indicator at 02, turn the MEGACYCLE CHANGE ,control through its range to the highest frequency, while listening to the noise in the headset or loudspeaker. There should be a sharp and pronounced increase in noise as the control is seated in each detent position. Across the tuning range, some adjust- ment of the ANT TRIM control will be neces- sary to produce maximum noise. Between de- tent settings, the noise should show a pro- nounced drop in level. From one detent to the next (except between the settings where RF coil ranges are to be switched), the noise level should be almost constant. RF coils are switched behveen the following settings: 03 and 04, 07 and OS, 15 and 16. If noise at any point across the range is not maximum with the knob in the detent position, mistracking at that point is possible. Adjustment at a field maintenance level is required. The RF and variable IF aline- rnent should be checked (pars. 114, 115, and 116). If the noise does not drop between detent settings, check for excessive IF gain (par. l1S). If noise is less at one detent setting, check the AGO 3250A over-all gain (par. 117.1) and the adjustment of the crystal-oscillator trimmer capacitors (pars. 112 and 113). c. Antenna Circuit Noise Tests. Rotate the ANT TRIM control. The noise should peak at one particular point. Ground the center contact of the ANTENNA UNBALANCED WHIP connector JI07. A click should be heard and the noise should drop sharply. Ground both con- tadts of the BALANCED 125 OHM connector JI08. A click should be heard and the noise drop sharply. If the receiver does not pass these tests, check the antenna relay, the connectors on the antenna relay box, and the sections of the RF band change switch that connect to transform- ers 1201 through T206. Page 35, paragraph 43b (2). Add the follow- ing after the last sentence: If the output of the calibration oscillator is unstable or there is frequent tube failure, change the 12AU7 tubes to type 5814A tubes. Page 40, paragraph 47. Normal indications column, line 34. Change of to: af. Page 46, figure 30. Add a ground symbol to cathode resistor R404. Delete the connection drawn between the ground end of R404 and jack J421. Page 47, paragraph 55, line 5. Change 36- mc to: 32-mc. Page 48, figure 32. Add a ground symbol to cathode resistor R408. Face page 84, figure 61. Add reference sym- bols to the AMPHENOL connectors as shown in the following chart: Cable No. AM PHENOL Ref symbol 8 26-806 J517 8 26-807 P1l7 3 26-150 Pl19 3 26-151 J619 4 26-804 J620 4 26-805 P120 5 26-150 Pl18 5 26-151 J818 6 26-192 Pl13 6 26-1059 J413 26-1059 P715 26-192 J115 2 26-192 P114 2 26-1059 J214 AGO 3250A Page /is, paragraph 02, Correction colun!, line 10. Add the following after line 10: Substi- tute tube type 5814A for defective tube type 12AU7 in V901 and V902. Page 90, figure 63. Delete reference symbol J323 and substitute: J223. Page 90, figure 64. Delete reference symbol S208 (next to S210) and substitute: S209. Page 107, paragraph 105e (1). Add the fol- lowing to subparagraph (1) : In early production models of the receiver the green-coded offset gear is merely reversed to mesh with the gear train. Page 108, paragraph 105d. (10.1) (Added) Tighten the rear right green mounting screw. Subparagraph (13), line 1. Add the follow- ing after offset: gear. Subparagraph (13). Add the following: In early production models of the re- ceiver, the green-coded offset gear is reversed to disengage from the RF gear train. Page 112. 105.1. Disassembly of RF Gear Train Assembly (Added) a. General. Under certain circumstances, such as extensive damage or mechanical failure of a component, it may be necessary to disassemble all or part of the RF gear train assembly. The instructions given in this paragraph should be used as a guide when the method of removal of parts is not obvious. The index numbers used in the instructions refer to those that identify the parts in figure 88.1. When disassembling the RF gear train assembly, mark the individual gears with the index number. This will aid identification and reassembly. Place the parts in trays or containers in the order of disassem- bly. This will simplify reassembly. b. Disassembly. (1) Remove the front panel (par. 105a). (2) Remove the RF subchassis (par. 105c) . (3) Remove the 8 slug racks and the 16 tension springs. Tag the slug racks for identification according to frequency. 4 (4) Loosen the %6-inch hexagonal nut (1) and %6-inch lock washer (2) and re- move the 6-32 by %6-inch Phillips head screw (3) and the No. 6 lock- washer (4). Remove the clutch gear assembly. Remove the o/t6-inch hexag- onal nut (1) and %6-inch lockwasher (2). To disassemble the clutch gear assembly, follow the procedures in (a) and (b) below. If it is not necessary to disassemble the clutch gear, pro- ceed with (5) below. (a) Remove the .395-inch retaining ring (5), split gear assembly (6), YI6-inch flat washer (7), four 1%2- inch spring friction washers (8), two YI6-inch flat washers (9), steel plate (10), four clutch plates (11), and brass gear (12). (b) Remove the zero adjust shaft (13), the .225-inch retaining ring (14), stop washer (15), spring holder (16), stop spring (17), flat pin (18), 1,4-inch washer (19), .225- inch retaining ring (20), steel bush- ing (21), from the clutch assembly shaft (22). (5) Remove the four 4-40 by %6-inch Phillips head screws (23) and four No. 4 split lockwashers (24) to re move the mechanical counter (25). (6) Remove the beveled gear (26) and gear clamp (27) by loosening the 3-56 by 1,4-inch Bristo head screw (28). (7) Remove the beveled gear (29) and gear clamp (30) by loosening the 3-5f by lJ:t,-inch Bristo head screw (31). (8) Remove the two beveled gear assem- blies (32) and (33). (9) Remove the 6-32 by l7i6-inch Phillips head screw (34) and No. 610ckwasher (35) and green-faced gear (36). (10) Remove the .207-inch retaining ring (37) and the brass gear (38). (11) Remove the .207-inch retaining ring (39) and remove the hollow pin (40) from brass gear ( 41). Pull out the gear and shaft assembly (42) while sliding off gear (41) and l7i6-inch washer (43). (12) Hemove the 6-40 by o/,c-inch machine screw (44). (13) Remove the front plate assembly (45) by removing the three 8-32 by % c- inch Phillips head screws (46) and the three No.8 lockwashers (47). (14) Remove the .225-inch retaining ring ( 48) and pull out the welded gear and shaft assembly (49) from the rear of the front plate assembly (45). (15) Remove the .122-inch retaining ring (50) to remove the large brass gear (51) . (16) Remove the three 6- 32 by lA-inch Phillips head screws (52) and the three No. 6lockwashers (53) that hold the triangular steel plate (54) to the front plate assembly (45). (17) Remove the .122-inch retaining ring (55) and remove the pinned gear assembly (56) and o/J Ii -inch washer (57) . (18) Remove the two 6- 32 by 1j4-inch Phil- lips head screws (58) and the two No. 610ckwashers (59) holding the detent spring (60). (19) Remove the differential gear assem- bly (61) through (72). To disassem- ble the differential gear assembly, fol- low the procedures given in (a) through (e) below. If it is not neces- sary to disassemble the differential gear, proceed with (20) below. (a) Remove the three 4-40 by i;4.-inch Phillips head screws (61) and the three No.4 lockwashers (62). I (b) Gently lift off the pinned gear as- sembly (63). (c) Remove the three .122-inch retain- ing rings (64) and remove the three identical brass split gear assemblies (65) . Nate. The third brass gear assembly is shown exploded with index numbers (66) through (69) in figure 88.1. (d) Remove the .395-inch retaining ring (66) and separate the flat brass gear (67), the steel loading spring (68), and the pinned brass and steel gear assembly (69). AGO 3260A (e) Remove the .395-inch retaining ring (70) to facilitate the removal of loading springs (71) on pinned gear and detent assembly (72). (20) Remove the pinned split gear assem- bly (73) and %6-inch washer (74). (21) Remove the steel split gear assembly (76) through (79), %6-inch steel washer (75) and dismantle by remov- ing the %6-inch retaining ring (76) that separates steel gear (77), sepa- rator (78), and steel gear (79). (22) Remove the .281-inch retaining ring (80) to remove the large brass gear assembly (81). (23) Remove the large brass gear (82) by loosening the 4- 40 by %6-inch Bristo head screw (83) and the 4-40 square nut (84) on gear clamp (85). (24) Remove the small steel gear (86) by loosening the 4- 40 by %6-inch Bristo head screw (87) and the 4-40 square nut (88) on gear clamp (89). (25) Remove the .122-inch retaining ring (90) to remove the brass gear (91). (26) Loosen the 4-40 by %6-inch Bristo head screw (92) and the 4- 40 square nut (93) on the gear clamp (94) to remove the steel gear (95) and the steel split gears (96). To disassemble the split gears, remove the three 4-40 by 14-inch Phillips head screws (97). (27) Loosen the 4-40 by %6-inch Bristo head screw (98) and the 4-40 square nut (99) on the gear clamp (100) to remove the steel gear (101) and the steel split gear (102). (28) Loosen the 4-40 by %6-inch Bristo head screw (103) and the 4-40 square nut (104) on the gear clamp (105) to remove the steel split gear (106) . (29) Loosen the 4-40 by %6-inch Bristo head screw (107) and the 4-40 square nut (108) on the gear clamp (109) to remove the split gear (110) and the the small steel gear (111). (30) Remove the three 4-40 by lAt.-inch Phillips head screws (112) to remove the split gear assembly (113). GO 3250A (31) Remove the No. 6/0 taper pin (114) to remove the cam (115). Pull the shaft (116) out through the front of the RF subchassis and remove the cam and gear assembly (117) by re- moving the No.6 taper pin (118). (32) Loosen the 4-40 by %6-inch Bristo head screw (119) and the 4- 40 square nut (120) on the gear clamp (121) to remove the split gear (122). (33) Loosen the 4- 40 by %6-inch Bristo head screw (123) and the 4- 40 square nut (124) on the gear clamp (125) to remove the split gear (126). (34) Remove the 8-32 by %6-inch Phillips head screw (127) and the No.8 lock- washer (128) to remove the Geneva system and overtravel coupler. Sepa- rate the gear assembly by removing the steel plate (129), steel ball (130), and 10-tooth lost motion gear (131). Remove the .122-inch retaining ring (132) and washer (133) to separate the brass gear (134) and shaft (135). (35) Remove the 6- 32 hexagonal nut (136) and No.6 lockwasher (137). Remove the 1b-inch retaining ring (138) and separate the steel eight-tooth and four- tooth gear (139) and the shaft (140) from the rear plate (146). (36) Remove the 6- 32 by %6-inch hexag- onal head screw (141) and the No.6 lockwasher (142). Remove the .122- inch retaining ring (143) and sepa- rate the brass gear (144) and steel shaft (145) from the rear plate (146). (37) Remove the .225-inch retaining ring (147). Loosen the 4- 40 by %6-inch Bristo head screw (148) and 4-40 square nut (149) to loosen the gear clamp (150). Separate the shaft (151) from the gear (152). (38) Remove the two 6- 32 by %6-inch Phillips head screws (153) and No. 6 lockwashers (154) to loosen the flange (155). Remove the shaft and gear assembly (156). Remove the hollow pin (157) to separate the Oldham cou- pler (158), flange (155), and %6-inch washer (159) froU the shaft and gear assembly (156). 5 6 (39) Remove the No. 6/0 taper pin (160) and the cam (161). Hemove the No. f taper pins (162) and (164) to 100se11 the cams (163) and (165 , Remove the cam shaft (166). Remove the No, 6/0 taper pin (167 ana. the can: 168) . (40) Remove the No. 6/C taper pin (169; and the cam (170) to remove the can: shaft (171. Remove tll.e No. 6/0 taper pin (172 and the cam (173). (41) Remove the No. G/G taper pin (J74 and the cam and gear assembly (175 to remove the cam sh.aft. (:i 76). He- move the No. G/O taper pir; (;77) am the cam (178). (42) Remove the No. 6/0 ta.per pin (179) and the cam (80)-to remove the can shaft (I8!. ReJllOVe the No. 6/0 tapel pin (182) and t1e call: OBa. (43) Remove the No. 6/0 taper pin (184) and the cam (185) to remove the cam shaft (l86). Remove the Nc. B/C taper pin (187) and the cam 188). (44) Remove the No. 6/0 taper pin (189) and the cam (190) to remove the cam shaft (191). Remove the No. 6/0 tape pin (192) and the cam (193). (45) Remove the No. 6/0 taper pin (194) and the cam (195) to remove the cam shaft (196). Remove the No. 6/0 taper pin (197) and the cam (198). (46) Loosen the four 8-32 by %2-inch Bristo head screws (199) and remove the %,-inch coupler (200) and the l/j,., inch fiber shaft (201). Remove the %-32 hexagonal head nut (202), o/a- inch lockwasher (203), o/a-inch fiat washer (204), and the o/a-inch fiber washer (205). (47) Remove the six 6-32 by iVa-inch Phillips head screws (206) and the six No.6 lockwashers (207) that hold the three brackets (208) and the three rods (209) to the rear plate (146). (48) Remove the three 8-32 by o/s-inch hexagonal head screws (210) and the three No.8 lockwashers (211). (,19) Remove the three 8-32 by %,-inch flat- head Phillips head screws (212) that hold the three separator rods (213). (50 Remove the. twc 8-32 by iVa-inch hexagona head screwiO (2H) and the two No.8 lockwashen! (215 0 Remove the 8-32 by l,4-iIiCb fl.atheac Phillipe head screw (Z1.6 and the No.8 lock- washer (21.7) to remove the BY iOub- chassis real plate (2.8. 105,2. Reassembty of rtF Gearlrafn Assembly (Addeo a. General. Use the inde.x number ir; figure 87.1 a a guide in reassembly. If there iiO any doubt aE