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1、HF/VHF TRANSCEIVER i746PRO SERVICE MANUAL INTRODUCTION This service manual describes the latest service information for the IC-746PRO HF/VHF TRANSCEIVER. DANGER NEVER connect the transceiver to an AC outlet or to a DC power supply that uses more than 16 V. This will ruin the transceiver. DO NOT expo

2、se the transceiver to rain, snow or any liquids. DO NOT reverse the polarities of the power supply when connecting the transceiver. DO NOT apply an RF signal of more than 20 dBm (100 mW) to the antenna connector. This could damage the transceiv- ers front end. ORDERING PARTS Be sure to include the f

3、ollowing four points when ordering replacement parts: 1. 10-digit order numbers 2. Component part number and name 3. Equipment model name and unit name 4. Quantity required 1110003870S.ICNJM2058M-T1IC-746PRO MAIN UNIT5 pieces 8810005770 Screw BiH M3 8 ZKIC-746PRO Top cover10 pieces Addresses are pro

4、vided on the inside back cover for your convenience. REPAIR NOTES 1. Make sure a problem is internal before disassembling the transceiver. 2. DO NOT open the transceiver until the transceiver is disconnected from its power source. 3. DO NOT force any of the variable components. Turn them slowly and

5、smoothly. 4. DO NOT short any circuits or electronic parts. An insu- lated tuning tool MUST be used for all adjustments. 5. DO NOT keep power ON for a long time when the trans- ceiver is defective. 6. DO NOT transmit power into a signal generator or a sweep generator. 7. ALWAYS connect a 50 dB to 60

6、 dB attenuator between the transceiver and a deviation meter or spectrum ana- lyzer when using such test equipment. 8. READ the instructions of test equipment thoroughly before connecting equipment to the transceiver. To upgrade quality, any electrical or mechanical parts and internal circuits are s

7、ubject to change without notice or obligation. TABLE OF CONTENTS SECTION 1SPECIFICATIONS SECTION 2INSIDE VIEWS SECTION 3DISASSEMBLY AND OPTION INSTALLATIONS SECTION 4CIRCUIT DESCRIPTION 4 - 1RECEIVER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8、 . . . . . . . . . . . . . . 4 - 1 4 - 2TRANSMITTER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 - 4 4 - 3PLL CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9、. . . . . . . . . . . . . . 4 - 6 4 - 4ANTENNA TUNER CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 7 4 - 5POWER SUPPLY CIRCUITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10、 . . . . . . 4 - 8 SECTION 5ADJUSTMENT PROCEDURES 5 - 1PREPARATION BEFORE SERVICING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 1 5 - 2PLL ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11、 . . . . . . . . . . . . . 5 - 2 5 - 3TRANSMITTER ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 4 5 - 4RECEIVER ADJUSTMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

12、. . . . 5 - 8 5 - 5ADJUSTMENT MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 10 SECTION 6PARTS LIST SECTION 7MECHANICAL PARTS SECTION 8SEMI-CONDUCTOR INFORMATION SECTION 9BOARD LAYOUTS 9 - 1S-LOGIC BOARD . . . . . . . .

13、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 1 9 - 2DISPLAY BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 3 9 - 3TEN-KEY BOARD . . . . . . .

14、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5 9 - 4MODE BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5 9 - 5PHONE BOARD . . . . . . .

15、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5 9 - 6RIT BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5 9 - 7PBT BOARD . . . .

16、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 5 9 - 8MIC BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 6 9 - 9MAIN UN

17、IT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 7 9 - 10 DSP UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

18、 - 9 9 - 11 RF UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 11 9 - 12 CTRL UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19、. . . . . . . . 9 - 13 9 - 13 TUNER UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 15 9 - 14 PA UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20、 . . . . . . . . . . . . . . . . 9 - 17 9 - 15 FILTER UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 19 9 - 16 DRV BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21、 . . . . . . . . . . . . . . . . . . . . . . . 9 - 19 9 - 17 VARISTOR-A BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 19 9 - 18 VARISTOR-B BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22、 . . . . . . . . . . . . . . . . . . . . . . 9 - 19 9 - 19 VARISTOR-C BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 - 19 9 - 20 VARISTOR-D BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23、 . . . . . . . . . . . . . . . . . . . . . 9 - 19 SECTION 10BLOCK DIAGRAM SECTION 11WIRING DIAGRAM SECTION 12VOLTAGE DIAGRAMS 12 - 1 DSP UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 1 12 - 2 FRONT UN

24、IT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 2 12 - 3 MAIN UNIT (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 3

25、12 - 4 MAIN UNIT (2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 4 12 - 5 PA UNIT, FILTER, DRV AND VARISTOR BOARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 5 12 - 6 CTRL A

26、ND TUNER UNITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 6 12 - 7 RF UNIT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 7 SECTION

27、1SPECIFICATIONS 1 - 1 I GENERAL Frequency coverage: Receive0.030 60.000 MHz*1, *2 108.000174.000 MHz*1, *2 Transmit1.8001.999 MHz*23.500 3.999 MHz*2 7.0007.300 MHz*210.10010.150 MHz*2 14.000 14.350 MHz*218.06818.168 MHz*2 21.000 21.450 MHz*224.89024.990 MHz*2 28.000 29.700 MHz*250.00054.000 MHz*2 14

28、4.000148.000 MHz*2 *1Except for some frequency ranges. *2Depending on version. Mode: USB, LSB, CW, RTTY, AM, FM Number of memory channels: 101 (99 regular, 1 call, 2 scan edges) Antenna connector : SO-239 3 (2 for HF/50 MHz bands and 1 for 144 MHz band; 50 ) Usable temp. range: 10C to +60C (14F to 1

29、40F) Frequency stability : Less than 7 ppm from 1 min. to 60 min. after power ON. After that the rate of stability change is less than 1 ppm at 25C (+77F). Temperature fluctuations (0C to +50C; 32F to 122F) less than 5 ppm. Freq. resolution: 1 Hz Power supply requirement: 13.8 V DC 15 % (negative gr

30、ound) Current consumption: Transmitmax. power23.0 A Receivestand-by2.2 A max. audio3.0 A Dimensions: 287(W) 120(H) 316.5(D) mm 11516(W) 42332(H) 121532(D) in Weight: 9.0 kg (19 lb 13 oz) ACC 1 connector: 8-pin DIN connector ACC 2 connector: 7-pin DIN connector REMOTE connector: 2-conductor 3.5(d) mm

31、 (18) I TRANSMITTER Output power: SSB/CW/RTTY/FM5100 W AM540 W Modulation system : SSBPSN modulation AMLow power modulation FMPhase modulation Spurious emission : Less than 50 dB (HF bands) Less than 60 dB (50/144 MHz bands) Carrier suppression: More than 40 dB Unwanted sideband suppression: More th

32、an 55 dB TX variable range : 9.99 kHz Mic. connector: 8-pin connector (600 ) ELE-KEY connector: 3-conductor 6.35(d) mm (14) KEY connector: 3-conductor 6.35(d) mm (14) SEND connector: Phono (RCA) ALC connector: Phono (RCA) I RECEIVER Receive system: Triple-conversion superheterodyne Intermediate freq

33、uencies: 1st IF freq.64.455 MHz 2nd IF freq.455 kHz 3rd IF freq.36 kHz Sensitivity (typical) : SSB, CW, RTTY (10 dB S/N) 1.829.99000 MHz*10.16 V 50.054.0000 MHz*20.13 V 144.0148.0000 MHz*30.11 V AM (10 dB S/N) 0.51.799999 MHz13 V 1.829.99000 MHz*12.0 V 50.054.0000 MHz*21.0 V 144.0148.0000 MHz*31.0 V

34、 FM (12 dB SINAD) 28.029.9900 MHz*10.5 V 50.054.0000 MHz*20.25 V 144.0148.0000 MHz*30.18 V *1Pre-amp 1 ON *2Pre-amp 2 ON *3Pre-amp ON Squelch sensitivity (Pre-amp OFF): SSB/CW/RTTY Less than 5.6 V FMLess than 1.0 V Selectivity (typical) : SSB (at 2.4 kHz bandwidth) More than 2.4 kHz/6 dB Less than 3

35、.2 kHz/40 dB Less than 3.6 kHz/60 dB Less than 4.3 kHz/80 dB CW (at 500 Hz bandwidth) More than 500 Hz/6 dB Less than 700 Hz/60 dB RTTY (at 350 Hz bandwidth) More than 360 Hz/6 dB Less than 650 Hz/60 dB AM (at 6 kHz bandwidth) More than 6.0 kHz/6 dB Less than 15.0 kHz/60 dB FM (at 15 kHz bandwidth)

36、More than 12 kHz/6 dB Less than 20 kHz/60 dB Spurious and image rejection ratio: More than 70 dB (HF/50 MHz band) (except IF through in 50 MHz band) More than 60 dB (144 MHz band) RIT variable range : 9.99 kHz Audio output power (at 13.8 V): More than 2.0 W at 10 % distortion with an 8 load PHONES c

37、onnector: 3-conductor 6.35 (d) mm (14) EXT SP connector : 2-conductor 3.5 (d) mm (18) 8 All stated specifications are subject to change without notice or obligation. SECTION 2INSIDE VIEWS 2 - 1 * Located under side of the point 1st LO PLL circuit PLL IC (IC1801: MC145170) 2nd LO and reference oscill

38、ator circuit 1st mixer circuit (Q211, Q212: 2SK1740) 3rd LO PLL circuit 2nd mixer (D261: HSB88WS) RF unit TX 3rd mixer (IC400: MC1496V) DSP unit RX 3rd mixer * (IC280: TC4W53F) MAIN unit MAIN AND RF UNITS 2 - 2 FILTER unit PA unit HF/50 MHz power amplifiers (Q5, Q6: 2SC2694) 144 MHz power amplifiers

39、 Q201, Q202: 2SC2694 ( CTRL unit SWR detector 8bit CPU (IC5: M38022M2) PA AND CTRL UNITS SECTION 3DISASSEMBLY AND OPTION INSTALLATIONS 3 - 1 Opening the transceivers case Follow the case and cover opening procedures shown here when you want to install an optional unit or adjust the internal units, e

40、tc. CAUTION: DISCONNECT the DC power cable from the transceiver before performing any work on the transceiver. Otherwise, there is danger of electric shock and/or equip- ment damage. q Remove the 2 screws from the left side of the transceiver to remove the carrying handle as shown at right. w Remove

41、 the 6 screws from the top of the transceiver and the 6 screws from the sides, then lift up the top cover. e Turn the transceiver upside down. r Remove 6 screws from the bottom of the transceiver, then lift up the bottom cover. UT-102 VOICE SYNTHESIZER UNIT The UT-102 announces the accessed readouts

42、 frequency, mode, etc. (S-meter level can also be announced) in a clear, electronically-generated voice, in English (or Japanese). Push LOCK/SPCH for 1 sec. to announce the frequency, etc. q Remove the top and bottom covers as shown above. w Remove the protective paper attached to the bottom of the

43、UT-102 to expose the adhesive strip. e Plug UT-102 into J1920 on the MAIN unit as shown in the diagram at right. r Adjust the trimmer, SPCH LVL: R1925 on the MAIN unit, to set the speech level if desired. Refer to the illustration at right. t Return the top and bottom covers to their original positi

44、ons. MAIN unit UT-102 J1920 R1925 3 - 2 CR-338 HIGH STABILITY CRYSTAL UNIT By installing the CR-338, the total frequency stability of the transceiver will be improved. q Remove the bottom cover as shown on the previous page. w Remove the 4 screws from the shield cover of the RF unit, and disconnect

45、P2 (CHASSIS) from J761 (MAIN unit), then lift up the shield cover. There is an earth spring on the shield cover, so be careful not to lose it when removing the cover. e Remove the 8 screws from the RF unit, disconnect J1, J121 and J151, then remove the RF unit. r Remove the supplied internal crystal

46、 and replace with the CR-338. t Return the RF unit, J1, J121 and J151 to their original posi- tions. y Connect a frequency counter to the J262, 2LO IN, then ad- just the reference frequency to be 64.00000 MHz with the L1901 on the RF unit. u Return the J262, shield cover, earth spring and bottom cov

47、- ers to their original positions. Earth spring Shield cover RF unit J761 (MAIN unit) P2 (CHASSIS) TUNER (antenna tuner) connector Black belt Blue belt J151 Blue J1 Black J121 Red CR-338 Supplied crystal Red belt RF unit Soldering points Connect a frequency counter, then adjust the frequency to be 6

48、4.00000 MHz. RF unit J262 2LO IN L1901 SECTION 4CIRCUIT DESCRIPTION 4 - 1 4-1 RECEIVER CIRCUITS 4-1-1 RF SWITCHING CIRCUIT (CTRL, RF AND PA UNITS) The RF switching circuit leads receive signals to bandpass filters from an antenna connector while receiving. However, the circuit leads the signal from

49、the RF power amplifier to the antenna connector while transmitting. RF signals (on HF/6 m bands) from ANT 1 or ANT 2 pass through the antenna selector (CTRL unit; RL3), tuner switch- ing relays (CTRL unit; RL1, RL2), transmit/receive switching relay (CTRL unit; RL4), and low-pass filter (CTRL unit; L27, L28, L35, C63C67, C105, C115C117), and are then ap- plied to the RF unit via J2 (P2). The signals from the CTRL unit bypass or pass through the 20 dB attenuator (RF unit; RL1, R1, R2). By selecting the at- tenuator, 0 (bypass) and 20 dB a