ICOM IC-706MKIIG Service Repair Manual

SERVICE MANUAL HF/VHF/UHF ALL MODE TRANSCEIVER i706MK™G Downloaded from www.Manualslib.com manuals search engine

INTRODUCTION This service manual describes the latest service information for the IC-706MKIIG HF/VHF/UHF ALL MODE TRANS- CEIVER at the time of publication. To upgrade quality, any electrical or mechanical parts and internal circuits are subject to change without notice or obligation. 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 expose 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 transceiver’s front end. ORDERING PARTS Be sure to include the following 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 <SAMPLE ORDER> 1110004080 S.IC μPC2709T IC-706MKIIG MAIN UNIT 05 pieces 8810009020 Screw FH M2.6 x 5 ZK IC-706MKIIG Top cover 10 pieces Addresses are provided 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 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 transceiver is defective. 6. DO NOT transmit power into a signal generator or a sweep generator. 7. ALWAYS connect a 50 dB to 60 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. VERSION NO. #02, #12 #03, #13 #04, #14 #05, #15 #08, #18 VERSION Europe France Spain U.S.A. Other SYMBOL EUR FRA ESP USA OTH Downloaded from www.Manualslib.com manuals search engine

TABLE OF CONTENTS SECTION 1 SPECIFICATIONS SECTION 2 INSIDE VIEWS SECTION 3 CIRCUIT DESCRIPTION 3 - 1 RECEIVER CIRCUITS ................................................................................................................................ 3 - 1 3 - 2 TRANSMITTER CIRCUITS......................................................................................................................... 3 - 4 3 - 3 PLL CIRCUITS ............................................................................................................................................ 3 - 6 3 - 4 LOGIC CIRCUITS ....................................................................................................................................... 3 - 8 SECTION 4 ADJUSTMENT PROCEDURES 4 - 1 PREPARATION BEFORE SERVICING ...................................................................................................... 4 - 1 4 - 2 PLL ADJUSTMENTS................................................................................................................................... 4 - 2 4 - 3 TRANSMITTER ADJUSTMENTS ............................................................................................................... 4 - 2 4 - 4 RECEIVER ADJUSTMENTS....................................................................................................................... 4 - 8 4 - 5 SET MODE ADJUSTMENT....................................................................................................................... 4 - 10 SECTION 5 PARTS LIST SECTION 6 MECHANICAL PARTS AND DISASSEMBLY SECTION 7 SEMI-CONDUCTOR INFORMATION SECTION 8 BOARD LAYOUTS 8 - 1 DISPLAY BOARD........................................................................................................................................ 8 - 1 8 - 2 MAIN BOARD.............................................................................................................................................. 8 - 3 8 - 3 HPF AND DRIVER BOARD ........................................................................................................................ 8 - 5 8 - 4 PA UNIT....................................................................................................................................................... 8 - 7 8 - 5 PLL UNIT..................................................................................................................................................... 8 - 9 8 - 6 FILTER BOARD......................................................................................................................................... 8 - 11 SECTION 9 BLOCK DIAGRAM SECTION 10 VOLTAGE DIAGRAM Downloaded from www.Manualslib.com manuals search engine

■ GENERAL • Frequency coverage : Receive 0.030 – 200.000 MHz* 430.000 – 470.000 MHz* Transmit 1.800 – 1.999 MHz* 3.500 – 3.999 MHz* 7.000 – 7.300 MHz* 10.100 – 10.150 MHz 14.000 – 14.350 MHz 18.068 – 18.168 MHz 21.000 – 21.450 MHz 24.890 – 24.990 MHz 28.000 – 29.700 MHz 50.000 – 54.000 MHz* 144.000 – 148.000 MHz* 430.000 – 450.000 MHz* *Depending on version. • Mode : USB, LSB, CW, RTTY (FSK), AM, FM, WFM (WFM is for receiver only) • Number of memory ch. : 107 (99 regular, 6 scan edges,1 call) • Antenna connector : SO-239 ✕ 2 (for HF/50 MHz and 144/440 MHz)/50 Ω • Power supply requirement : 13.8 V DC ±15% (negative ground) • Frequency stability : Less than ± 7 ppm from 1 min. to 60 min. after power ON. After that, rate of stability less than ±1 ppm/hr. at +25˚C (+77˚F). Temperature fluctuations 0˚C to +50˚C (+32˚F to +122˚F) less than ± 5 ppm. • Current consumption : Transmit max. power 20 A Receive standby 1.8 A max. audio 2.0 A • Usable temperature range : –10˚C to +60˚C (+14˚F to +140˚F) • Dimensions : 167(W) ✕ 58(H) ✕ 200(D) mm (projections not included) 6 9 ∕16(W) ✕ 2 9 ∕32(H) ✕ 7 7 ∕8(D) inch • Weight : 2.45 kg (5 lb 6 oz) • CI-V connector : 2-conductor 3.5 (d) mm ( 1 /8")/8 Ω • ACC connector : 13-pin ■ TRANSMITTER • Output power : 1.8–50 MHz band SSB/CW/RTTY/FM 5–100 W AM 2–40 W 144 MHz band SSB/CW/RTTY/FM 5–50 W AM 2–20 W 440 MHz band SSB/CW/RTTY/FM 2–20 W AM 2–8 W • Modulation system : SSB Balanced modulation AM Low level modulation FM Variable reactance modulation • Spurious emissions : Below 47.5 MHz Less than –50 dB (typical) Above 47.5 MHz Less than –60 dB • Carrier suppression : More than 40 dB • Unwanted sideband supp. : More than 50 dB • Microphone connector : 8-pin modular jack (600 Ω) • KEY connector : 3-conductor 6.35 (d) mm ( 1 /4") • RTTY connector : 3-conductor 3.5 (d) mm ( 1 /8") ■ RECEIVER • Receive system : SSB/CW/AM/WFM Double superheterodyne FM Triple superheterodyne • Intermediate frequencies : *FM or FM-N mode only • Receive sensitivity : (pre-amp ON) Note: SSB, CW and AM modes are measured at 10 dB S/N; FM mode at 12 dB SINAD. *Except 4–4.5 MHz, 8–9 MHz. • Squelch Sensitivity : (pre-amp ON) SSB Less than 5.6 μV FM Less than 0.32 μV • Selectivity* : SSB, CW, RTTY More than 2.4 kHz/–6 dB Less than 4.8 kHz/–60 dB AM/FM-N More than 8.0 kHz/–6 dB Less than 30 kHz/–40 dB FM More than 12 kHz/–6 dB Less than 30 kHz/–60 dB *Without an optional filter unit and with mid bandwidth selected. • Spurious and image rejection ratio: HF band 70dB 50 MHz band 65 dB (except IF through) 144/440 MHz band 65 dB • Audio output power : More than 2.0 W at 10% distortion (at 13.8 V DC) with an 8 Ω load • RIT variable range : ± 9.99 kHz • PHONES connector : 3-conductor 3.5 (d) mm ( 1 /8")/8 Ω • EXT SP connector : 2-conductor 3.5 (d) mm ( 1 /8")/8 Ω 3rd IF 455 kHz* 455 kHz* — — — MODE SSB/AM-N/FM AM/FM-N CW RTTY WFM 1st IF 69.0115 MHz 69.0100 MHz 69.0106 MHz 69.0105 MHz 70.7000 MHz 2nd IF 9.0115 MHz 9.0100 MHz 9.0106 MHz 9.0105 MHz 10.7000 MHz 1 - 1 SECTION 1 SPECIFICATIONS FM — — 0.5 μV 0.25 μV 0.18 μV 0.18 μV FREQUENCY 0.5 – 1.8 MHz 1.8 – 28 MHz* 28 – 29.999 MHz 50 MHz band 144 MHz band 440 MHz band SSB/CW/RTTY — 0.16 μV 0.16 μV 0.13 μV 0.11 μV 0.11 μV AM 13 μV 2 μV 2 μV 1 μV 1 μV 1 μV All stated specifications are subject to change without notice or obligation. Downloaded from www.Manualslib.com manuals search engine

Predrive amplifier (Q101: 2SK2854) HPF board D/A converter (IC2201: M62352GP) ¡PA AND PLL UNITS FILTER board MAIN CPU clock (X2161: CR-636) MAIN CPU * (IC 2001: HD6433337YA56F) MAIN board 3rd IF filter for FM * (FI791: SFPC455E-TC01) MIC amplifier (IC931: μPC5023GS-077-E1) AF selector switch * (IC861: BU4052BCFV-E2) Tx FM PLL IC * (IC1011: LC7153M-TLM) Balanced modulator * (IC1041: NJM1496V) Discriminator (X791: CDB455CX24) FM IF IC * (IC791: TA31136FN) RX preamplifier (IC151: μPC1658G) 1st mixer (D271: HSB88WSTR) 1st IF filter (FI511: FI-261) 2nd mixer * (D551: HSB88WSTR) 2nd IF filter (FI561: FL-23) Space for optional filters FL-100, FL-101, FL-103   FL-233, FL-232  Power amplifers (Q171, Q172, Q231: SRFJ7044) DDS IC (IC101: SC-1246) BFO DDS IC (IC901: SC-1287) PLL IC * (IC461: LMX2306TMX) VCO1 * (Q301: 2SK508) VCO2 * (Q331: 2SK508) PA unit DRIVER board Drive amplifers (Q161, Q211: MRF1508TI) Predrive amplifer (Q121: MXR9745) AF power amplifer (IC231: LA4425A) PLL unit AF volume controller (IC201: M5282FP) VCO3 * (Q361: 2SK508) Reference oscillator (X621: CR-275A 30.00000 MHz) *Located under side of the point ¡MAIN AND FILTER BOARDS 2 - 1 SECTION 2 INSIDE VIEWS Downloaded from www.Manualslib.com manuals search engine

3-1 RECEIVER CIRCUITS 3-1-1 HF/50 MHz RF CIRCUIT (FILTER, MAIN AND HPF BOARDS) HF/50 MHz RF filters pass only the desired band signals and suppress any undesired band signals. The HF/50 MHz RF circuit has 7 low-pass filters and 8 high-pass filters for specified band use. HF/50 MHz RF signals from the [ANT1] connector, pass through one of 7 low-pass filters as below, the transmit/ receive switching relay (FILTER board; RL1) and low-pass filter (FILTER board; L1, L2, C1–C5), and are then applied to the MAIN board via J1 (FILTER board). The signals from the FILTER board are applied to or bypass the 20 dB attenuator (R122, R125, R126). The signals pass through the high-pass filter (L132, L133, C132–C137) to suppress strong signals below 1.6 MHz and are then applied to the HPF board via the “SAF” terminal. (1) 0.03–2 MHz and 30–40 MHz The signals pass through a low-pass filter (L101, L102, C101–C105), and then applied to the preamplifier circuit on the MAIN board. (2) 2–30 MHz The signals from the low-pass filter (L101, L102, C101–C105) are applied to one of 6 high-pass filters as at right above and are then applied to the preamplifier circuit on the MAIN board. (3) 40–60 MHz The signals pass through the low-pass filter (L172, L173, C172–C176) and the high-pass filter (L174, L175, C177–C181) via D171 and are then applied to the preamplifier circuit on the MAIN board. 3-1-2 VHF AND UHF RF CIRCUITS (PA UNIT) The VHF and UHF RF circuits pass and amplify only the desired band signals and suppresses any undesired band signals. The both RF circuits have a preamplifier and bandpass filters respectively. • VHF RF CIRCUIT The VHF RF signals from the [ANT2] connector pass through the low-pass filter (L263–L265, C274–C276) and antenna switching circuit (D291–D293). The signals are applied to the bandpass filter (D403, D409, D408), and are then amplified at the preamplifier circuit (Q403). The amplified signals are then applied to the another bandpass filter (D407, D406, D410). • UHF RF CIRCUIT The UHF RF signals from the [ANT2] connector pass through the high-pass filter (L316, L317, C326–C327), low- pass filter (L313–L315, C322–C324) and antenna switching circuit (D341, D342, D343). The signals are amplified at the preamplifier circuit (Q453) between the 2 bandpass filters (D454, D453 and D454, D456). The filtered signals are applied to the MAIN board via J481 (PA unit) and are then applied to the preamplifier circuit. D403, D408, D409, D406, D407, D410, D454, D453, D454 and D456 are varactor diodes that tune the ceinter frequency of an RF passband for wide bandwidth receiving and good image response rejection. On the VHF band, receiving signals are above 129 MHz, the switching diodes (D404, D405) are turned off by the control signal “2MBL” from PLL unit, then the varactor diodes (D408, D407) are disconnected. • Used RF high-pass filter (HPF board) • Used RF low-pass filter (FILTER board) 3 - 1 SECTION 3 CIRCUIT DESCRIPTION • RECEIVER CONSTRUCTION 1st LO: 69.0415 MHz– 530.0115 MHz BPF LPF HPF 1st mixer D271 2nd LO: 60.0 MHz 2nd mixer D511 to AM demod. circuit (D761) to FM demod. circuit (IC791) [ANT1] 0.03–60 MHz LPF [ANT2] 60–470 MHz Crystal filter FI511 69.0115 MHz Crystal filter NB gate FI561 to WFM detector circuit (IC631) to BFO circuit (IC1041) 9.0115MHz NB circuit FILTER BOARD PA UNIT HPF BOARD MAIN BOARD SSB, CW filter FI671 AM, FM-N filter FI681 Optional filter-1 Optional filter-2 amp. Pre-amp. IC151 Frequency (MHz) 0.03–2 MHz 2–4 MHz 4–8 MHz 8–15 MHz Frequency (MHz) 15–22 MHz 22–30 MHz 30–60 MHz Control signal L5 L6 L7 Control signal L1 L2 L3 L4 Entrance coil RL15 RL13 RL5 RL9 Entrance coil RL11 RL7 RL3 Frequency (MHz) 0.03–2 MHz 2–4 MHz 4–8 MHz 8–15 MHz Frequency (MHz) 15–22 MHz 22–30 MHz 30–40 MHz 40–60 MHz Control signal L5H L6H THH B7H Control signal THH L2H L3H L4H Entrance coil D111 D121 D131 D141 Entrance coil D151 D161 D111 D171 Downloaded from www.Manualslib.com manuals search engine

3-1-3 PREAMPLIFIER CIRCUIT (MAIN BOARD) The preamplifier circuit in the IC-706MKIIG has approx. 15dB gain over a wide-band frequency range. When the preamplifier is turned ON, the signals from the RF circuit are applied to the preamplifier (IC151) via D2182. Amplified or bypassed signals are applied to the 1st mixer circuit (D271). 3-1-4 1ST MIXER CIRCUIT (MAIN BOARD) The 1st mixer circuit mixes the receive signals with the 1st LO signal to convert the receive signal frequencies to a 69 or 70.7 MHz 1st IF signal. The signals from the preamplifier circuit, or signals which bypass the preamplifier, are passed through a low-pass filter and then applied to the 1st mixer (D271). The 1st LO signals (69.0415–539.0115 MHz) enter the MAIN board from the PLL unit via J281. The LO signal is amplified at IC281, filtered by a low- pass filter, and then, applied to the 1st mixer. 3-1-5 1ST IF CIRCUIT (MAIN BOARD) The 1st IF circuit filters and amplifies the 1st IF signals. The 1st IF signals are applied to a Crystal Filter (FI511) to suppress out-of-band signals. The 69 MHz 1st IF signals (except WFM) pass through the crystal filter (FI511), however, the 70.7 MHz 1st IF signal (WFM) passes through a bandpass filter (L501–L505, C501–C506). Then the filtered signals are applied to the IF amplifier (IC521). The AGC voltage is supplied to the transmit/receive switching circuit (D521, D522) and D521/D522 function as PIN attenuators for AGC operation. The amplified signals are then applied to the 2nd mixer circuit (D551) via the bandpass filter (L542–L546, C542–C545). 3-1-6 2ND MIXER CIRCUIT (MAIN BOARD) The 2nd mixer circuit mixes the 1st IF signals and 2nd LO signal (60.00 MHz) to convert the 1st IF to a 2nd IF. The 1st IF signals from the band pass filter (L542–L546, C542–C545) are converted to 9 MHz or 10.7 MHz 2nd IF signals at the 2nd mixer (D551). The 2nd IF signals are applied to the bandpass filter (FI561) to suppress undesired signals, such as the 2nd LO signal, and are then applied to the noise blanker gate (D561, D562). While in WFM mode, the IF signals pass through the low- pass filter (L601, C601–C603), IF amplifiers (Q601, Q611), ceramic filter (FI611). The signals are then applied to the WFM demodulator circuit (IC631). 3-1-7 NOISE BLANKER CIRCUIT (MAIN BOARD) The noise blanker circuit detects pulse type noise, and turns OFF the signal line when noise appears. A portion of the signals from FI561 are amplified at the noise amplifiers (Q621, Q632, amplifier section of IC631), then detected at the noise detector (D632) to convert the noise components to DC voltages. The converted voltages are then applied to the noise blanker switch (Q634, Q635). At the moment the detected voltage exceeds Q634’s threshold level, Q635 outputs a blanking signal to close the noise blanker gate (D561, D562) by applying reverse-biased voltage. The detected voltage from D632 is also applied to the noise blanker AGC circuit (Q631, Q633) and is then fed back to the noise amplifier (IC631) as a bias voltage. The noise AGC circuit prevents closure of the noise blanker gate for long periods by non-pulse-type noise. The time constant of the noise blanker AGC circuit is determined by R637. The 2nd IF signals from the noise blanker gate are then applied to the 2nd IF circuit. 3-1-8 2ND IF CIRCUIT The 2nd IF circuit amplifies and filters the 2nd IF signals. The 2nd IF signals from the noise blanker gate (D561, D562) are amplified at the IF amplifier (IC571) via the Tx/Rx switch (D572) and applied to a 2nd IF filter as shown below. The filtered or bypassed signals are applied to the buffer amplifier (Q721), IF amplifiers (Q731, Q741) and buffer amplifier (Q751) to obtain a detectable level at the demodulator circuit The amplified signals from the buffer amplifier (Q751) are shared between the SSB/CW/RTTY detector (IC841), AM detector (D761) and AGC detector (D771). Output signals from the buffer amplifier (Q721) are applied to the FM IF IC (IC791). 3 - 2 • 1st IF frequency • 2nd IF frequency • Used 2nd IF filter Mode Used filter Control signal SSB, CW, RTTY AM nar. AM, FM nar. FM SSB nar. CW nar., RTTY nar. SSB wide, CW wide, RTTY wide FL-272 (FI671) FL-94 (FI681) Bypassed Optional FL-223 Optional FL-100, FL101, FL-223, FL-232 Optional FL-103 2F23 2F80 2FTH OP1 or OP2 OP1 or OP2 OP1 or OP2 1st IF 69.0115 MHz 69.0100 MHz 69.0106 MHz 69.0105 MHz 70.7000 MHz Mode SSB/AM-N/FM AM/FM-N CW RTTY WFM 2nd IF 9.0115 MHz 9.0100 MHz 9.0106 MHz 9.0105 MHz 10.7000 MHz Mode SSB/AM-N/FM AM/FM-N CW RTTY WFM Downloaded from www.Manualslib.com manuals search engine

3 - 3 3-1-9 IF SHIFT CIRCUIT (MAIN BOARD) The IF shift circuit shifts the center frequency of IF signals to electronically shift the center frequency. The IF shift circuit shifts the 1st LO and BFO within ±1.2 kHz in SSB/CW/RTTY modes or ±250 Hz in CW-N/RTTY-N modes. As a result, the 2nd IF (also 1st IF) is shifted from the center frequency of the 2nd IF filter (FI671, FI681 or optional IF filters). This means 2nd IF signals do not pass through the center of the 2nd IF filter. Therefore, the higher or lower frequency components of the IF are cut out. Since the BFO frequency is also shifted the same value as the 1st IF, frequency is corrected at the detector. In the IC-706MKIIG, the 1st LO frequency is shifted to change the 2nd IF because a fixed 2nd LO frequency (60 MHz) is used. The 1st IF filter (FI671) and crystal filter (FI561) have 15 kHz pass-band widths, and do not affect IF shift operation. 3-1-10 AGC CIRCUIT (MAIN BOARD) The AGC (Automatic Gain Control) circuit reduces IF amplifier gain to keep the audio output at a constant level. The receiver gain is determined by the voltage on the AGC line (Q776 collector). The 2nd IF signal from the buffer amplifier (Q751) is detected at the AGC detector (D771) and applied to the AGC amplifier (IC811b). IC811b sets the receiver gain with the [RF/SQL] control via the “RFGV” signal line. When receiving strong signals, the detected voltage increas- es and the AGC voltage decreases via the DC amplifier (Q776). The AGC voltage is used for the bias voltage of the transmit/receive switching PIN diodes (D521, D522, D572, D573) to attenuate the received signals. When AGC slow is selected, C775 and R778 are connected in parallel to obtain appropriate AGC characteristics. 3-1-11 S-METER CIRCUIT (MAIN BOARD) The S-meter circuit indicates the relative received signal strength while receiving by utilizing the AGC voltage which changes depending on the received signal strength. The output voltage of the AGC amplifier (IC811b, pin 7) is applied to the main CPU (IC2001, pin 36) as an S-meter signal via the analog switch (IC2101, pins 5, 3) as the “SML” signal. The FM S-meter signal from the FM IF IC (IC791, pin 12) is also applied to the analog switch (IC2101, pin 5) via the meter amplifier (Q774). The S-meter signal from the main CPU (IC2001) is applied to the sub CPU and is then displayed on the S-meter read- out. 3-1-12 SQUELCH CIRCUIT (MAIN BOARD) The squelch circuit mutes audio output when the S-meter signal is lower than the [RF/SQL] control setting level. The S-meter signal is applied to the main CPU (IC2001, pin 36) in SSB/CW/RTTY modes and is compared with the threshold level set by the [RF/SQL] control. The [RF/SQL] setting is picked up at the sub CPU (DISPLAY board; IC1, pin 99). The main CPU compares the S-meter signal and [RF/SQL] setting, and controls the AF selector switch (IC861) to cut out AF signals via IC2122a. In FM mode, a portion of the AF signals from the FM IF IC (IC791, pin 9) are applied to the active filter section (pin 8) where noise components above 20 kHz are amplified. The signals are rectified at the noise detector section and then output from pin 14. The noise squelch signal from pin 14 is applied to the main CPU (IC2001, pin 31) via the analog switch (IC2101, pins 14, 13) as the “NSQL” signal. The CPU then controls the AF selector switch (IC861). 3-1-13 DEMODULATOR CIRCUITS (MAIN BOARD) (1) SSB/CW/RTTY modes The 2nd IF signals from the buffer amplifier (Q751) are mixed with the BFO signal from the PLL unit at the product detector (IC841, pin 6). The detected AF signals from IC841 (pin 1) are applied to the AF selector switch (IC861, pin 12). (2) AM mode The 2nd IF signals from the buffer amplifier (Q751) are detected at the AM detector (D761). The detected AF signal is applied to the AF selector switch (IC861, pin 15). (3) FM/FM NARROW modes The 2nd IF signals from the buffer amplifier (Q721) are applied to the FM IF IC (IC791, pin 16) where the IF signals are converted into 455 kHz IF signals. The signals pass through FI791 and are applied to the quadrature detector section. X791 is used for quadrature detector. The detected AF signals from pin 9 are then applied to the AF selector switch (IC861, pin 14) via the de-emphasis circuit (IC811a). (4) WFM mode The 2nd IF signals from the IF amplifier (Q611) are applied to the WFM demodulator circuit (IC631, pins 2, 3) where the IF signals are converted into AF signals. The detected AF signals from pin 8 are then applied to the AF selector switch (IC861, pin 11). • AGC CIRCUIT AGC line RFGV (RF gain control) AGC FAST Q771 8 V D771 C771 C772 2nd IF signal C775 R778 Q773 C774 R777 Q772 C773 R776 R775 D772 R772 R773 R774 Amp. AGC amp. Q776, Q777 IC811b “SML” AGC det. S-meter signal Downloaded from www.Manualslib.com manuals search engine

3 - 4 3-1-14 AF SELECTOR SWITCH (MAIN BOARD) The AF signals from one of the detector circuits are applied to the AF selector switch (IC861). IC861 consists of dual 4- channel analog switches which are selected with a mode signal and the squelch control signal. 3-1-15 AF AMPLIFIER CIRCUIT (PLL UNIT) The AF amplifier amplifies the demodulated signal to a suit- able driving level for the speaker. The AF signals from the AF selector switch (MAIN board; IC861) are applied to the PLL unit via the “AFI” signal line. The CW side tone/beep tone and optional synthesized voice are also applied to the PLL unit via the “AFBP” signal line. The AF signals from the MAIN board are applied to the VCA (Voltage Controlled Amplifier) circuit (IC201). The AF gain setting from the main CPU is converted to DC voltage at the D/A converter (MAIN board IC2201) and applied to the VCA control terminal (IC201, pin 8) via the “AFGC” signal line. The output AF signal from IC201 (pin 9) is power-amplified at IC231 to drive the speaker. 3-2 TRANSMITTER CIRCUITS 3-2-1 MICROPHONE AMPLIFIER CIRCUIT (MAIN BOARD) The microphone amplifier circuit amplifies microphone input signals and outputs the amplified signals to the balanced modulator or FM modulation circuit. Audio signals from the front or rear panel [MIC] connector enter the microphone amplifier IC (IC931, pin 22) and are then amplified at the microphone amplifier or speech com- pressor section. Compression level is adjusted with the [COMP GAIN] control (R945). The amplified or compressed signals are applied to the VCA section of IC931. The microphone gain setting from the D/A converter (IC2201, pin 2) is applied to the VCA control terminal (IC931, pin 10). The resulting signals from pin 9 are then applied to the buffer amplifier (Q961) via the analog switch (IC1141). External modulation input from the [ACC] socket (pin 11) is also applied to Q961. While in SSB mode, the amplified signals from the buffer amplifier (Q961) are passed through the AF selector switch (IC971) and are then applied to the balanced modulator (IC1041). While in AM/FM mode, the amplified signals from the buffer amplifier (Q961) are applied to the limiter amplifier (IC981a) and splatter filter (IC981b). The signals are then applied to the AF selector switch (IC971) in AM mode or to the varactor diode (D1012) in FM mode. 3-2-2 VOX CIRCUIT (MAIN BOARD) The VOX (Voice-Operated-Transmission) circuit sets transmitting conditions according to voice input. When the VOX function is activated, the microphone signals from IC931 (pin 19) are applied to the VOX comparator section in the main CPU (IC2001, pin 32) via the VOXL line. A portion of the power amplified AF signals from the AF power amplifier (PLL unit; IC231) are amplified at the buffer amplifier (IC931, pins 14, 15) and applied to the anti-VOX comparator section in the main CPU (IC2001, pin 33) via the AVXL line. Then the main CPU compares these and controls the transmitter circuit. 3-2-3 BALANCED MODULATOR (MAIN BOARD) The balanced modulator converts the AF signals from the microphone amplifier to a 9 MHz IF signal with a BFO (Beat Frequency Oscillator) signal. Microphone signals from the AF selector switch (IC971) are applied to the balanced modulator (IC1041, pin 1). The BFO signal from the PLL unit is applied to IC1041 (pin 10) as a carrier signal. IC1041 is a double balanced mixer IC and outputs a double side band (DSB) signal with –40 dB of carrier suppression. R1045 adjusts the balanced level of IC1041 for maximum carrier suppression. The resulting signal passes through a 9 MHz IF filter (FI671 in SSB/CW/RTTY modes) to suppress unwanted side-band signals. In AM mode, R1042 is connected to upset the balance of IC1041 via Q1041 for leaking the BFO signal as a carrier signal. The CW keying/RTTY TX signal is applied to IC1041 pin 1. • AF selector switch 11 13 INH 15 12 9, 10 14 X3 X2 X0 X X1 SSB/CW/ RTTY IC861 FM WFM AM 6 AFS1, AFS2 SQL AFI signal to PLL unit • Microphone amplifier 11 2, 3 10 19 22 9 14 15 MIC signal IC931 [COMP GAIN] (R945) MIGV from D/A convertor (IC35) VOXL to CPU AVOXL to CPU AFO signal Amp. COMP Buffer Buffer Buffer COMS from CPU AMOD to IC1141 VCA Buffer Downloaded from www.Manualslib.com manuals search engine

3 - 5 3-2-4 FM MODULATION CIRCUIT (MAIN BOARD) The microphone signals from Q961 are applied to the limiter amplifier (IC981a) and the splatter filter (IC981b). The 1750 Hz European tone signal from the main CPU (IC2001 pin 40) is also applied to IC981a pin 2 for European repeaters. The sub-audible tone signal (67.0–254.1 Hz) from the main CPU (IC2001 pin 37) is also applied to IC981b pin 5 for repeater use. The resulting signals are applied to the VCO circuit (Q1011, D1012) via R1002 to change the reactance of the varactor diode (D1012) for FM modulation. The modulated signal is amplified at the buffer amplifier (Q1013) and bypasses the 9 MHz IF filter. 3-2-5 TRANSMITTER IF CIRCUIT (MAIN BOARD) The 9 MHz IF signal from the modulation circuit passes through the 9 MHz IF filter (FI671 in SSB/CW/RTTY modes; FI681 in AM/FM-N modes; through in FM mode). The signal is amplified at IC571, and then passes through the total gain adjustment volume (R579), and the crystal filter (FI561). The signal is then applied to the 2nd mixer (D551). The signal is mixed with the 2nd LO signal (60 MHz) and converted to a 69 MHz IF signal at the 2nd mixer (D551). The 69 MHz IF signal passes through a bandpass filter, IF amplifier (IC521) and 69 MHz IF filter (FI511), and is then converted to the displayed frequency at the 1st mixer (D271) with the 1st LO signal. The mixers (D271, D551) and IF amplifiers (IC521, IC571) are used commonly for both receiving and transmitting. The ALC voltage is supplied to the transmit/receive switching circuit (D521/D522 and D572/D573). D521/D522 and D572/D573 function as PIN attenuators for ALC operation. 3-2-6 RF CIRCUIT (PA UNIT, MAIN AND HPF BOARD) The RF circuit amplifies the displayed frequency signal to obtain 100 W of RF output power for HF/50 MHz bands and 50 W for the 144 MHz band, 20 W for the 440 MHz band. The HF/50 MHz RF signals from the 1st mixer (D271) via the low-pass filter enter the HPF board and then pass through one of 8 high-pass filters (Refer to 3-1 for used RF high-pass filter). The 50 MHz RF signals pass through a low-pass filter additionally. The filtered signals return to the MAIN board, are amplified at the YGR amplifier (IC231), and are then applied to the PA unit. The 144 MHz RF signals from the 1st mixer (D271) via the low-pass filter (L251–253, C253–259) bypass the filters and pass through the bandpass filter (L182–L184, L195, L196, C181–C186, C195–C197) in the MAIN board. The signals are amplified at the RF amplifier (IC221) and YGR amplifer (IC231) and are then applied to the PA unit. The 440 MHz RF signals from the 1st mixer (D271) via the low-pass filter (L251–253, C253–259) are amplified at RF amplifier (IC222) and passed through the bandpass filter (FI371–FI373) in the MAIN board. The filtered signal is amplified at the YGR amplifer (IC231) and is applied to the PA unit. The signals from IC231 enter the PA unit and is amplified at the drive amplifiers (Q101, Q121) in sequence. The amplified signals are applied to the band switch (RL1). The HF/50 MHz RF signals from the band switch (RL1) are amplified at the drive (DRIVER board; Q161) and power (Q171, Q172) amplifiers to obtain a stable 100 W of RF output power. The power-amplified signals are then applied to the [ANT1] connector via one of the 7 low-pass filters in the FILTER board. For the 144/440 MHz RF signals from the band switch (RL1), 50 W for 144 MHz band or 20 W for 440 MHz band of RF output power is obtained at the drive (DRIVER board; Q211) and power amplifier (Q231). The power-amplified signals are applied to the [ANT2] connector via the antenna switching circuit and low-pass (144 MHz band) or high pass (440 MHz band) filters. 3-2-7 ALC CIRCUIT (MAIN BOARD) The ALC (Automatic Level Control) circuit reduces the gain of IF amplifiers in order for the transceiver to output a constant RF power set by the RF power setting even when the supplied voltage shifts, etc. The HF/50 MHz RF power signal level is detected at the power detector (FILTER board; D9), buffer-amplified at IC1b and applied to the MAIN board as the “HFOR” voltage. The 144 MHz and 440 MHz RF power signals are detected at the power detectors (PA unit; D262, D263) and (PA unit; D312, D313) respectively. The detected signals are applied to the MAIN board as the “VFOR” or “UFOR” voltages. • TRANSMITTER CONSTRUCTION 1st LO 60.0 MHz BFO FM tone D551 IC231 [ANT1] HF+50 MHz [ANT2] 144/440 MHz 144 MHz 440 MHz Q101 Q121 Q171 Q172 Q231 Q1011 D231 IC1041 IC931 Crystal filter FI1 FI671, FI681, or optional filter MIC except FM 9.0115 MHz Crystal filter BPF BPF LPF LPF HPF BPF HPF HPF PA UNIT HPF BOARD FILTER BOARD MAIN BOARD Amp. Amp. Amp. Amp. Q161 Amp. Amp. Q211 Amp. IDC FM, AM AM FM FM only 50 MHz 144 MHz SSB • • • BPF 440 MHz Downloaded from www.Manualslib.com manuals search engine

You're Reading a Preview

ICOM IC-706MKIIG Service Repair Manual

Description

Reviews

Q&A

Recently Viewed