Icom IC-78 User manual

HF TRANCEIVER
iC-78

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
insulated 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 or 60 dB attenuator between
the transceiver and a deviation meter or spectrum
analyser when using such test equipment.
8. READ the instructions of test equipment thoroughly
before connecting equipment to the transceiver.
To upgrade quality, all 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 liq-
uids.
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-78 MAIN UNIT 1 piece
8810009130 Screw PH B0 M3 ×12 NI-ZU IC-78 CHASSIS 6 pieces
Addresses are provided on the inside back cover for your
convenience.
INTRODUCTION
This service manual describes the latest service information
for the IC-78 HF TRANSCEIVER at the time of publication.
Commercial
Commercial (w/alarm)
Marine
Marine (w/alarm)
OTH
OTH-1
OTH-2
OTH-3
#01
#02
#03
#04
SYMBOLVERSIONVERSION NO.

TABLE OF CONTENTS
SECTION 1 SPECIFICATIONS
SECTION 2 INSIDE VIEWS
SECTION 3 DISASSEMBLY INSTRUCTIONS
SECTION 4 CIRCUIT DESCRIPTION
4 – 1 RECEIVER CIRCUITS ................................................................................................................. 4 – 1
4 – 2 TRANSMITTER CIRCUITS .......................................................................................................... 4 – 4
4 – 3 PLL CIRCUIT ................................................................................................................................ 4 – 6
4 – 4 LOGIC CIRCUITS ........................................................................................................................ 4 – 6
4 – 5 POWER SUPPLY CIRCUITS ....................................................................................................... 4 – 8
SECTION 5 ADJUSTMENT PROCEDURES
5 – 1 PREPARATION BEFORE SERVICING......................................................................................... 5 – 1
5 – 2 PLL ADJUSTMENT ....................................................................................................................... 5 – 2
5 – 3 TRANSMITTER ADJUSTMENTS.................................................................................................. 5 – 4
5 – 4 RECEIVER ADJUSTMENTS......................................................................................................... 5 – 8
5 – 5 SET MODE ADJUSTMENT........................................................................................................... 5 – 10
SECTION 6 PARTS LIST
SECTION 7 MECHANICAL PARTS AND DISASSEMBLY
SECTION 8 SEMI-CONDUCTOR INFORMATIONS
SECTION 9 BOARD LAYOUTS
9 – 1 MAIN UNIT ................................................................................................................................... 9 – 1
9 – 2 PA UNIT......................................................................................................................................... 9 – 3
9 – 3 PLL UNIT ...................................................................................................................................... 9 – 3
9 – 4 LOGIC UNIT ................................................................................................................................. 9 – 5
9 – 5 PHONE BOARD............................................................................................................................ 9 – 5
9 – 6 MIC BOARD .................................................................................................................................. 9 – 5
9 – 7 VR BOARD.................................................................................................................................... 9 – 5
9 – 8 SENSOR BOARD.......................................................................................................................... 9 – 6
9 – 9 FILTER UNIT ................................................................................................................................. 9 – 7
SECTION 10 BLOCK DIAGRAM
SECTION 11 WIRING DIAGRAM
SECTION 12 VOLTAGE DIAGRAMS

SECTION 1 SPECIFICATIONS
1 - 1
■GENERAL
• Frequency coverage :
Receive 0.030–29.999999 MHz*1
Transmit 1.600–29.999999 MHz*2
*1Guaranteed range: 0.5–29.999999 MHz
*2Guaranteed range: 1.600–1.999999 MHz
3.500–3.999999 MHz
5.000–7.999999 MHz
10.000–29.999999 MHz
• Mode : USB, LSB, CW, AM, RTTY (FSK)
• Channel : 100 channel
• Frequency stability : Less than ±200 Hz from 1 min. to
60 min. after power ON. After that
rate of stability less than ±30 Hz/hr
at +25˚C (+77˚F). Temperature
fluctuations 0˚C to 50˚C (+32˚F to
+122˚F) less than ± 350 Hz.
•
Power supply requirement : 13.8 V DC ±15 %
(negative ground)
• Current consumption :
Transmit max. power 20.0 A
Receive stand-by 1.3 A
max. audio 2.0 A
• Usable temp. range : –10˚C to +60˚C (14˚F to 140˚F)
• Antenna connector : SO-239 (50 Ω)
• Dimensions : 240 (W) ✕95(H) ✕239(D) mm
(projection not included) 97⁄16(W) ✕33⁄4(H) ✕913⁄32(D) in
•Weight : 3.8 kg (8 lb 6 oz)
•ACC connector : 13-pin
•REMOTE connector : 2-conductor 3.5(d) mm (1⁄8")
■TRANSMITTER
•Modulation system :
SSB Balanced modulation
AM Low level modulation
•Output power :
SSB/CW/RTTY/FM 2–100 W
AM 2–40 W
•Spurious emission : Less than –46 dB below peak out-
put power
* spurious frequency ; below 30 MHz: –50 dB,
above 30 MHz: –60 dB
•Carrier suppression : More than 40 dB
•Unwanted sideband suppression:
More than 50 dB
•Mic. connector : 8-pin connector (600 Ω)
•KEY connector : 3-conductor 6.5(d) mm (1⁄4")
•SEND connector : Phono (RCA)
•ALC connector : Phono (RCA)
■RECEIVER
•Receive system : Double-conversion
superheterodyne
•Sensitivity (10 dB S/N) :
SSB, CW, RTTY 0.16 µV*1(1.8–29.999999 MHz)
AM 13 µV (0.5–1.599999 MHz)
2.0 µV*1(1.6–29.999999 MHz)
*1Pre-amp 1 ON
•Squelch sensitivity : Less than 5.6 µV (SSB)
•Selectivity :
SSB, CW, RTTY More than 2.1 kHz/–6 dB
Less than 4.5 kHz/–60 dB
AM More than 6.0 kHz/–6 dB
Less than 20.0 kHz/–40 dB
•Spurious and image rejection ratio:
More than 70 dB
(1.6–29.999999 MHz)
•Audio output power : More than 2.0 W
(at 13.8 V DC) at 10 % distortion with an 8 Ωload
•RIT variable range : ±1200 Hz
•PHONES connector : 3-conductor 6.5(d) mm (1⁄4")
•EXT SP connector : 2-conductor 3.5(d) mm (1⁄8") 8 Ω
All stated specifications are subject to change without notice or obligation.

9 - 4
VARISTOR BOARD
The combination of this page and the previous page
shows the unit layout in the same configuration as the
actual P.C. Board.
•BOTTOM VIEW (PLL UNIT) •BOTTOM VIEW (PA UNIT)

S-13707MZ-C1
© 2000 Icom Inc.
1-1-32, Kamiminami, Hirano-ku, Osaka 547-0003, Japan
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