Icom Ic-2800 Dual Band Fm Tranciever Service Manual

A-5570MI-S
© 1999 by Icom Inc.
6-9-16, Kamihigashi, Hirano-ku, Osaka 547-0002, JapanCount on us!
DUAL BAND FM TRANSCEIVERiC-2800h
iC-2800h 

INTRODUCTION
This service manual describes the latest service information for 
the IC-2800H FM TRANSCEIVER at the time of publication.To upgrade quality, all electrical or mechanical parts and   inter-
nal 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.  Such a connection 
could cause a fire hazard and/or electric shock.
DO NOT 
expose the transceiver to rain, snow or any liq-
uids.
DO...

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 – 3
4 - 3  PLL CIRCUIT...

MGENERAL
• Frequency range : 
*1Guaranteed 144.000 – 148.000 MHz only
*2Guaranteed 430.000 – 440.000 MHz only; *3Guaranteed 440.000 – 450.000 MHz only
• Mode : FM, AM (118.0 – 135.995; Rx only)
• Nomber of memory channel : 232 (incl. 6 pairs of scan edges, 10 log, 10 repeater and 2 call channels)
• Usable temperature range : –10˚C to +60˚C; +14˚F to +140˚F
• Frequency resolution : 5, 10, 12.5, 15, 20, 25, 30 and 50 kHz
• Frequency stability : ±10 ppm (–10˚C to +60˚C; +14˚F to +140˚F)
• Power supply...

2 - 1
SECTION 2 INSIDE VIEWS
• CONTROL UNIT
• MAIN UNIT
* : Located underside of this point
* : Located underside of this point
Q15
Q19
Q20Q14
V-VCO circuit 
Main CPU
(IC19: HD6433876N) 
EEPROM*
(IC17: X25320SI) PLL IC*
IC2 M64076AGP
U-VCO circuit 
UHF FM IF IC*
(IC8: TA31136FN)
MIC amplifier*
(Q88: 2SC4081)
PLL reference oscillator
(X1: CR-549 15.2 MHz) UHF antenna 
switch 
(D27*, D37, 
 D39, D72)
UHF 1st mixer 
(Q42, Q43, D32)
VHF antenna 
switching
(D9*, D16, D18)
VHF power module*
(IC1: M67746) VHF...

3 - 1
SECTION 3 DISASSEMBLY INSTRUCTIONS
• Removing the MAIN unit
qUnscrew 1 screw, A, and remove the cover.
wUnplug J4 to separate the fan motor from the MAIN unit.  
eRemove 2 main shield, 
B, and TR-A clip, Cin the direc-
tion of the arrow.  
• Removing the CONTROL unit
qUnscrew 4 screws, A, and remove the cover.
wUnplug J5 to separate the speaker and front panel.  
eRemove rear panel in the deirection of the arrow.  
rRemove 6 knobs, 
B.  
tUnscrew 5 screws, 
C, and remove the CONTROL unit in
the...

4 - 1
SECTION 4 CIRCUIT DESCRIPTION
4-1 RECEIVER CIRCUITS
4-1-1 DUPLEXER CIRCUIT
The transceiver has a duplexer (low-pass and high-pass fil-
ters) on the first stage from the antenna connector to sepa-
rate the signals into VHF and UHF signals. The low-pass fil-
ter (L15, L16, L78, C70–C72) is for VHF signals and the high-
pass filter (L44, L45, L82, C189, C190, C493) is for UHF sig-
nals. The separated signals are applied to each RF circuit.
4-1-2 VHF ANTENNA SWITCHING CIRCUIT
The antenna switching...

4 - 2
The 1st IF signal from the 2nd IF amplifier is applied to the
2nd mixer section of IC28 (pin 16), and is mixed with a 15.2
MHz 2nd LO signal generated by the reference oscillator cir-
cuit (X1, IC2) to produce a 450 kHz VHF 2nd IF signal.
The 2nd IF signal from the 2nd mixer passes through the 2nd
IF filter (FI4) (during wide channel spacing selection, or pass-
es through FI5 during narrow channel spacing selection;
[EUR], [ITA] versions only), where unwanted signals are
suppressed. It is then...

4 - 3
4-1-10 UHF RF CIRCUIT
The UHF RF signals are passed through part of a duplexer
(high-pass filter; L44, L45, L82, C189, C190, C493). The sig-
nals are then passed through the low-pass filter (L42, L43,
C187, C463), antenna switching circuit (D37, D39, D72), and
then amplified at the RF amplifier (Q44). A bandpass filter
(FI3) is used at the next stage of the RF amplifier. The RF
switch (D35, D33) turns on the UHF RF circuit when UHF sig-
nals are received.
4-1-11 UHF 1ST MIXER AND 1ST IF CIRCUITS...

4 - 4
4-2-5 VHF APC CIRCUIT
The APC circuit protects the power amplifier from a mis-
matched output load and stabilizes transmit output power.
The APC detector circuit (L12, D7, D8) detects forward sig-
nals and refrection signals at D7 and D8 respectively. The
combined voltage is at a minimum level when the antenna
impedance is matched at 50 ½and is increased when it is
mismatched. 
The detected voltage is applied to the APC amplifier (IC5, pin
3) and compared with a reference voltage which is supplied...