Icom IC-R3 Service Manual page 10

(2) TV MODE
The amplifed signals at the 2nd IF amplifier (Q857) are
applied to the bandpass filter (FI901). The filtered signals
are applied to the TV IF IC (IC901) as audio IF signal and
the video IF signal, separately.
IC901 is the video/audio detector IC of the PLL sprit type,
which contains the video IF amplifier, PLL video detector,
voice IF detector, IF and RF AGC, etc.
The audio IF signal from FI901 (pin 3) is applied to the TV IF
IC (IC901, pin 9) as the "SIF" signal, and is amplified and
phase detected in the IC. The phase detected signal is out-
put from pin 15, and is fed back to pin 13 via FI902. The fil-
tered signal is applied to the limitter amplifier section and
FM detector section in the TV IF IC.
The demodulated AF signals are output from pin 12 and are
applied to the AF circuit (LOGIC unit).
The video IF signal from FI901 (pin 4, 5) is applied to the TV
IF IC (IC901, pin 4, 5) as "VIF" signal, and is then amplified
at the video IF amplifier in the TV IF IC. The amplified signal
is compared with the VCO frequency (L902, C906), and is
then applied to the phase detector section in the TV IF IC.
The detected signal is output from pin 22 as the video sig-
nal, and then passed through the bandpass filter (FI905).
The filtered signal is amplified at Q854, and applied to the
buffer amplifier (Q855). The amplified signal is applied to the
TFT LCD circuit (LOGIC unit).
4-1-6 AF AMPLIFIER CIRCUIT (LOGIC UNIT)
The AF amplifier circuit amplifies the demodulated AF sig-
nals to drive a speaker.
While in FM and TV mode, AF signals ("FMAF" signal) from
the demodulator circuit (RF unit) are passed through the de-
emphasis circuit (R118, C66, C68) with frequency charac-
teristics of –6 dB/octave, and are then applied to the pre-
amplifier (Q31) via the bandpass filter (Q30).
While in AM mode, AF signals ("AMAF" signal) are pass
through the bandpass filter (Q30) and are then applied to the
pre-amplifier (Q31).
TV DEMODULATOR CIRCUIT
2nd IF signal from the
2nd mixer circuit (IC10, pin 6)
IF
amp.
D901
RF UNIT
"VIDEO" signal
LOGIC UNIT
to the TFT driver circuit (IC901)
AF signal from the
FM IF IC (IC2, pin 9)
IC901
TV IF IC
BPF
Q857
BPF
FI902
While in WFM mode, AF signals ("WFM" signal) are applied
to the pre-amplifier (Q31) directly.
The pre-amplified AF signals pass through the AF mute cir-
cuit (Q37) and are then applied to the electronic volume con-
trol circuit (IC14, pin 6). The level controlled AF signals are
output from pin 7 and applied to the AF power amplifier
(IC15, pin 1) via the buffer amplifier (Q36). The power ampli-
fied AF signals are applied to the internal speaker via the
[EXT SP] jack.
The electronic volume control circuit controls AF gain, there-
fore, the AF output level is according to the [VOL] setting
and also the squelch conditions. The AF mute and electron-
ic volume control circuits are controlled by CPU (IC11) via
each "AMUTE" and "VRC" signal lines.
When connecting [A/V OUT] jack (RF unit; J3) on TV mode,
AF signals from demodulator circuit (RF unit; IC901, pin 12)
are applied to the [A/V OUT] jack directly.
On AM, FM, WFM mode, AF signals from demodulator cir-
cuit (RF unit; IC2, pin 9) are applied to the RF amplifier (FM-
TV unit; Q71) via J5 (pin 1) on RF unit. The amplified signals
are applied to the [A/V OUT] jack via the J7 (pin 3).
4-1-7 TFT LCD CIRCUIT (LOGIC UNIT)
The amplified video signal from Q855 on MAIN unit is ampli-
fied at the buffer amplifier (Q903, Q904), and is then applied
to the OSD (On Screen Display) IC (IC902, pin 10). The
OSD IC produces LCD screen display data, and then out-
puts video signals to the TFT driver (IC901).
The TFT driver contains the procesing of RGB signal circuit,
color control circuit, etc. The TFT driver controls the TFT
LCD (DS4) using the video signals from the OSC IC.
4-1-8 SQUELCH CIRCUIT (LOGIC AND RF UNITS)
• NOISE SQUELCH
The noise squelch circuit cuts out AF signals when no RF
signals are received. By detecting noise components in the
AF signals, the squelch circuit switches the AF mute switch.
D914
audio signal
Buff.
Q854
video signal
Buff.
Amp.
BPF
FI905 Q854 Q855
OSD
Buff.
IC902 Q903,
Q904
4 - 4
"FMAF" signal
to the AF amplifier circuit
A/V OUT (RF unit; J3)