Kenwood TH-77A Service Manual page 16

IA-/fA/E
1. Control Unit (X53-333X-XX)
Reference No. Function
Q1
5RUC/S5RUOM switch
Q2
5RV/5CV switch
5RVC/5RU switch
5RVOM/5CU switch
5C/5R AVR
Device Functions
Description
5RUC: Power switch in the stage after the UHF receiver mixer
5RV: VHF receiver RF amplifier/mixer power switch 5CV: VHF PLL power switch
5RVC: Power switch in the stage after the VHF receiver mixer 5RU: UHF receiver RF
amplifier power switch
5RVOM: Subband UHF receiver power switch 5CU: UHF PLL power switch
5C/5R AVR error amplifier
Save operation switch
5T AVR
5T AVR error amplifier
5TV switch
Microphone input shorting switch
The amplifier is turned on when Q7 is turned on or off.
1/2: Off during save operation. 2/3: On during transmission.
The amplifier is turned on when Q7 is turned on or off.
On during VHF transmission.
On while DTMF signa! is modulated.
Modulation output band switch
CTCSS input selection control
Main audio high-pass filter
Sub-audio high-pass filter
AF amplifier regulator
AF amplifier regulator
AF regulator switch On when AF signal is output.
Microcomputer reset switch
5M/CTCSS power switch
Lamp LED constant-current source
foa2 | aatswitch | On when lamplights
[023 | DTM decoder input selection control |
[01 | Power reverse-connection protection diode |
[02 | AFIC BY pinvottage drop prevention |
[03 | AFIC BY pin voltage drop prevention |
[D4 | AFICAVR time-constantcontrol
[05 | AFICBY pinreverse-tiow prevention |
Df ee ee
Dae age re ee
Pi Oe ee ee ee
Low for 1 ms when external power is supplied.
1/2: Power circuit reference voltage on/off 2/2: On during CTCSS operation.
| Ds_____| Microcomputer backup battery selection
[D8 | BacklightteD
D9 Backlight LED
Backlight LED
Backlight LED
Backlight LED
Backlight LED
—
Electrostatic surge absorption
Microphone amplifier
DTMF/CTCSS decode selection
Selection of AF signal to main band and
sub-band
Selection of AF signal to internal/external
AF amplifier
External audio power amplifier Connected to external speaker socket.
Internal audio power amplifier Connected to interna! speaker.
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