Hitachi KH 1230 H Service Manual

Page 2

MODEL KH-I23OH SERVICE MANUAL

CONTROLS AND JACKS

TELESCUPIC
ANTENNA

LIGHT

EUTTON
TUNlNr.

STE REO
IACKS a)?
EARPHONE _
JACK \
AC ADAPTOR
MACK

SQUELCH SWITCH

Fig. 1

Operating of Squelch Circuits-
Fig. Bshows the circuits pertaining to the squelch system.
Normal bias is applied to the base of TRl (transistor for
squelch system) and the collector current is flowed through
'the transistor when no signals are coming from the tuning
point. Since the collector current flows through the emitter
resistor R1 of TR2 (transistor for low-frequency amplifica-
tion), the base bias of TR2 changes to cut off its function
(transistor does not activate and, therefore, does not
amplify). Because of this principle, the noise is stopped at

TRZ and no noiseis emitted from the speaker.

FM DETECTOR

/\

BATTERY VOLTAGE 8:
TUNING METER

CONTROL
5?.

' (more swncu &
:g/ VOLUME CONTROL

VOLUME INDICATOR

BAND SELECTOR TOM: BUTTON

ff"

BATTERY COVER

Fig. 2

When signals come in an the tuning point, detected DC
signals add to the base of TRl to increase the bias in the
opposite direction, and consequently, to reduce the collector
current. Because of this principle, the bias for TRZ returns
to normal, the low-frequency amplification circuit activates,
and sound is emitted from the spEaker. In order for the noise
squelch to operate, the input signals level must be more
than 45dB for AM and 15dB forFM. When receiving weaker
signals than those specified above, squelch changeover must

be turned off.

FM

>4
M

VOLUME Connor.

:mrrzn
t

on 07F

SquLcN
sw l TON

anTAeE CHANGES wMEN
THERE ARE SIGNALS

WNEN TMERE ARE SIGNALS.
cuRRENY IS REOUCED To same
Bus of TR: BACK Y0 NORMAL
lAuPLiFIcAnoN REYURNS re
umuAL)

cuRNEMT Is REDUCED
WHEN WERE Ans SlGNALS.
(REDUCED cunniNT CHANGES BIAS UF 2)

Fig, 3

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n
3

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4. >4»: -M.mu. 35., <.