Sansui 7900Z - Page 19

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1-2. Tuner Section
( ] FM Frontend
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9900Z/89002ZDB/790
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307,90 FM Mute
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[Pee
<7900Z Only> {Piise
<29002 8900208 Only>
103 {FT
Generator
Circuit
2. OPERATIONS
A static-mode digital tuning system has been used for the tuner sec-
tions of Model 9900Z, 8900ZDB, and 7900Z. The system comprises
a Pre-scaler 1C/TD6104P, PLL synthesizer control IC/TC9140P and
a digital display driver 1C/TD6301P.
2-1. Main Function
A. Function of Tuning Selection
1) In 9900Z and 8900ZDB, a rotary encoder is adopted to realize a
novel manual tuning system, in-which the conventional analog
tuning system and digital tuning system are used together.
2) In 7900Z, one-step/one-push, manual tuning, fast forward
manual tuning, and automatic search tuning can be made by
depressing the AUTO/MANUAL selection switch and the UP/
DOWN key which are joined with each other.
3) The memory can write-in or read-out six FM broadcasting sta-
tions and six AM broadcasting station, respectively, by pushing
the MEMORY key (f$101) and the PRESET keys (fS102-fS107).
B. Display of Received Frequency
The received frequency can be displayed in two methods, simultane-
ously: analog dial display by LEDs and digital display by IC/
TD6301P.
C. Others
Upon the operations of the PRESET keys, FM/AM band selection,
and scanning, an approx. 2.5 kHz pulse signal! (as shown in Fig. 2-1)
is outputted for a fixed period from the terminal “Pee’’ of TC9140P,
so as to produce an operation-confirming pitch sound from the
buzzer (fSP1).
L-CH OUT
Signal, Tune
Drive Circuit
sits: 2~*
SIGNAL oomoa AM 9 j7]/7 77 KHE
tune wea FM / LILI mi
Fig. 2-1
FM/AM band Selection,Memory
read-out,Manual UP/DOWN
Manual fast forward, Automatic
scanning
2-2. Operation of Manual Tuning in 9900Z and
8900ZDB
In 9900Z and 8900ZDB, the manual tuning is performed by the use
of a rotary encoder including two photo-couplers, without depress-
ing the UP/ DOWN key.
The photo-couplers and a reflector mounted on the tuning knob de-
tect whether the tuning knob is being rotated clockwise to increase
(UP) the frequency or counterclockwise to decrease (DOWN) the
frequency to be received.
The two photo-couplers fPH51 and fPH52 detect the respective
positions with a phase difference of 90 degrees. Fig. 2-2 (a) shows a
mutual relationship between two output pulses of fPH51 and fPH52,
when the tuning knob is being clockwise; (b) shows a mutual rela-
tionship between two output pulses of fPH51 and fPH52, when the
tuning knob is being rotated counterclockwise. The two output
pulses are converted into an UP or DOWN pulse signal, respectively,
through a pulse generator circuit as shown in Fig. 2-3, and next fed
to the terminal UP or DOWN of TC9140P in order to increase (UP)
or decrease (DOWN) the frequency to be received. :