Sharp Linytron C-1408T Serviceanleitung Seite 7

When the main switch is turned on later, the AFT
control output signal becomes "low" level (not allow-
ing the AFT circuit to operate) and the tuning voltage
is reset to such level as it had been before pushing the
FT (+) or FT (—) key was stopped.
Table 3 shows the speeds at which the tuning voltage
for each band can be finely adjusted.
Table 3. Required Time for Tuning Voltage Adjustment
Time required for band sweeping
About 640 sec (about 38.8 msec/step)
About 1280 sec (about 77.6 msec/step)
fa | 4 | U (UHF) About 1280 sec (about 77.6 msec/step)
(11) MEMORY key function
Operation of the memory key is effective only when
the unit is placed in the channel preseiting mode.
When the memory key is pushed during such mode, the
information data (tuning voltage, channel No., AFT
on/off) concerned with the channel being in selection
are written into the EAROM. With the memory key
pushed, the channel No. indicator stops flashing for
about 1 second and then it starts flashing again.
As to the channels changeable with the remote control,
they can't be stored in the memory.
(12) Tuning voltage output (D/A)
As shown in Fig. 4, there are caused pulse-modulated
signals at the pin D/A of the IC (IC1001) and their
generation depends on the 14-bit digital information
data.
The period To (about 122 Hz) is divided into 64
sub-periods each of which is called Ts (about 7.6
kHz), and the sub-period Ts is 256 times larger than
the minimum pulse width To = 550 msec (2 MHz).
The length of each sub-period Ts is referred to as Tm
(m = 1 ~ 64) and it is decided by the following:
The 14-bit data comprises 6-bit data (LSB) and 8-bit
~data (MSB).
Now suppose that the 8-bit data is of LSBo91 1000058
and the 6 bit data is of LSBoQ000 . In this case, the
length Tm of each sub-period Ts will be 12 to for all
of T, to Te4.
Then if the tuning voltage is increased by one step,
the 6-bit data will be of 100000, and with this data
given, the length of the sub-period T3. will be 13 to
while that of each of the other sub-periods will be 12
to. And if the tuning voltage is increased by another
one step, the 6-bit data will be of 010000, and in this
case, the two sub-periods T,, and Ty, will be of 13
to in length while the other sub-periods will all be of
12 to in length.
If the tuning voltage is increased in this way until the
6-bit data becomes 111111, the sub-period Tg, will be
of 12 to in length and the other sub-periods T, to T¢3
| C-1408T
Loot Ey To T3,! Ta! Tat LSB ooo S®
LLL LS 0000
6
Figure 3. Waveform of D/A Output
m8, 24, 40,56
m = 2, 6, 10, - - -—-— 58, 62
P0001 [m= 13,5,
663
|
if
To tuner
-D/A
1 a ae
Figure 4. Filter Circuit (as an example)
(13) Auto clear circuit
The circuit as shown in Fig. 5 is attached to the auto
clear pin AC of the IC (IC1001) so as to cause the unit
to be deprived of all the functions for a while when the
power switch is turned on.
+B power supply
M50124-001SP