50Khz Step Indication; Elimination Of 1St Digit - Pioneer sx-d5000 Service Manual

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through TC5066BP (non-inverting buffer IC)
and applied to the anode segments (a thru g) of
the FL tube. Each digit shares the segments a
thru g connected in parallel, and each digit's
independent grid is sequentially scanned by the
pulses Ti1-Ti5,
displaying the selected station
frequency in a rapidly flickering display. The B,
C, and D data passed on the T4 pulse is not
actually frequency data (it is operation designa-
tion data to TC9123P-GR). Q45 conducts with
the appearance of T4, passing B, C, and D to
glound via D49-D51,
and thus avoiding un-
necessary data being sent to TCb022Bp. The
BL terminal of TC9L24AP outputs a display
blanking signal (Fig. 4- ) during the period the
time division pulses (T1-T4)
are in transition.
When this is applied to the BI terminal of
TC5O22BP, the output (a-g)
of TCb022Bp
goes low level regardless of the level of input
(A, B, C, D), thus preventing the blurring when
transition
is made from one display digit to
another.
With the appearance of Ti5, Q40 goes non-
conducting bringing the 5th digit data A, B, C,
and D all to a low level. This input state has the
same meaning as zero
frequency
data to
TC5022BP, thus a "0" is displayed as the bth
digit on the FL tube. (During FM reception.)
The FM/AM converter signal (low level during
AM reception) to the prescaler IC is applied to
the base of Q50, therefore Q50 is non-conduct-
ing during AM reception. Thus with the transit
of Ti5, the BI terminal (display blanking) of
'[C5022BP goes
to a high level, and all outputs
(a-a) are low level, extinguishing the bth digit
display during AM reception.
o 50kHz Step Indication (SX-D5000/S/G only)
The operation designation data for FM reception
for SX-D5000/S/G is FME. (See table g.)
During the FME mode, if data B is ,,1', (high
level) with
the transit of T4, + 50kHz shift
operation is performed. Thus, when data B is
at a high level with the transit of Ti5, the 5th
digit of the FL tube displays a "5".
Q40 goes off with the appearance of Tib.
If at this time data B is at a high level, A and C,
input to TC5022BP via D46 and D4? will go
high level. This input state (A and C high level,
B and D low level) mean a frequency data of
"5", thus the 5th
digit of the FL tube displays
a " 5 " .
o Elimination of lst Digit
Since there are 5 digits in the frequency display,
the 1st digit will be "0"
for any frequency
under AM 1000kHz and FM 100.00MH2. In
order to eliminate this zero (which in fact would
turn out to be a "L" since the 1st digit only
contains b and c segments), Ti4 is applied to
the RBI terminal of TC5022BP.
The 1st digit would be set to 0 when A is
switched to low level, but set to 1 when A is
switched to high level according to T4 timing.
And since Q45 is turned on at Ti4 timing, B, C
and D are switched to low level. The RBI
terminal input (Ti4) is inverted by NOT1 to
low level. So if A is switched to low level at T4
timing, the NAND2 inputs will both become
low level, and the output high level. The ORB
output
will thus be switched to high level,
resulting in all TC5022BP outputs being switch-
ed to low level. Hence, there will be no zero
display at the 1st digit.
F i g . 4 - 1 6 A n o d e s o f t h e F L T u b e D r i v e C i r c u i t
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