Pioneer FX-K99DK WG Service Manual page 21

The TAPE +B2 (9.8V) is fed to PA3017 #30 via R68 and R72.
Then, PA3017 goes into the Dolby C mode. At this time, the
potential at #30 increases to 7V or a little higher but not to
9.8V. The reason for this is the same as that explained in
""When Dolby is off.'
d. Muting
This is an audio signal muting circuit. PD4022B #20 (MUTE)
keeps H {5V) level when the mechanism is shifting or in the
mode of FF, REW or MS. Then this signal goes through D17-2
and R82 and turns Q22 on. Then Vpp (5V) goes to
PA2014 #15 (MUTE) via D1 and R172. PA2014 mutes the au-
dio signal when the level at #15 is shifted to H (about 3V).
At the same time the VppD goes through R173, turns
Q41 (Q42) on and mutes PA2014's output. When loading and
ejecting, muting is also done in the same way as above with
the H (5V) signal coming out of #21 or #22. When switch-
ing the TUNER on and off, PD4050B #20(T MUTE) puts out | -
an H (5V) pulse. The pulse goes into O38 via R152, turns 038
on and mutes the audio signal.
e. Volume Control Circuit
The sound volume is controlled by the DC voltage fed from
buffer amplifier HA17358 in the Audio Unit to PAOOO5A
#12 (CONTROL IN) in Volume Unit via R3. The DC signal is
made by converting the 6-bit digital signal, which comes out
of PD40508, into an analog signal by a D-A converter made
of radder resistors. The control signal can theoretically be
varied in 64 steps (2°). But, PD4050B makes 32 steps of
different height (4, 2 or 1) to approximate the characteristics
curve ''C' of analog volume control. Fig. 30 shows the
characteristic of volume control type C.
When ATT (S7) is depressed, the output level of VOLUME data
is reduced to attenuate the sound volume by 20dB.
Vide
1o1t40
001 100+
Electronic sound volume data (digital)
pane 1
Saar 7 15 23 31 (Step)
Fig. 30 Volume control "Curve C"
w
1C2,IC3
PA3017
TAPE+B2 9.8V
R67 18
AUTO METAL
© Sit METAL
Ici
PD4022B
Fig. 31 Audio signal control circuit
R66
c
\7
Metal 2 5V FWD/REV METAL DOLBY NR
EJECT
1S Mute ON : 0.6V
ft
Mute ON | 3V HK)
R173
La
R145 R144 RIi43— R42 R125
R148 Ri32 -VR3
38 47 R93
R150 36] VRI
VRO
R146
Ic2 VDD vDD
PD4050B :
R160
20 = -RIS2 io
aS
VDD
Q22
)
R82