Pioneer KEX-70 Service Manual page 5

All the muting operations in the KEX-70 (KEX-73) are carried
out by the output section of the amplifier unit. A line trans-
former is used in this section to achieve a high common-mode
rejection ratio (CMRR).
Muting itself is performed by shorting the secondary (output
side) of the line transformer with transistors Q11 and Q12.
Muting is operational in the following circumstances:
(a) Fast forward and rewind operations
(b) A.T.S.C. (Automatic Tape Slack Canceller) operation
(c) Scanning and seek operations
(d) When the preset button has been depressed
(e) When the up/down button has been depressed
(f) When the reception band is switched over
(g) When the tuner goes OFF
Operations (a) and (b)
A positive voltage is supplied from PD2001 from mute input
pin Y, and 014 and Q13 are turned on. When Q14 and O13 are
ON, Q11 and 012 go ON and muting is effective. D11 func-
2.3 DESCRIPTION OF DECK CONTROL
IC PD2001
The PD2001 IC makes it possible to perform fast forwarding,
rewinding and direction change operation by feather-touch
control.
With every operation a muting output signal is fed out to the
PD2001 IC before the operation and a pre-muting circuit is in-
serted.
The KP-707G is included among the models which employ the
PD2001 IC and a description of its circuitry is given in Service
Manual (CRT-249) to which reference should be made.
Fig. 5 is used for this particular description. When an input is
fed into X1 for changing from the play to fast forward mode, a
muting output is first fed out and about 33ms later a voltage
virtually equivalent to the VDD is fed out to both OF and OR.
As a result, the fast forward and rewind solenoids are at-
tracted and the fast forward mode is established. The time
during which both solenoids are attracted is about 100ms. At
KEX-70/73
tions to prevent reverse current from mute input pin Z, and
the time constants of the muting operation are determined by
R90 and C57.
Operations (c)~(f}
A positive voltage is supplied from PD7004 from mute input
pin Z, and Q13 and Q14 are turned ON. When 014 and Q13
are ON, Q11 and Q12 turn ON and muting is effective.
Operation (g)
When the tuner is switched on (same for any band position), a
voltage (approx. 13V) is supplied from mute input pin X, and
C56 is charged through R92 and D12. At this point, Q15 re-
mains in the OFF mode and muting is not effective. Once the
tuner is switched OFF, the voltage from the mute input pin X
is rapidly reduced to OV. Q15 is turned ON when the charged
C56 discharges. Once 015 goes ON, Q14 and Q13 both go
ON, ultimately resulting in Q11 and Q12 being turned ON so
that muting is effective.
the same time, input X11 is set to the hold state by the latch cir-
cuit.
Once the time during which the fast forward and rewind sole-
noids are attracted has passed, the OF output is set to a high
impedance and so the fast forward solenoid is set to the hold
state with a voltage of about 2.5V determined by R76, R77,
R79 and D14. Furthermore, the OR output is grounded and
the rewind solenoid is released since no voltage is applied to
it.
When an input is fed into X3 next (changing from fast forward
to rewind), a voltage virtually equivalent to VDD is fed out to
OR and the mode is switched to rewinding. About 100ms later
the rewind solenoid is set to the hold state by a voltage deter-
mined by R76, R78, R80 and D14, and overheating of the
solenoid is prevented.
cn
FF
SOLENOID
Fig. 5