Sharp GF-575H Service Manual page 12

@ Normal speed/high speed playback selector circuit
Being provided at the deck 1, the NF circuit works to select
the normal speed mode or the high speed mode: the
frequency at the high speed is two times higher than that at
the normal speed. Here is also given proper equalization for
the signals of both speed modes. 1C102 changes its constant
according to whether a normal tape or a metal tape has
been loaded in the unit.
@ Normal speed/high speed record selector circuit
Being provided at the deck 2, the circuit made up of
transistors Q277, Q278, Q279 and Q280 works to select
the normal speed mode or the high speed mode: the
frequency at the high speed is two times higher than that at
the normal speed. Transistors 0275 and Q276 are used to
detect whether a normal tape or a metal tape has been
loaded in the unit.
e Normal speed/high speed selector circuit
Change of the motor's rotational speed results in a
changeover between the tape normal speed and high speed
modes. The electronic switch is used to act on the deck 1
and deck 2 at a time as their speeds are changed.
Fig. 18-2 shows how the circuit works to get the unit in the
high speed mode, whose expression is made with use of the
mechanical switch instead of the electronic switch.
m™ APPS (Automatic Program Pause System)
The existing APLD, as you know, is to automatically detect an
end of the program when the unit is in fast forward or rewind
mode and then to return it to play mode. The APPS employed
for the GF-575H/E is something new which is based on the
same ideas as with such APLD, and it is activated not only
when the unit is in play mode (at the deck 1 only) but also
when it is in dubbing mode (from the deck 1 to the deck 2).
In the dubbing mode (either at normal speed or at high speed),
as soon as an end of the program is detected by the APLD in
the deck 1, the APPS works to stop the motor circuits of both
decks 1 and 2 simultaneously — that is, motions of the deck 1
and deck 2 are stopped just at a time.
Therefore, the deck 1 has two automatic controls — APLD and
APPS, that is, it is controlled by the APLD when it is in play
mode (with the deck 2 in stop mode) and by the APPS when it
is in dubbing mode.
The two cotnrols APLD and APPS are differentiated by the
following:
@ Difference in gain and frequency characteristic between
APLD and APPS.
@ Difference in program detect time between APLD and
APPS
These differences are due to that the tape speed is different
according to whether the unit is in play mode or dubbing
mode, and according to these, the electronic switch selects the
APLD or APPS to get it in action.
Deck 4 Deck 2
O_O} owe (eKe)
=n 'a,
Playback Record
circuit circuit
Wave length Wave length Wave length of
on a tape on the circuit the recorded signal
Normal
speed a
mode
Hi
od
—~
l \
To be shortened =
mode Twice as fast tole Twice as fast
as the normal
tape speed
as the normal
tape speed
The deck 1 and
deck 2 have the same
signal wave length.
Figure 18-1
Deck 2
Deck 2 record/play
Play switch switch
High R P Radio
Normal
Noy | | =
Vota so
906
speed
O
Deck 1
Dubbin A
Motor selector
Normal ce) switch
play switch
Oo
transistor speed
switch
Deck 1 playback equalization selector
Deck 2 record equalization selector
Figure 18-2
Time
constant
change
Schmidt
circuit
FF/REW
PLAY
Program
interval
detected
signal
FF/REW
PLAY
Shift
resistor
Figure 18-3
—18—
Function selector