Yamaha tx7 Service Manual page 14
Fm tone generator
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Also See for tx7:
- Owner's manual (49 pages) ,
- Performance notes (37 pages) ,
- Performance notes (37 pages)
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2.
The
voltage
at
point
A
increases,
and works
to increase
the
Trj
collector
current.
Therefore,
Tri
instantly
saturates,
and
there
is
no
more
time
difference
in
the
current flowing
in
Lj
,
so
there
is
no
more
induced
voltage
in
L
2
.
At
this
time,
reverse
electromagnetic
force
(accumulated energy)
is
generated,
and
this
energy
indvces voltage
in
L
3
.
When
this
happens, the
base of
Tr!
will
have
reverse
bias
because of
the reversed
e.m.f.
in
L
2
,
and
Trj
will
go
OFF.
3.
Next,
when
the
accumulated
energy
of Lj
is
released,
base current flows again to Trj
through
Rj.and
Tr
t
will
begin operating
again.
In
this
way,
the desired voltage
is
attained
as
the
ac-
cumulated
energy
in
Lj
is
released to
L
3
by
the switching
action of Trj
.
The
actual circuitry
of the
TX7
is
as follows.
The
following
is
a
block
diagram
of
the
TX7
power
supply.
o-j
Noi* L
1
filter
r
Control
j
cHlRectt^—
O
+
5V
-figr
|
—
OCN0
Error
Circuit
Diagram
1
1
oAS—
lS(Ci-i;
to
AS
-Aft
fn
3)
ft)
AS-
D&
CC1-5J
to
AS- DO
(C?
-4)
fCi-tJ
trAS-tS
rci-7>
to
AS-+5
rci-4
>
1
.
In
diagram
1
2 the
base driving
circuit
is
D
2
,
Ci and
R
2
.
This controls the base current of Tr*
through
R
2
.
2.
Tr
2
controls the base
current
of
Tr
1(
thus
controlling
the voltage that
appears
in
the secondary.
i.
tu*
m\
wnm
w
nmm
tto
ttuetua.
tion of the
+5V, and
feeds
back the
fluctuation to the
control
circuit
through
a
photocoupler PCj
(which
electrically isolates
the
primary and
secondary).
4.
On
the
basis
of the
information
fed back
to
it,
the
control
circuit increases
the base current
of
Tr
2
,
and by
thus changing the
oscillating
frequency
of
Tr,, controls
Diagram 12
the
output
voltage.
The
output
voltage
(+5V)
may
be
adjusted using the
VRi
connected
to the base of
Tr
3
in
the
error
detection
circuit.
The power
switch
SWj
turns the voltage to the emitter of
Trj
on and
off.
Thus,
as
the converter
circuit
switches or
does not
switch, voltage
is
generated
or
stopped
in
the
secondary. Therefore, even
when
the
power
switch
SWj
is
off,
voltage
is
present
at
the
primany,
so
when
servicing,
please
be
careful.
-
25
-
TX7
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