Technics SU-A80 - Circuit Operation and Servicing; Input Selector Circuit Logic Explanation; Equalizer Transistor Replacement Guide

Mi BASIC OPERATION OF INPUT SELECTOR CONTROL
CIRCUIT
The input selector contro! circuit is a flip-flop circuit using NOR gate.
NOR gate goes “‘L’’ when even one of the input terminals is at ‘‘H’’. For example, with tact
switch S1 depressed as shown below, the level of signal applied to input terminals of
The output of
and
I3 is “‘H”, and the output goes ‘’L’’. The outputs of 12 and I3 are applied to input terminals
of I1, causing only the level of 11 to go “‘H”. With S2 depressed, ‘‘H’’ is applied to input
terminals of 11 and 13, causing the output of I1 to change from “‘H” to ‘’L’’. The output is
then applied to 12 and I3, changing the output of |2 to ‘‘H” and that of 13 to “L’’. The
circuit of this unit is of 8-stage configuration as shown in the block diagram, and operates
as explained above.
Output
Output
Output
$2 depressed.
Parenthesized levels with
Output
terminal
¥'
Table of logic
A Input
B terminal
Mi
SERVICING
PARTS
FOR
EQUALIZER
DIFFERENTIAL
TRANSISTORS
(Q101~Q108)
The equalizer differential transistors (0101 ~ Q108) used in this unit are 2SK369. However,
when replacing the parts, be sure to use servicing repair parts 2SK146.
e Pairs replaced
When one of the parts in pair shown below is replaced, remove the other one as well and
insert 2SK146 instead.
Combination
e How to fit
@ 2SK146 includes 2 transistors. So, bend the legs as
shown and put 2 or 3mm tube on each gate leg to
1 2 3
Q101 Q102 Q105
t $ t
Q103 Q104 Q107
4
Q106
+
Q108
prevent shorting between the leads.
@ 2SK146 must be correctly inserted according to D,
G and S indicated on the surface.
Drain mark
Drain mark
Mi BLOCK DIAGRAM
PLAYBACK
REC OUT
*] 1C301~304
meee MNG663 1A
a; 216) mn Input selector (Voice signal)
PHONO Differen-—<« daw Pp 9
slit ses ssa) > oe =
Q101,103,
iets
Pa
tape-monitor
ind.
105,107 IclOl (172)
SVINJM4560DX
mc O MM MC O MM Equalizer és oft
Peles s101 Phono selector er. | ms
| a
ft
TUNER @— = \ ot |
on” ° S302 (TAPE 3) oNeiace,
co &
Tv/aux2 O—
VIDEO/AUX | eee
(FRONT)
S,
FRONT
VIDEO/AUX! (O
(REAR) CS
TAPE 3/
DA TAPE
TAPE 2/VTR
TAPE 1/EXT
TAPE 3/
DA TAPE
TAPE 2/VTR
TAPE 1/EXT
VIDEO O
(FRONT) S
TV IN
VIDEO
C305
MN6631A
Rec output selector
$301 a
\ideo input/auxiliary
jinput 1 terminal
selector
|
|
!
!
|
|
IC401
SVI ywPD4066BC
INPUT SELECTOR
1C402
SV1uPD4066BC
INPUT SELE
7'$753 (SOURCE) dies
{ ease Recording output
a on
OF | selector
(SOURCE) eth
off
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Rec output selector switch
°
|
i
on |
es
IC 403
? S3O3(TAPE 2)
S304(TAPE!)
Oo
off
$305
control
©) output
<6) INPUT
Computer
Mode
selector
$504
STEREO
Q212"0N"
] Computer control
Q50:
Bia
Subsonic filter
Input selector switch muting
‘lei
Output ‘’L”’
‘a ‘ with $251 pushed.
Output “L”
> with S252 pushed.
Output ‘’L”’
with $253 pushed.
Output “L”’
a with $254 pushed.
Output “’L"”
ft
| (TAPE 3) °
Q2il
on
off
(TAPE 2)
Q210
tv out ©
Buffer
with $255 pushed.
ee 3)
Se
O—-2
(VIDEO)
ae
a a
@205
Q206
Output “L”’ a
with S256 pushed.
s502
off oa 9505
} -
Differen ;
Q507,
Current
stabilizer
€8)
It turns “ON” whi
1C201,202
204,205
SVIluPD4002BC
Input selector control
1c203 I
1C203
(TAPE 1)
SI with $258 pushed.
g Q209
ja
J 2), ONG S303(TAPE 2)
0207
Output “‘L”’ |
with $257 pushed.
oft
a $304 (TAPE 1)
OS Q208
“Output “L" j <}