Mitsubishi LT-20 User manual

ate MITSUBISHI
AUDIO SYSTEMS
SERVICE MANUAL
LINEAR
TRACKING
TURNTABLE
MODEL
LT-20
CONTENTS
IDENTIFICATION AND OPERATION 1.0.2.0... 0000 cece eet ee ees 2
SCHEMATIC REPRESENTATION OF LT-20 AUTOMATIC FUNCTIONS ........0. 0.20000. cece eee 2
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INTERNAL DIAGRAMS AND PINOUT OF INTEGRATED CIRCUITS ................- Bok uaa ate 8
INFORMATION ON LOGIC IC (MSM-5831RS) 20... eee ee eee 10
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MITSUBISHI ELECTRIC SALES AMERICA, INC.
3030 East Victoria Street Compton, California 90221

| IDENTIFICATION AND OPERATION:
Light emitter Prism Main weight
i
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'
\
(
!
1
|
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i
1
i
QUARTZ
(Quartz
lock
indicator)
SPEED
(Speed
reset
button)
REPEAT
(Repeat
button)
A Il
4
Ed
[|
|
i
[|
(
—— =I
Power on: turn the locking arm of the
arm rest in a counterclockwise direction.
Tonearm becomes free.
START < (Start button)
SCHEMATIC
REPRESENTATION
OF
LT-20
AUTOMATIC
FUNCTIONS
Stylus-lift priority: press (AV) to
reverse stylus descent. Stylus ascent
cannot be reversed before completion.
Auto lead-in: press the start (<4) button
once to commence audition.
Free travel: press (<4) and ( ®) buttons
to move the tone arm in either direction,
then (AY ) to lower it.
Auto return: the tone arm returns
automatically at the end of the disc.
Return: if, while pressing () the tone
arm moves over the edge of the disc, it
will return rapidly to rest.
Auto cut: press the stop { >) button
Once to interrupt and end disc audition.
Quick response: any movement except
lift/cue of the stylus can be interrupted
by a new command.
Free access lead-In: continue to press the
start (4) button-and the tone arm will
travel on over the disc until pressure is
released. Press the lift/cue button (a¥. }
to lower it.
Stylus protection: when there is no disc
on the platter, the stylus will not
descend, and the tone arm will return to
rest.
Repeat: pressing the repeat button turns
the repeat function alternately on and
off. When on, the indicator lights.
Lift-up and cueing: pressing the lift/cue
(4V¥) button alternately lowers and
raises the tone arm.
Manual Jead-in: first switch on the
platter
motor,
then
lift
the
stylus
over
to
the lead-in groove.
Manual lead-out: lift the stylus and
return the tone arm to the rest position.
The platter will stop automatically.
Tracking force adjustment weight
Tone arm
Arm rest/POWER switch
Head sheli
Platter mat
STOP > (Stop button)
LIFT/CUE av (Arm lift/cue button)

SPECIFICATIONS:
1. PHONO MOTOR SECTION
Drive system Direct drive
Motor
Quartz
PLL
DC
servo
motor
Platter Diameter 304mm (11-15/16”)
Weight 1.3 kg (2.9 Ibs)
Material Aluminum diecast
33-1/3, 45 rpm
0.025% (Wrms)
+0.04% Wp-p, DIN 45-507
Platter speed
Wow and Flutter
Signal to noise ratio 78 dB (DIN-B)
65 dB (IEC-B)
2. TONEARM SECTION
Type Straight type universal, static
balance
220 mm (8-11/16"’)
171 mm (6-3/4’’)
Overall length
Effective length |
Tracking error Maximum 0.1°
Head shell GFRP 6.2 g
Cartridge weight range 10—18g w/head shell
3. GENERAL
Power consumption 14W
Dimensions 424 x 142 x 417 mm
(Wx H x D) (16-3/4 x 5-5/8 x 16-3/8”’)
Weight 10 kg (22 Ibs)
Design
and
specifications
are
subject
to
change
without
notice
for
improvement.
Screws with washers(3)
LT-20 |
DISASSEMBLY INSTRUCTIONS:
1. Removal of Front Panel
1) Remove the nine screws securing the bottom cover.
2)
Remove
the
three
screws
(with
washers)
shown
in
Fig.
1.
3) The
front
panel
can
now
be
removed.
2. Removal of Tonearm Ass’y
1)
Detach
the
E-ring
and
coil
spring.
Remove
the
slit
plate
by
lifting
point
@)
slightly
upwards
and
shifting
the
plate
in the
direction
of
arrow
(Shown
in
Fig.
2).
2)
Loosen
the
wire
holder
on
the
tonearm’s
relay
P.C.B.
3)
Remove
the
two
screws
(4)
securing
the
light
receiving
P.C.B.
that
functions
to
sense
the
tonearm
position.
Take
off
the
P.C.B.
holder,
moving
it
in
the
direction
of
arrow
©.
4)
Unsolder
the
six
lead
wires
(white,
blue,
red,
green
and
two
black
from
left
to
right
in
the
figure)
leading
out
from
the
tonearm
shaft.
5) Disconnect CONN-4 of the main P.C.B. and separate it
from the other wires.
6)
After
removing
the
two
screws
@)
,
the
tonearm
ass‘y
can
be removed
by
moving
it
upwards.
7) The tonearm can now be removed from the arm base
and replaced.
NOTES
1.
Except
when
it
is
necessary
to
remove
the
tonearm’s
horizontal
movement
mechanism
©)
and
lead
wires,
them:
as
they
are.
2. When attaching the P.C.B. holder during re-assembly,
be careful not to pinch the !ead wires from the tone arm.
Front-side
are
Fig. 1
P.C.B.
holder
Slit
plate
Screws @
Wire holder Horizontal movement mechanism ©
Fig. 2
‘

A
| {
wal
“I
3. Upon completion of assembly, twist the wires leading
out: from the tonearm’s movable section to prevent.
4. After replacing the tonearm, be sure to perform tonearm
adjustments.
ADJUSTMENTS:
1. Tracking Force Adjustment
1) Set the tracking force weight to the “0” position on the
tonearm. ;
Tracking force weight
Fig. 3
2) Turn the power switch ON.
3) While lightly supporting the front of the head shell
rotate the adjustment knob for the main weight until
_ zero balance is achieved. See Fig. 4 below.
Fig. 4
4) Return the tonearm to the arm rest. Adjust the tracking
force weight to the desired weight. See Fig. 5
Set to optimum tracking weight. Fig. 5
NOTE:
Adjustments 2, 3, and 4 should always be done in sequence.
2. Tonearm Height Adjustment
1) Provide power to the unit.
2) Turn the power switch ON.
3) Loosen the arm height adjusting screw, by turning it
counterclockwise. Then, after lifting the arm holder as
high as it will go, secure it.
4) Place a (30 cm LP) record on the platter.
5) While maintaining the tonearm in the up position with
one hand, depress the <4 (START) button with the
other to lower the tonearm.
6) Turn the power switch OFF.
7) With the set in this condition, adjust the tonearm so
that it becomes level. While holding the arm holder,
position the arm pipe parallel to the record surface and
then secure it in place by turning the arm height ad-
justing screw in a clockwise direction. See Fig. 6 and 7
below.
Arm height adjustment screw
Arm holder
Fig. 6
Fig. 7
Be sure to perform adjustment 3 (Stylus Height Adjust-
ment) after completing the steps above.

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'
3. Stylus Height Adjustment
1)
After
completing
adjustment
of
the
tonearm
height,
turn
on
the
power
switch.
With
the
set
in
the
‘’Play’”’
mode,
depress
the
AW
(LIFT/CUE)
button,
which
will
cause
the
tonearm
to
be
lifted
up.
2)
The
height
obtained
at
this
point
will
be
the
stylus
height.
The
optimum
height
should
be
5
mm
(1/5")
if
it
is
other
then
this
the
Stylus
Height
Adjustment
must
be
made
using
a
hexagon
wrench.”
See
Fig.
8.
Stylus
Record Surface
5 mm
(1/5*')
_— Platter
Stylus Height
Adjustment Screw.
Hexagon Wrench
Fig. 8
* During adjustment, use care not to allow the hexagon
wrench to fall into the mechanism.
4. Arm Rest Height Adjustment
Upon completion of Tonearm and Stylus height adjust-
ments the Arm rest height must be checked as shown in
Fig. 9. If adjustment is necessary follow the steps below.
1) Loosen the arm rest height adjustment screw and move
the arm rest to the lowest position.
2) Depress the B (STOP) button and return the tonearm
to the arm rest.
3) Depress the AV (LIFT/CUE) button and lift up the
tonearm. At this point, shift the tonearm a little towards
the center spindle, and by moving the arm rest vertically,
adjust it so that there will be a clearance of 1 ~ 2mm
between the tonearm and the flat portion of the arm
rest. Secure the arm rest by tightening the arm rest
height adjustment screw.
T-20 '
Arm rest height
adjustment screw
iO
1~ 2mm
{0.04-—-0.08’’)
Fig. 9
NOTES
1) If the stylus height is too low
When the tonearm moves horizontally, the stylus will
tend to come in contact with the record surface or
platter.
2) If the stylus height is too high
Adjusted to a height decidedly higher then the proper
one, the stylus will float at low portions of a warped
record.
5. Adjustment of Lead-in Position
The cover label shown in Fig. 10 must be taken off prior
to adjusting the lead-in and rest position.
Arm rest position
adjustment screw Lead-in position adjustment screw
Fig. 10
1)
With
a
30
cm
(12”
LP)
record
placed
on
the
platter,
depress
the
<4
(START)
button
and
observe
the
lead-in
to
see
to
which
side
the
stylus
is
off-position.
2)
Turn
the
lead-in
position
adjustment
screw
a
little
using
a
screwdriver.
Depress
the
B®
(STOP)
button
and
return
the
tonearm
to
the
arm
rest.
3)
Depress
the
<4
(START)
button
and
check
the
lead-in,
position
again.
If
it is
still
improper,
repeat
Step
2).
4)
After
adjusting
the
lead-in
position
to
the
optimum
one
with
a
30
cm
record,
repeat
the
same
adjustment
with
a
17
cm
(7”)
record.

NOTES
1) Care should be used during adjustment as not to damage
the stylus as it may set down outside of the record
surface.
2) Be careful not to set the lead-in position too far inward.
This may cause improper pick-up sensing.
6. Rest Position Adjustment
* When returning the tonearm to the arm rest, if the arm
does not set properly into the notch in the arm rest
(hits either the right or left side of the arm rest during
descent), perform the following adjustments. See Fig. 11
below. ;
Correct
Fig. 11
1) Depress the <4 (START) button to cause lead-in of the
tonearm. (Watch carefully as the tonearm may fail to
perform proper lead-in.)
2) Using a screwdriver, slightly turn the arm rest position
adjustment screw.
3) Depress the B® (STOP) button to return the tonearm
to the arm rest. Confirm that the tonearm descends:
properly without touching either the right or left side
of the arm rest. If it does not descend properly into the
notch, adjust its position by repeating the above ad-
justments.
Upon completion of adjustments, confirm proper
lead-in. If the stylus fails to descend properly into the
lead-in groove, re-adjust by following the instructions
given in Adjustment 5. (Adjustment of Lead-in Posi-
tion.)
7-1 Adjustment of Horizontal Tracking Angle
1) Remove the bottom cover of the turntable.
2) Disconnect the lead wire connected to Pin 9 of the
main P.C.B. This will prevent platter rotation.
3) Disconnect CONN-4 (5 pin plug) from the main P.C.B.
4) Fig. 13 gives a detailed view of CONN-4. Push pins 3
and 5 (at Point A shown in Fig. 13) with a minus ‘S)
screwdriver and remove the lead wire.
To tonearm
Brown
UO
&
c
Orange Yellow Green
Push with minus screwdriver.
Me
A
12345
CONN -4
Fig. 12
5) Reconnect CONN-4 to the main P.C.B.
6) Connect the minus-side of an ammeter to pin 3 on the
body-side of CONN-4, and the plus-side to the orange
lead removed from CONN-4. —
7) Connect the minus-side of the other ammeter to pin 5
on the body-side of CONN-4 and the plus-side to the
green lead removed from CONN-4.
(Range: 0—100uA)
Tester 1
(Ammeter 1)
Red Orange
\
Green
Tester 2
(Ammeter 2)
Brown
Main P.C.B.
0
et
sere
Fig. 13
8) After turning on the power, depress the < (START)
button. The tonearm will be activated and decend into
the record’s lead-in groove. The tonearm will not move
further due to no platter rotation although the tracking
servo will be turned on.
9) Again turn off the power switch.
10) Disengage the drive belt for the horizontal drive motor.
11) Position the tonearm so the space ‘‘A” and ‘'B” are
equal to each other as shown in Fig. 14 below.

Tracking
adjustment screw
oy
Screwdriver
12) Read the current indicated on both the ammeters
connected in steps 6) and 7).
13) If the two current indications are not equal adjust the
Base Tracking Adjustment screw. When these two measure-
ments are equal they should be in the range of 8
to 20uA. ;
14) Disconnect the ammeters and reinsert the lead wires
Tonearm
vein)
== &) var0e
|
B to CONN-4. Reconnect CONN-4 to the main P.C.B.
7-2 Adjustment of Tracking Servo Amplifier
1) The tracking servo amplifier gain is to be adjusted
only after adjustment 7-1) has been completed.
2) Connect a DC voltmeter between Pin 12 of the main
P.C.B. and ground (Pin 10). Adjust VR101 for a
reading of 5.5 volts. Then with the voltmeter con-
nected between Pin 13 and ground adjust VR102 for
5.5 volts on the voltmeter.
After completing the adjustments apply lock-tight to
the semi-fixed resistors.
Reconnect the lead wire to Pin 9 to restore platter
operation. Re-engage the drive belt to restore horizontal
drive motor operation.
3
—
4
—
Fig. 14
Voltmeter
f
t
13126 7
CONN 4 9 8
MAIN P.C.B. Tracking Servo Amplifier Adjustment
Fig. 15

INTERNAL
DIAGRAMS
AND
PINOUT
OF
INTEGRATED
CIRCUITS:
MSA117RS
HORIZONTAL
DRIVE
I.C.
SERVO
V Ref
INPUT -B
OUT 2
COMP 2
GND 2
TC4011BP
TC9142P
x'tal
5.52960 MHz
XT XT Ni Nz CPouT 33/45 STOROBO LD Voo GND
@)
— a — — Qe
ab ope
20" 2?
Frequency
Divider
AFC B-bit
D/A Converter AFC
Frequency
Control DC Output
Lock Range
Sensing Circuit
I i t
de ae APC
aes ane Bit D/A
Converter
(7) APC
Phase Control
Frequency
Frequency Divider
Divider coats
] De Outsut
l
l
—e ee EE —
a
© yest mm

LT-20
BA6109 VERTICAL DRIVE I.C.
INPUT/OUTPUT TRUTH TABLE
FIN | R IN |Vout! |Vout 2
H
H
Lb
L
OPEN|OPEN
Vz}
Vout!
Vec2
Vout2
Vz2
O3
O2
O08
OlO
Og
Vec |
O7
6K
VR
O
4
dhe
30K 1,
FIN
O5
IK
GND
O11
1K
RINO6
oe

INFORMATION ON LOGIC IC (MSM-5831RS)
1. Circuit Construction
S-CEAD- INO tke
‘OLEAD IN
P>2Zorest
Control circuit
Input circuit
[__f>!8 ostow
{>+Dorepear- ino.
{>Lorrt prive
>_> osteo - ino.
RECORD SIZE O
2. Pin and Function
1 (S-LEAD-IN):
L when tonearm is on a record, otherwise H.
2 (S-END):
Becomes L when tonearm is moving inwards on a
record and reaches the end groove, otherwise H.
3 (S-REST):
L when at arm rest, otherwise H.
4 (UP):
L when tonearm is being tifted or moving horizontally,
otherwise H.
5 (DOWN):
L
when
tonearm
is
at
arm
rest
or
on
a
record,
otherwise
H.
6 (REPEAT):
Ordinarily
H.
When
L
is
fed
into
this
pin,
the
tonearm
continues the repeat operation. To release, feed in L
once more or make 11 (STOP) L.
7 (33/45):
Used when selecting platter speed manually. Making
this pin L causes speed to change from 33-1/3 rpm
to 45 rpm or vice versa.
9 (START), 10 (LIFT/CUE), 11 (STOP):
When START becomes L, the tonearm moves inwards;
when STOP becomes L, the tonearm moves outwards.
When LIFT/CUE becomes L, the tonearm is lifted or
lowered. Note that, while the tonearm is being lifted,
making this pin L produces no change, but if L is fed
in during sthe lowering process, it changes back to
upwards.
—10—
12 (CLK):
By connecting an external resistor/condensor combina-
tion to the input, a reference clock pulse is generated
internally.
13 (RESET):
A resistor/condensor combination is connected to the
input. Immediately after switching on the power, the
RESET input becomes L, blocking automatic move-
ment of the tonearm.
14 (Vss):
Connects to ground.
15(RECORD SIZE):
L indicates 30 cm LP, H indicates 17 cm EP.
16 (SPEED-IND):
L indicates 33-1/3 rpm, H indicates 45 rpm. Can be
changed freely by making 7 (33/45) L.
17 (T/T-DRIVE):
When 9 (START) becomes L, this pin becomes H and
the platter rotates. When record play is finished and the
returns to arm rest position, this pin becomes L and
platter rotation stops.
18 (SLOW):
To move the tonearm horizontally while on a record,
this output becomes L and the horizontal motion speed
is low. At H level, the motion speed is high.
19 (REPEAT-IND):
When 6 (REPEAT) is L in the repeat mode, this pin
becomes L.
20 (V.M-UP), 21 (V.M-DOWN), 22 (H.M-OUT), 23 (H.M-
TN):
When the tonearm is at rest position or on a record and
thus 5 (DOWN) is L, at first 20 (V.M-UP) becomes L
and the tonearm moves up, causing 5 (DOWN) to
become H. At that time 4 (UP) is L, and when the
tonearm stops at the upper limit, the horizontal motion
starts. When the tonearm moves inwards, 23 (H.M-IN)
is L, when it moves outwards, 22 (H.M-OUT) is L.
When the tonearm has moved to the pre-set horizontal
Position and is being lowered, 21 (V.M-DOWN) becomes
L. Thus, of these 4 signals during tonearm movement,
there is always one which becomes L, but never two or
more simultaneously.
27 (REST):
Same as output of 3 (S-REST).
28 (Vpp):
Supply voltage INPUT.