JUN.
15,
1981
DESIGN CHANGES 8e
IMPROVEMENTS
The
reasons
for modifications will
help to remedy the
problems
as
described
below, may be found
on early
TR-808
.
Some of the modifications
were
done
at
the
factory on some products
bearing serial
number
earlier than indicated:
MAIN
BOARD
-
modification
1,
4
VOICIN(}
BOARD
-
modification 1
MAIN BOARD
TR-808
EPPECTIVE
WITH
SERIAL
NUMBER
PART
AFFECTED
REASON
(*
SOLUTION)
1
000300
INT CLOCK
ICI (HD14584)
Variations
in HD14584
hysterisis
sometimes
deviate Clock
Rate out of
specified frequency
range.
*
To down
-
0.047+0.039
in parallel
*
To up
-
remove
0.039
Cll
0.068-
(C203)
2
010600 CP
(Hand Clap) IC21
R346
IK
>
680
CP
sound
overmatches the
rest in
level.
*
Reduce
the gain
(Both
proper
and reverberation
components
.
)
iVjj^
^^Iv
^
iL 1
K
3
010600 CPU
(pin
30)
"P01
1
'^V ^IM
Small
resistance allows CPU
to draw
relatively larger current from back-
up
batteries
with
MODE
selected
other
than
PLAY
or
MANUAL
PLAY
in Power
OFF.
*
Increase
resistance
IX
y
J-
±Ji\.
-*
-LH
4
010600
DIN
SOCKET
(pin
5)
R25
220K
>1.5M
Reject unnecessary signals
from
external circuitry to prevent false
triggering at subsequent stage.
*
Increase resistance
CPU
(pin
37)
Capacitor 0.01 across
DIN pin 2
and chassis
Grounding
Protect CPU
against static
electricity
build-up at external circuitry.
*
By
pass
charge
5
010600 NOISE GENERATOR (IC24)
R129 330K
>
short
R311 330K >100K
R127
4.7K->10u(C200)
C202
>22p
Variations
in
UPC4558 bias current
are transferred to
1/2
IC24
output as
an offset
reducing gain margin.
"^
Decouple DC
MAIN
BOARD
cont'd
EFFECTIVE WITH
SERIAL NUMBER
PART AFFECTED
REASON
(*
SOLUTION)
6
010600
VOICE GATE
R106, 1^154, R182,
R213
,
R242, R268, R298
22K
>
lOK
Ensure
sufficiency
of gate drive signal
voltage at lower COMMON TRIG
amiplitude.
*
Increase gain
7
010600
COMMON TRIG
IC6
(TC4011BP)
High frequency
from CP generator induces
irregular oscillation on other
generators
triggered at the same time.
*
Filter
out
CP
high frequencies
-l1_LUX -LUiV
y>
±UUlv
C201
>22p
8
020800
START/STOP
(IC2)
CPU (pins
7,
31)
Q64,Q75
>FET
R127 >6.8K
R54 IM >100K
D32
1
>0
Prevent possible disturbance in
RAM
memories at power on/off switchings
with MODE
set at other than
PLAY
or
MANUAL
PLAY.
*
Add
PET
switches
9
031100
LED
OTTiT
o
-]
-]
p,rj
N TT T?
1
'^i
'1
Eliminate
possible
chance of
LED D76(D78)
being
lit by base current
of
Q5(Q2).
*
Use low sensitive
LED
ioJi-U^_LJ.U-Lt > ±-ljiL±(^'-|-
VOICING
BOARD
EFFECTIVE
WITH
SERIAL
NUMBER
PART AFFECTED
REASON
{*
SOLUTION)
1
000300 COW
BELL
(ICI)
C6
0.01
>0.022
R44
390K >150K
n /
rr -F -z r\Tr •^
-\
r\r\j7-
Difficulty
in
setting
COW
BELL
sound
frequency
within
the
specified range.
^
Extend TMl
and
TM2
control range
2
010500
Q1-Q4
To
have
a
clearance
between Switch
Board
and
transistors' top.
*
Employ
transistors in shorter package
tLyJ^\ji\-'ji. ^ ^0"^<^U^J-iL
051850
Q5-Q8
i^)OJ±ljjL
^
^uA)jj
IW.
15
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