Design Changes - Roland TR-808 Service Notes

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