Roland TR-808 Service Notes page 15

JUN.
15,
1981
DESIGN
CHANGES & IMPROVEMENTS
TR-808
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
VOICING BOARD - modification
1
MAIN
BOARD
EPT'ECTIVE
WITH
SERIAL NUMBER
PART
AFFECTED
REASON
(*
SOLUTION)
1
000300
INT
CLOCK
ICl (HD14584)
1
>0.047
Oil 0.068-^Q^Q3g
(C203)
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
2
010600 CP (Hand Clap) IC21
R346 IK
>680
R332
22K
> 27K
CP sound overmatches the rest in level.
* Reduce the gain
(Both proper and reverberation
components
.
)
3
010600 CPU
(pin 30)
R91 15K > 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
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 0 >22p
Variations in UPC4558 bias current
are transferred to l/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 amplitude.
*
Increase gain
7
010600
COMMON TRIG
IC6
(TC4011BP)
RlOl lOK > lOOK
C201 0
>22p
High frequency from CP generator induces
irregular oscillation
on
other generators
triggered at the same time.
*
Filter out CP high frequencies
8
020800
START/STOP
(IC2)
CPU
(pins
7,
31)
Q64,Q75
0 >FET
R127 0 >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
SEL2110R > TLR124
Eliminate possible chance
of
LED D76(D78)
being lit by base current
of Q5(Q2).
*
Use low sensitive LED
VOICING
BOARD
EFFECTIVE WITH
SERIAL NUMBER
PART AFFECTED REASON
(* SOLUTION)
1 000300 COW BELL
(
ICl)
Difficulty
in
setting COW BELL sound
C6 0 0 H
>0.022
frequency within
the
specified
range.
R44
39
OK >150K
R45
33
OK >100K * Extend TMl and
TM2 control range
2
010500 Q1-Q4 To have
a
clearance between Switch
2SC945P
—
>2SC2021R
Board and transistors'
top.
051850 Q
5
-Q 8
2SA733P
—
>2SA937Q
* Employ transistors
in shorter package
15