Roland SDE-3000 Service Notes

SDE-100073000
FEB. 5,1984
PEAK HOLD & COMPARATOR (ICs 6 and 7)
The positive and negative peaks of a samped signal are peak-held and detected
at IC6 and IC7 respectively, resulting in a logic code as shown in the table
below. The code is latched into IC33 at SAH rate, passes through IC34 (data
selector) on "L" DB5 (A/D cycle), and through ICs 35C and D and reaches
pins 6 and 9 of IC10 D/A attenuator. IC10 switches ON or OFF its analog
gates to provide for correct D/A output level.
This logic code is also sent through IC33 to companding RAMs IC41 and
IC43 while A/Ded input signal data is sent from comparator IC8 to RAM
board via IC31. In other words, audio input is stored into two locations with
different information separated—meter's pointer deflection reading into IC1—
IC12 on the RAM board, and meter range into companding RAMs.
COMPANDING RAMs (IC41 and 43)
As shown in the Main Controller Timing Chart (see RAM1-RAM3) and RAM
table, A/D data for a sampled signal is stored into three RAMs (in the same
R'S section) four times starting from MSB 3 bits (D11-D9).
On the contrary, companding data is stored into IC41 and IC43 once for the
signal. However, since the same addresses are used for both RAM groups,
companding RAMs cannot make use of the remaining three addresses if suit
able modification is made on them. IC31 issues address-offset data from DBO
and DB1 to IC38 and IC36 (Address Adder) which adds 0 to 3 as the memory
banks change from RS16 to RS32, RS32 to RS48 and so on.
INPUT 100Hz
IC41 (IC43)
DIN
TP-1
1C41T1C33)
DOUT
When in delay mode (D/A cycle, IC31 DB5=H and DB6=L), companding data
is latched into IC32 on rising edge of DB4, selected by IC34 (pin 1=H), gated
by IC35C and D, then routed to IG10. With this companding data applied
IC10 determines the range of analog voltage from D/A converter IC15 and
IC14, restoring RAMs (IC1-IC12) stored data to the original signal level.
RAMs IC1-IC12 on RAM BOAHD
As mentioned earlier, during success ve approximation of a sampled signal,
comparison results are stored into th ee RAMs, being designated by RS-, in 3
bits parallel x 4 serial format to represent the signal in 12 bit data. RAMs
used for storing are always from those in RS16 (ICs 12, 8 and 4) to RS64
(ICs 9, 5 and 1) depending on delay title settings.
In short delay settings those RAMs of RS16 are repeatedly used while those
in RS64 are left out of storing. This concept becomes important when
troubleshooting RAMs. (Refer to the table on P.13).
CONTROL SIGNALS IN DIFFERENT MODES
Irrelevant to Power-ON mute sue as MUTE A and MUTE B. All "0
ing Power-ON MUTE periods.
dur
DIAGNOZING DELAY SOUND
- Isolating Defective RAM -
►For SDE-1000, see para. 5 and 6.
►Also see P.22 for failure examples.
When a trouble is found in the delay sound, the circuits first to be checked
will be those shown in the block diagram (Fig. 2, P.11).
They are closely related to each other. Of these, companding circuit effects to
both A/D and D/A conversions and the D/A converter becomes a part of A/D
converter during A/D cycle. However, the most difficult to point out is a
RAM since 14 RAMs are involved in the delay line. Consequently, this section
describes fault isolation procedure on the assumption that a specific RAM is
defective.
Before going into RAM sections, other related circuits must be checked for
proper function. These checkings also give hints for troubleshooting associ
ated circuits.
NOTE: The number of RAM cells engaged in sound delay are dependent on
delay time and the level of input signal while companding circuit acts with
changes in input sound level. Unless otherwise directed DELAY TIME should
be set at the longest and the input signal level varied widely when checking.
USE MONITOR for help checking irregular sound.
1. BRIEF CHECKING
With relatively large signal applied to the unit's input jack, observe TP-1 (IC14
pin 6); Adjust the scope to display the waveform similar to that in the photo
below.
Check steps of A/D cycle traces for 1/2-changes in voltage. If not, widely vary
the input level and check whether companding circuit is ill affecting.
When A/D conversion seems defective, proceed to para. 5.
2. DISCONNECTING COMPANDING CIRCUIT
Companding circuit affects to both A/D and D/A converters. Disconnect the
companding when checking the both circuits.
a. Disolder and remove the ground lead of R165 connecting to pin 6 of IC10.
b. Jumper wire across pin 6 of IC14 (TP-1) and pin 2 of IC8 to bypass IC10.
If companding circuit seems defective, proceed to the next para.
12

Roland SDE-3000 Specifications

General

Type	Digital Delay
Output Impedance	1 kOhm
Inputs	1/4" phone jack
Outputs	1/4" phone jack
Total Harmonic Distortion	0.05%
Power Supply	AC 117 V