Noise is the result of improperly trimmed DAC (digital / analog converter).

• Open the top cover of JD-990.
• With the JD turned off, hold down INC + DEC buttons then turn power on.
• This should get you into the test mode.
• Then press UTILITY + F3. This gets you into the MSB Adjustment page.
• Make sure the volume control is at maximum. (Watch out you speakers!)
• Press the value knob, a 440hz sine-wave is produced.
• Use an instrument such as an oscilloscope to observe the output waveform. If you don’t have oscilloscope, you can use headphones and listen carefully with your ears.
• Adjust VR1 to obtain a smooth sine wave.
• The VR1 is located on the main board, top right side of it (if JD is placed with its front side facing you). In fact it is the only trimmer potentiometer there.

Problems solved by various JD-990 OS versions

Ver 1.03 for the JD-990
-----------------------
1. In the perfomance mode , when a patch with " structure / sync `
is assigned to plural Parts and it is played , the sounding way get
wrong gradually and then the JD-990 may hang up at last.

2. JD-990 may hang up when the JD-990 receives Program Change
message from an external MIDI device during playing .

3. In case that " Atari Cubase " is used with JD-990 , the JD-990
hangs up when the Cubase is booted up .

4. JD-990 may hang up when you change/edit a patch during playing
in the Performance mode.

5. JD-990 outputs some wrong data after the JD-990 receives " RQ1 "
of " Performance Temporary Patch " .

6. When " Performance Temporary Patch " is send back to the JD-990,
the " Effect " sound may be changed .

7. JD-990 hangs up when the JD-990 recieves a large amount of System
Exclusive data during " Demo Play " .

8. When JD-990 plays A3 ( Claves ) by Rhythm Set of SL-JD80-02


Ver 1.04 for the JD-990
-----------------------
1. JD-990 may hang up or return to the factory presets when the JD-
990 reseives big MIDI data at short time during playing.


Ver 1.05 for the JD-990
-----------------------
1. Even set the Tone delay time to 5.0 sec. In Patch / WG , the
delay time would be about 3 sec. This only occurs with Ver 1.03 and
1.04 .

2. When load a patch of JV-series , the rate of S&H/ Random LFO
will be delayed.

* In Ver 1.05 , the following have been improved.

1. An algorithm of Chorus and Reverb have been adjusted to have
more compatibility with JV's patch. The nuance was different in case
with previous version.