This extremely rare instrument was Casio's earliest midsize oriental keyboard. Although the case style is nearly a lookalike of MT-45, technically it is close to Casio MT-70 with sinewave sound engine and semi-analogue percussion.

As an arabic keyboard, the notes of the octave can be individually pitched up or down by a quartertone, which beside for arabic music is also interesting for punk-like things.

main features:

• 49 midsize keys
• built-in speaker
• 8 note polyphony (only 4 with accompaniment)
• 8 semi-OBS preset sounds {piano, pipe organ, flute, funky | vibraphone, jazz organ, tibia, chorus} selected by 4-step slider + switch
• 8 semi-OBS preset rhythms {rock, bossanova, samba, majroor, disco, swing, waltz, adani} selected by 4-step slider + switch
• accomp volume knob
• tempo knob
• fingered & single finger chord & accompaniment
• "accomp. select" switch {rhythmic, arpeggio}
• rhythm synchro & fill-in button
• vibrato switch
• sustain switch
• arabic mode (change note pitches by a quartertone)
• main & chord voice based on digital sinewave combinations, having up to 5 overtones with different digital envelopes.
• analogue percussion {base, snare, open cymbal, close cymbal, woodblock, high & low conga}
• multi-chip hardware:
• CPU= "NEC D7801G 144, 8522MX, Japan" (64 pin with strange zigzag layout)
• 2x sound IC= "Hitachi HD43517" (42 pin DIL)
• 2x DAC hybrid= "S19Z2052R 7508" (12 pin SIL)
• tuning knob
• jacks for headphone, line output

eastereggs:

• likely additional 12 preset sounds, 4 preset rhythms and switches for octave down + chord memory addable (exists in Casio AT-400).

notes:

The oriental mode is controlled by the "scale" switch. 'Normal' means off (chromatic scale). After power-on, the 'arabic' setting defaults to notes E and B lowered. To edit the tone scale, first switch to 'set'. Look at the orange marked keyboard sections. The rightmost key 'clear' resets all notes to normal (chromatic scale). Press a key in 3rd octave to lower that note by a quatertone. Press a key in 4th octave to raise that note by a quatertone. You can do this for multiple keys. But by a design flaw you can not clear individual notes (only the whole octave), so avoid to change wrong notes. Keys in octave 1 and 2 don't modify notes but can be used for play testing. Switch to 'arabic' to play music with that scale. (The changed notes affect all octaves.) You can always switch back and forth to 'normal' without loosing your setting, for hearing the difference or as a sound effect (held notes will be retriggered).

Chord uses a dull bass and organ tone (in accompaniment with sustain) that is held after key release. The accompaniment has in some patterns walking bass. When arpeggio is selected, it replaces the the staccato chord voice. Unfortunately there are no separate volume controls for rhythm, bass and chord voice.
 

This is an eBay photo of the elusive Casio AT-400. (I don't own one.) It even seems rarer than the Symphonytron.

It has 12 semi-OBS preset rhythms {rock, 16 beat, bossanova, slow rock, samba, majroor | disco, pops, swing, tango, waltz, adani}. The 20 preset sound names correspond to MT-70.

Seeing how extremely rare the AT-40 now is, it is hard to estimate how many got burnt on the stake by angry taliban. A fullsize version with more features came out as Casio AT-400 (20 preset sounds, 12 preset rhythms, woodgrain case like Casiotone 405). The only other early Casio midsize oriental keyboard is the (also very rare) Casio SK-8A. Its oriental mode can be easily retrofitted into any regular SK-8 or SK-5 as a matrix easteregg, but preset sounds and rhythms differ due to changed ROM version. Nowadays even in entry level midsize Casios a kind of oriental mode became a standard feature; e.g. the SA-80/SA-81 has 17 preset tone scales with selectable base note.
 

removal of these screws voids warranty...
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