Casio CT-647 (40 songbank keyboard with unusual accompaniment)

This keyboard of 1992 employs a strange hybrid between songbank and accompaniment named "Expert Logic Accompaniment", which is a single piece that Casio didn't use in different models.

Its preset sounds and rhythms are sorted in a strange way that differes from other ToneBanks, so this is the only Casio keyboard with alphabet letter buttons. Each of the 40 built-in songs (here named "jukebox") corresponds to a preset accompaniment that can be seamlessly improvised to.

The stereo preset sounds are sample based and often more complex than in MT-750. Likely they reuse algrithms from the SA-series PCM engine softsynth for versatile modulations. Unfortunately this keyboard takes itself a bit too serious, having only establishment instrument sounds without any strange synth effect noises. There is also a keyboard drumkit mode and a simple chord sequencer.

Despite it remained unique, it was obviously no flop, since this model got re-released several times also as Casio CT-648, CTK-500, CTK-510, Concertmate 950 and Hohner PSK 41.

main features:

notes:

The case is a bit bulky but has nice speakers. The timbre quality is quite good. The "piano" is a sample, while others are mixed from waveform samples with complex modulations and panning, those sound a bit synthesized but in a positive way. E.g. the "cello" has an irregular LFO texture of vibrato and brightness changes, those may be a simulated VCF or wavetable morph effect and sounds better than a boring long loop sample. As typical for this keyboard generation, unfortunately nothing can be edited. There is only a switch for reverb (2 steps and off) but not even sustain or vibrato.

Annoying is that preset sounds often exist in only one of the 3 main groups {solo, duo, ensemble}, like when the intrusive "Expert Logic" tells you: "I am the expert here and it's solely me who decides which sounds you are allowed to combine!" The 'duo' group contains preset sound combinations with keysplit, the 'ensemble' group with layered sounds. Most are sorted such that the letter button  'A'..'H' ("bank") selects the first sound and the cipher button '1'..'5' ("number") the second. So during live play you can switch between sounds in the same row or column by one button press, which only helps when your idea of which sound should be used next matches this stubborn keyboard, else the user interface gets into your way. The 3 main groups remember each their last selected preset sound when switching among them. But a generic keysplit and layer mode (and possibly registration buttons) would have been more useful.
The accompaniments has single finger and fingered mode but refuses to play non-chords. Its AI can recognize chord progression to adapt the pattern to some kind of internal logic.

quote from manual: "The Auto-Accompaniment system of this keyboard employs a revolutionary new system that is unlike anything ever before available on an electronic keyboard. Expert Logic Accompaniment is a totally new intelligent accompaniment system that makes real-time decisions about chord progressions. Based on key judgement logic, this system automatically selects and plays the appropriate accompaniment pattern to match the key of the chord progression being played. This means it plays different patterns for the same major chord depending on whether the chord is being used as a tonic or subdominant. The result is sophisticated accompaniment patterns that are musically logical all the time."  Blah! - Sensing chord progression did Casio already in 1984 on their visionary CT-6000.

The "ad-lib musician" mode works like an Omnichord; it changes the available notes in right keyboard section to the currently played chord to enforce harmony. It can be used with the internal "jukebox" songs or normal accompaniment. quote from manual: "It adjusts the scale of the keyboard to play only the notes that match the chord being played by the accompaniment. This means you can press any key and stay within the correct scale for instant adlibs."

To properly select a song, press 'beat', a letter, a digit and then "jukebox". (If you press "jukebox" first, it starts wrong intermediate songs.) The songs are nicely made, although many have only generic names like "rock melody" or "post modern theme".

The simply chord sequencer can record and playback your chord track in realtime. It has no edit and gets deleted by (auto-) power off.
 

hardware details

The Casio CT-647 is built around the CPU "OKI M6566B-03" (crystal clocked at 43.45 MHz) with external 256KB ROM.
This hardware description is based on the service manual of Casio CTK-500, which has a different CPU name "MSM6626-01GS-K-108" (aka "M6626" in schematics; both are 80 pin SMD in same package) but same ROM "MN232000CUQ" (40 pin DIL) and also songs and rhythms are the same, so I expect that both models are very similar.

Internals of the accompaniment AI algorithm for chord progression are described in patent US4896576 and US5510572.

keyboard matrix

This keyboard matrix is based on the Casio CTK-500 service manual. It seems very close to CT-647 athough the CPU name (but not ROM) differs. I expect that the matrix is the same. I haven't analyzed it by myself, so there may be unknown eastereggs.
 
KI0
KI1
KI2
KI3
KI4
KI5
KI6
KI7
 
CPU pin
in 0
in 1
in 2
in 3
in 4
in 5
in 6
in 7
in / out
 
o
C2
o
C#2
o
D2
o
D#2
o
E2
o
F2
 
 
out 0
KO0
o
F#2
o
G2
o
G#2
o
A2
o
A#2
o
B2
 
 
out 1
 KO1
o
C3
o
C#3
o
D3
o
D#3
o
E3
o
F3
 
 
out 2
 KO2
o
F#3
o
G3
o
G#3
o
A3
o
A#3
o
B3
 
 
out 3
 KO3
o
C4
o
C#4
o
D4
o
D#4
o
E4
o
F4
 
 
out 4
 KO4
o
F#4
o
G4
o
G#4
o
A4
o
A#4
o
B4
 
 
out 5
 KO5
o
C5
o
C#5
o
D5
o
D#5
o
E5
o
F5
 
 
out 6
 KO6
o
F#5
o
G5
o
G#5
o
A5
o
A#5
o
B5
 
 
out 7
 KO7
o
C6
o
C#6
o
D6
o
D#6
o
E6
o
F6
 
 
out 8
 KO8
o
F#6
o
G6
o
G#6
o
A6
o
A#6
o
B6
 
 
out 9
 KO9
o
C7 
 
 
 
tempo
+
tempo
-
 
 
out 10
 KO10
power off
C.
off
C.
fingered
C.
single finger
 
 
 
 
out 11
 KO11
accomp volume 1
accomp volume 2
accomp volume 3
accomp volume 4
accomp volume 5
      
out 12
KO12
reverb
off
reverb
1
reverb
2
          
out 13
KO13
R.
synchro/
fill-in
R.
start/stop
R.
intro/ending
S.
memory
record
S.
memory
play
ad-lib musician
jukebox
start/stop
R.
beat
out 14
KO14
N.
'A'
N.
'B'
N.
'C'
N.
'D'
N.
'E'
N.
'F'
N.
'G'
N.
'H'
out 15
KO15
N.
'1'
N.
'2'
N.
'3'
N.
'4'
N.
'5'
O.
solo
O.
duo
O.
ensemble
out 16
KO16

The input lines are active-high, i.e. react on +Vs. Any functions can be triggered by a non- locking switch in series to a diode from one "out" to one "in" pin.
 

legend:
"o"
 = keyboard key
underlined
 = function needs locking switch (i.e. stays active only so long the switch is closed)
R.
 = preset rhythm
O.
 = preset sound ('orchestra')
C.
 = chord
S.
 = sequencer
N.
 = number/letter button
orange
background		 = easteregg (unconnected feature)
grey
background		 = unconnected doublet

The panel LEDs are latched by a TC74CH174AP from CPU pins KO0..KO5 during a pulse on KO17.

pinout M6566B(?), M6626

The CPU "OKI M6566B-03" (80 pin SMD) is the CPU of Casio CTK-647. The "OKI M6626-01GS" (80 pin SMD) is the CPU of the almost identical CTK-500 and looks like a minor variant of it. (Confirmed by Revenant, who dumped the external CT-647 ROM. The -03 and -01 are software numbers of internal ROM.) No much is known about this chip, beside it contains 16-note polyphonic PCM sound generation with internal stereo DAC and external ROM. Likely it runs a versatile softsynth like in earlier Casio PCM keyboards (see SA-series).

This pinout is based on the Casio CTK-500 service manual, which has a pinout of "OKI M6626-01GS" and schematics drawing.
 
pin name purpose
1 KO7 key matrix out
2 KO8 key matrix out
3 KO9 key matrix out
4 KO10 key matrix out
5 KO11 key matrix out
6 KO12 key matrix out
7 KO13 key matrix out
8 KO14 key matrix out
9 KO15 key matrix out
10 KO16 key matrix out
11 KO17 led latch clock out
12 KO18 APO auto-power-off out
13 KO20 (not used)
14 KI0 key matrix in
15 KI1 key matrix in
16 KI2 key matrix in
17 KI3 key matrix in
18 KI4 key matrix in
19 KI5 key matrix in
20 KI6 key matrix in
21 KI7 key matrix in
22 /MI power-on trigger in
23 /reset reset
24 REFH dac low reference voltage (capacitor to AGND)
25 AVDD dac supply voltage +5V
26 ROUT right audio out
27 LOUT left audio out
28 AGND dac ground 0V
29 REFL dac high reference voltage (capacitor to AGND)
30 TEST2 (wired to GND)
31 TEST1 (wired to GND)
32 GND ground 0V
33 COSI clock in (43.45 MHz)
34 COSO clock out
35 VDD supply voltage +5V (always on)
36 /CE chip enable
37 /OE read enable
38 ADR19 (not used)
39 ADR18 (not used)
40 ADR17 (not used)
pin name purpose
41 ADR16 rom address bus
42 ADR15 rom address bus
43 ADR14 rom address bus
44 ADR13 rom address bus
45 ADR12 rom address bus
46 ADR11 rom address bus
47 ADR10 rom address bus
48 ADR9 rom address bus
49 ADR8 rom address bus
50 ADR7 rom address bus
51 ADR6 rom address bus
52 ADR5 rom address bus
53 ADR4 rom address bus
54 ADR3 rom address bus
55 ADR2 rom address bus
56 ADR1 rom address bus
57 ADR0 rom address bus
58 DIN15 rom data in
59 DIN14 rom data in
60 DIN13 rom data in
61 DIN12 rom data in
62 DIN11 rom data in
63 DIN10 rom data in
64 DIN9 rom data in
65 DIN8 rom data in
66 DIN7 rom data in
67 DIN6 rom data in
68 DIN5 rom data in
69 DIN4 rom data in
70 DIN3 rom data in
71 DIN2 rom data in
72 DIN1 rom data in
73 DIN0 rom data in
74 KO0 key/led matrix out
75 KO1 key/led matrix out
76 KO2 key/led matrix out
77 KO3 key/led matrix out
78 KO4 key/led matrix out
79 KO5 key/led matrix out
80 KO6 key matrix out

The external ROM address and data lines are wired 1:1 to the CPU pins of corresponding name.

A CT-647 with changed case design and built-in CD-player came out as Casio KT-80 and in Japan with CD+G player as KT-90G. But Casio never made real variants with diffferent songs or other software changes. Possibly the way how in its chord AI songs and accompaniments got tightly intertwined (perhaps as terrible handwritten spaghetti code) made song replacement and bugfixing prohibitively costly, so Expert Logic Accompaniment remained a singleton.

Now in an age where cloud based AI has begun to analyze and produce entire songs with singing, all instruments and video of the imaginary band, it became just a historical artefact, that like chess computers witnesses of a time where AI was less science than fiction. Fortunately this keyboard is clever, not smart - offline and 100% app-free it will keep working even after all cloud services have been shutdown.
 

 removal of these screws voids warranty...    
WarrantyVoid
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