CASIO CT-840   lo-fi wavetable keyboard with ROM-Pack & key lighting DO.RE.MI.GUIDE
Casio MA-220

Casio CT-840

This keyboard from 1992 (embossed case date) has almost the same sound generator like Casio MA-130, but additionally a key lighting feature ("melody guide") with music stored on ROM-Pack cartridges. The CT-840 was apparently Casio's last big keyboard with ROM-Pack feature.
Like MA-130, the CT-840 has the same great 100 lo-fi wavetable sounds and rhythms, but instead of the "poly/ texture" button it has a "tone mix" (dual voice) button to layer any 2 preset sounds. Additionally there are 5 responsive rubber drumpad buttons (switchable to 5 effect sounds) and a feature called "DO. RE. MI. Guide", which sings the main voice in a low resolution sample child voice (only monophonic). Important to mention is that despite many false claims this function has absolutely nothing to do with the sing input features found on Casio VA-10; the microphone jack of CT-840 is only output through the analogue amplifier and has no means of digital sound control or sampling. A benefit of this hardware class is that it is still based on the great SA-series sound engine, but buttons presses here sound no noises and thus won't disturb live performance.

Unlike modern key lighting keyboards, not the keys itself but a row of tiny LEDs above the keys flash up to teach keyboard playing, but here the LEDs are placed like musical notes on note lines to show which key belongs to which note. In opposite to earlier ROM-Pack keyboards it has not only a melody guide, but also a chord training feature, that teaches to play fingered chords.

main features:

Casio CT-840 JASRAC, T-150340, CT-840

eastereggs:

  • 12 higher note keys addable (but highest 4 garble timbres).

    • notes:

    The rastered volume control is annoying, since the lowest volume is often too quiet, while the 2nd is already too loud. Annoying is also that the LCD can not display the actual tempo setting and that there are no separate volume controls for rhythm and accompaniment. The given accompaniment volume slider has only 3 volume steps and off, and it responds a little slow. Most interesting is for me that this instrument can play ROM- Pack cartridge music through its 100 ToneBank PCM sound engine, although the semi- analogue Casio MT-800 sounds much warmer and nicer here. Due to the ROM- Pack standard is older than the 100 ToneBank technology, ROM- Pack musics itself still can select only from each 12 particular preset sounds and rhythms. Strange is that these 12 preset rhythms are marked with an asterisk in the rhythm list on the control panel, while the 12 preset sounds have none. The internal speaker has enough bass but sounds slightly dull.

    The sound of this instrument is almost identical with Casio MA-130 (see there) but instead of the "poly/ texture" button there is a "tone mix" button to layer any 2 preset sounds, since the tone generator apparently has doubled internal polyphony. Also the "piano" sound is more natural with higher resolution and noticeable sampled attack phase. (I prefer the MA-130/ SA-series piano.) The fact that Casio omitted in this hardware the annoying button press click noise shows that it was either considered a more professional "non-toy" model or that Casio thought the LCD (which is absent in cheaper variants) will be sufficient to confirm button presses.

    The "DO. RE. MI. Guide" button replaces the melody voice (also with demos etc.) with a monophonic Japanese child voice that sings the note names {"do"," re", "mi", "fa", "so", "la", "si", "do"}. Unlike MC-32, this one sings the correct pitch in the whole melody section of the keyboard and only repeats a higher octave in the octave below. Also sharps (black keys) are sung, although as note names of the corresponding naturals. The voice sings quite Engrish "le" instead of "re". The sung note is played only about 1 second long, but is truncated with even shorter note. I am not sure if this bombastically advertised hype feature really helps much with learning notes. At least the low resolution sample quality of the voice is very noisy and thus makes a nice sound effect; unfortunately it can play only monophonic.

    The rhythm and accompaniment is also very similar like MA-130 (grainy lo-fi samples) with the only difference that here there is also a manual chord mode (pipe organ timbre) with rhythm off. Unfortunately it plays nothing else than standard establishment chords and stubbornly ignores any other key presses even in fingered chord mode. When new keys are pressed in the chord section, it always stops the organ chord tone for a fraction of a second, even when the new key combination continues with the same chord. (This can be also used as a sound effect.)

    The 5 drumpads are very responsive and play 5 sound effects after power-on. The "phone bell" rings like a mechanical one so long the pad is held. The "laser beam" corresponds to the 3rd keyboard section of the same preset sound. The "bird tweet" is a high short synth whistle with falling pitch, the "siren 1" resembles a synth tom with falling pitch, while "siren 2" howls up with strong and fast vibrato. (Names were chosen by me since the control panel only shows icons.) The "metronome" button replaces the current rhythm with a metronome made from low and high clicking clave sounds (high for first beat of a bar, low for the others), which makes also a nice alternative rhythm, since it can be combined with the given accompaniments and toggled back and forward during running accompaniment.

    The chord sequencer is fairly complex but has no permanent memory and thus looses its data by power-off and even auto-power-off, which is a severe design flaw considering the effort Casio has put into this feature.

    The "melody guide" key lighting feature can use as well the 5 built-in demo musics as external ROM- Pack cartridges, and you can even play their music with any of the 100 preset sounds & rhythms by switching them in between (although the programmed music may switch them back). The built-in musics are selected when no cartridge is inserted. The song "DO-RE-MI" always starts with "DO. RE. MI. Guide" enabled, thus singing its notes. Beside the melody voice, you can even train fingered chord play with this instrument, a feature that was likely introduced first with Casio MT-820 and MT-88.
     

    hardware details

    Despite same sound and rhythm set like Casio MA-130, the CT-840 has instead of the classic SA-series CPU M6387 an "OKI M6567-04" with 80 pins.

    A bit strange is that there is an unused section with empty holes on the amp PCB; possibly originally a different microphone amplifier was planned here and then left blank to circumvent a PCB design flaw; the given mic amp seems to be mounted on a small daughterboard instead. The key leds are demultiplexed by 2 octal latch logic ICs 74HC373AP.
    Due to messy hardware with many small PCBs on short cables and a flimsy LCD foil cable I didn't dare to analyze the CT-840 further. Instead I analyzed its mechanically simpler variant Casio MA-220, thus for keyboard matrix and circuit-bending details see there.

    pinout M6567

    The "OKI M6567-xx" CPU (pins count anticlockwise, xx = software number of internal ROM) is a 80 pin SMD variant of the M6387 that (unlike older Casio keyboards) supports a matrix of key lighting LEDs without driver transistors. Each LED is likely wired from an LEDY to an LEDX pin; the led groups need to be demultiplexed by 2 octal latch logic ICs (74HC373AP). Pins 13..27 seem to control the LCD. The pins 65..72 can control a ROM-Pack port. Without a ROM-Pack connected, the key lighting uses (demo) songs from its internal ROM. Unlike M6387 it supports a larger key matrix (up to 61 keys) and has more internal ROM, which is used for additional samples (piano timbre, "DO. RE. ME. Guide") and SongBank (apparently up to 64 songs). Due to 16 note polyphony it is clocked twice as high (43.45 MHz, turns slightly warm). But despite improvements this is still an entry level keyboard CPU with neither stereo nor midi support. The non-persistent chord memory in CT-840 suggests that this CPU contains no SRAM and disables DRAM refresh during standby to conserve batteries.

    The versions of "OKI M6567-xx" ("xx" = software number of internal ROM) seem to differ mainly in the count of internal demo songs and supported keyboard length. (Likely all versions can poll 61 keys, although most instruments have only 49; e.g. in MA-220 keys above 57 distort.) In later software versions (likely all with >15 song, selected through cipher buttons) all 61 keys work, but many features were removed to save rom space for more melodies and partly more or higher resolution samples. So CTK-200 (software number 11) lacks melody guide modes, ROM-Pack support, DoReMe-Guide and even the drumpad samples were omitted (silent, but still mute rhythm for 1 bar, one pad sounds a piano note). These all have a changed preset sound set (boring) with more sample based preset sounds. The preset rhythm set (at least their order or names) varies among later variants. CTK-450 has technically 64 songs (32 of them "free sessions") but only 8 cipher buttons for its 64 sounds and rhythms, so likely others were omitted to save rom space. (It is unknown if the 2 omitted cipher buttons access some of them as eastereggs.) 
     
    software number hardware class notes & features
    04 CT-840 5 songs, key lighting, lcd, 49 keys (up to 57 work)
    05 MA-220 15 songs (rest behaves like 04)
    ? CTK-150 30 songs, melody on/off button, (seen on eBay)
    11 CTK-200 40 songs, melody on/off button, 61 keys work, broken drumpad support
    ? CTK-300 dto. with drumpads
    15 CTK-450 32 songs + 32 free sessions (= technically 64 songs), 61 keys, melody on/off button, only 64 sounds & rhythms, has 8 cipher buttons
    16 CTK-450 dto. (bugfix release?, '15' crossed out in schematics)

    This pinout was concluded from the service manuals of Casio CTK-450 (has neither ROM-Pack nor key LEDs, 32 song bank, CPU="OKI M6567-15"), ML-2 and SK-8.
     
    pin name purpose
    1 LEDY7 led matrix out
    2 LVDD1 led supply voltage +5V
    3 LGND2 led ground
    4 LEDX0 led matrix out
    5 LEDX1 led matrix out
    6 LEDX2 led matrix out
    7 LEDX3 led matrix out
    8 LEDX4 led matrix out (in MA-220: tone/beat select button led, in CTK-200: melody on/off button led)
    9 LEDX5 led matrix out (in MA-220, CTK-200: tempo led)
    10 LEDX6 led matrix out | auto-power-off APO out
    11 LEDX7 led matrix out
    12 LVDD2 led supply voltage +5V
    13 CMZ lcd out
    14 CMY lcd out
    15 CMX lcd out
    16 SA1 lcd out
    17 SA2 lcd out
    18 SA3 lcd out
    19 SA4 lcd out
    20 SB1 lcd out
    21 SB2 lcd out
    22 SB3 lcd out
    23 SB4 lcd out
    24 SC1 lcd out
    25 SC2 lcd out
    26 SC3 lcd out
    27 SC4 lcd out (in CTK-450: 55.25 Hz)
    28 GND2 ground
    29 COSI crystal in | clock in (43.45 MHz)
    30 COSO crystal out
    31 VDD supply voltage +5V (in CTK-450: 5.8V)
    32 GND2 ground
    33 TEST1 (wired to GND2) | ?
    34 TEST2 (wired to GND2) | ?
    35 TEST3 (wired to GND2) | ?
    36 MI (not used)
    37 -RESET reset
    38 AVDD analogue supply voltage +5V (filtered)
    39 OUT sound out
    40 AGND analogue ground
    pin name purpose
    41 KI0 key matrix in
    42 KI1 key matrix in
    43 KI2 key matrix in
    44 KI3 key matrix in
    45 KI4 key matrix in
    46 KI5 key matrix in
    47 KI6 key matrix in
    48 KI7 key matrix in
    49 KO0 key matrix out
    50 KO1 key matrix out
    51 KO2 key matrix out
    52 KO3 key matrix out
    53 KO4 key matrix out
    54 KO5 key matrix out
    55 KO6 key matrix out
    56 KO7 key matrix out
    57 KO8 key matrix out
    58 KO9 key matrix out
    59 KO10 key matrix out
    60 KO11 key matrix out
    61 KO12 key matrix out
    62 KO13 key matrix out
    63 KO14 key matrix out
    64 KO15 key matrix out | NC (hi)
    65 CE rom pack enable
    66 PC1 rom pack clock1
    67 PC2 rom pack clock2
    68 OP rom pack /address data
    69 D0 rom pack bus
    70 D1 rom pack bus
    71 D2 rom pack bus
    72 D3 rom pack bus
    73 LGND1 led ground
    74 LEDY0 led matrix out
    75 LEDY1 led matrix out
    76 LEDY2 led matrix out
    77 LEDY3 led matrix out
    78 LEDY4 led matrix out
    79 LEDY5 led matrix out
    80 LEDY6 led matrix out

    The pins are arranged in a way that in simple instruments (no ROM-Pack, key lighting, lcd) many adjacent pins can be left unused to ease PCB layout.

    In MA-220 pin 36 seems to output a HF clock signal, that is too fast to see on my analogue oscilloscope. Its ROM-Pack port pins output a short lo-pulse only before a demo song starts, so it likely polls for ROM-Pack presence and then turns the port off, which doesn't seem to be connected with an internal bus. Pin 64 stays hi and thus is not keyboard matrix output. The LCD output waveform has 4 voltage steps.

    In CTK-200 pin 8 is the unused 'Melody on/off' button LED (off=hi). Despite it supports no key lighting modes, during songs pins 4..7 and 74..80 still output multiplexed key led signals (pin 11 stays lo). Also the lcd port (pin 13..27) is still alive and changes with selected chord or numbers. But the ROM-Pack port (pin 65..72) always stays hi (also during song selection), thus support was likely removed to save rom space.

    Strange is that both in MA-220 and CTK-200 the unused CPU pins 1, 4..7, 11..26, 65..72, 74..80 (led, lcd and rom pack port) are wired to empty solder pads, but not e.g. the likewise unused pin 58. This suggests that only those with solder pads were important for factory tests and so e.g. may be suited to access internal ROM or RAM contents through a hidden test mode.

    Smaller 100 ToneBank instruments with ROM- Pack slot and 5 drumpads were the mini keyboard Casio PT-88 and its midsize variant PT-380. The oldest (and most noble sounding) ROM-Pack keyboard was Casio MT-800.

    Casio MA-220

    This keyboard from 1992 (embossed case date) is basically a cheap midsize variant of Casio CT-840. Instead of ROM-Pack slot and key lighting it has only a SongBank of 15 built-in demo tunes.

    It can be considered a slightly higher grade variant of MA-130 with 2 speakers, additional drumpads, simple chord sequencer and manual chord mode.

    different main features:

    eastereggs:

  • likely all features of CT-840 addable.
  • 12 higher note keys addable (but highest 4 garble timbres).

    • notes:

    The 2 speakers have less bass than CT-840 but enough treble. Unfortunately there is some static digital noise (keyboard matrix beep, LED switching) in the background.
     

    circuit bending details

    The Casio MA-220 is based on the single-chip CPU "OKI M6567-05", which except different demos seems identical with the "M6567-04" of CT-840. The op-amp "XRAI 5218" (PCB label M5218APR) seems to be used as a noise gate (concluded from CTK-450 service manual) to fight static digital noise - by lack of proper shielding without much success. The power amp is a "Casio LA5668N, 284" (10 pin SIL).
    Like MA-130 the case has lots of screws, but the rest is straight forward and easy to dismantle.

    keyboard matrix

    The pinout of the 15 pin ribbon cable JA (counting right to left) is:

    KI2, KI3, KI4, KI5, KI6, KI7, KO2, KO4, KO5, KO6, KO7, KO8, KO3, KO1, KO0

    KI0 is on the 2nd diode of the horizontal diode row in the middle of the PCB. KI1 is at the 3 diodes with the "9" near the 'mode' slide switch. KO9..14 are accessible on the PCB back at corresponding panel button contacts and KO9 only as unused CPU pin.

    I examined this keyboard matrix by myself, based on the Casio CTK-450 service manual. Missing and different functions were concluded from behaviour of my CT-840, which matrix seems identical, so there are tons of eastereggs.
     
    41 KI0
    42 KI1
    43 KI2
    44 KI3
    45 KI4
    46 KI5
    47 KI6
    48 KI7
     
    CPU pin
    in 0
    in 1
    in 2
    in 3
    in 4
    in 5
    in 6
    in 7
    in / out
     
     
    M.
    power off
    o
    C2
    o
    C#2
    o
    D2
    o
    D#2
    o
    E2
    o
    F2
    out 0
    49 KO0
     
    M.
    play
    o
    F#2
    o
    G2
    o
    G#2
    o
    A2
    o
    A#2
    o
    B2
    out 1
    50 KO1
     
    M.
    fingered
    o
    C3
    o
    C#3
    o
    D3
    o
    D#3
    o
    E3
    o
    F3
    out 2
    51 KO2
     
     M.
    single finger
     o
    F#3
     o
    G3
    o
    G#3
    o
    A3
    o
    A#3
    o
    B3
    out 3
    52 KO3
     
     M.
    song
    o
    C4
    o
    C#4
    o
    D4
    o
    D#4
    o
    E4
    o
    F4
    out 4
    53 KO4
     
    G.
    autoplay
    o
    F#4
    o
    G4
    o
    G#4
    o
    A4
    o
    A#4
    o
    B4
    out 5
    54 KO5
     
    G.
    any key play
    o
    C5
    o
    C#5
    o
    D5
    o
    D#5
    o
    E5
    o
    F5
    out 6
    55 KO6
     
    G.
    melody guide 1
    o
    F#5
    o
    G5
    o
    G#5
    o
    A5
    o
    A#5
    o
    B5
    out 7
    56 KO7
     
    G.
    melody guide 2
    o
    C6
    o
    C#6
    o
    D6
    o
    D#6 
    o
    E6
    o
    F6
    out 8
    57 KO8
     
    G.
    freeplay
    o
    F#6
    o
    G6
    o
    G#6
    o
    A6*
    o
    A#6*
    o
    B6*
    out 19
    58 KO9
     
    DoReMi
    Guide 
    o
    C7*
    N.
    4
    N.
    3
    N.
    2
    N.
    1
    N.
    0
    out 10
    59 KO10
    tempo
    -
    accomp.
    volume 1
    (mute)
    R.
    hihat loop
    N.
    9
    N.
    8
    N.
    7
    N.
    6
    N.
    5
    out 11
    60 KO11
    tempo
    +
    accomp.
    volume 2
    R.
    metronome
    tone mix
    C.
    chord form
    C.
    step record
    C.
    record
    C.
    play
    out 12
    61 KO12
     
    accomp.
    volume 3
    R.
    hihat loop
     
    rhythm/ sound
    select
    R.
    metronome
    R.
    start/ stop
    R.
    sync/ fill-in
    out 13
    62 KO13
     
    accomp.
    volume 4
    P.
    variation
    P.
    2
    (lo syntom)
    P.
    1
    (base)
    P.
    3
    (hi syntom)
    P.
    5
    (cymbal)
    P.
    4
    (snare)
    out 14
    63 KO14

    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
    R.
    		 = preset rhythm
    C.
    		 = chord sequencer
    P.
    		 = drumpad
    N.
    		 = number entry (cipher buttons)
    M.
    		 = mode select switch
    G.
    		 = 'melody guide' switch
    orange
    background     		 = easteregg (unconnected feature)
    grey 
    background    		 = unconnected doublet

    • higher note keys & garbled timbres
      12 additional higher note keys can be added, but the highest 4 of them play wrong pitch or sound chopped distorted (depending on preset sound), which can be used as a sound effect.
      Likely an internal pitch lookup table is too short or the internal octave setting is too high for the synthesis engine. In Casio MT-88 I found similar high octave glitches when fixed diodes are set into modes for shorter keyboards, but in MA-220 I found no fixed diodes or their matrix places (which doesn't mean that they don't exist - they are hard to identify).
      The Casio CTK-450 (seen in service manual) has real 61 keys (certainly without glitch) and no fixed diodes. Its keyboard matrix is very similar, but with separate 'tone' (KO13->KI3) and 'rhythm' (KO13->KI4) buttons and a 'melody on/off' toggle button (KO13->KI5) instead of using 2 matrix places. Because Casio service manuals only show the currently used functions, it is hard to estimate how different it is.
      The additional keys don't select additional demo songs.
    • DO.RE.MI-Guide
      A button at KO10->KI1 toggles the main voice into a grainy monophonic lofi sample voice that sings the note names of each key.
    • metronome
      A button at KO13->KI5 or KO12->KI2 toggles the rhythm track into a metronome.
    • melody guide
      The "melody guide" slide switch was intended for key lighting keyboards. The MA-220 lacks key leds and only employs 2 of the 5 available modes, i.e. "any key play" (melody on) and "melody guide 2" (melody off). The other 3 modes are KO6->KI1 ("any key play" = any keys step through melody), KO7->KI1 ("melody guide 1" = wait for correct key) and KO9->KI1 ("freeplay" = melody off + chord off, i.e. only rhythm + obligato).
    • step record
      A button at KO12->KI5 enters a chord into the "chord memory" sequencer. Press it as many times as the number of beats you want to enter. The chord type can be selected with the number buttons; use "delete" to remove the last chord.
       
      m
      7
      M7
      sus4
      dim
      aug
      6
      9
      -5
      delete
      0
      1
      2
      3
      4
      5
      6
      7
      8
      9
    • chord form
      This mode is useless without LCD and key leds. A button at KO12->KI4 toggles into a kind of chord dictionary mode. Playing a single finger chord and selecting a chord type with number buttons (see above) will display the correct fingering of that chord on key leds.
    • strange mode (hihat loop)
      A button at KO13->KI2 or KO11->KI2 enters a strange mode that plays a hihat beat (like a metronome). It activates fingered chord but mutes the chord section and disables cipher buttons. Only keys, tempo and drumpads work. When metronome was on, it will mix into the hihat beat, but the metronome button doesn't work. Press start/stop to exit this strange mode.

      I am not sure what this was intended for. It may be only a test mode (pressing the button again immediately restarts that beat at the 'one', which sounds crude), but it also may be a record mode of some kind of sequencer (like a "custom drummer") that I didn't get to work. Possibly it is just dead code left over from something else. The hihat beat with muted chord section may be related to the lead-in condition before starting a demo or rompack song; also here only keys and drumpads work and chord section is mute. The only difference is that the 'beat/tone' button toggles its led, while the strange mode doesn't.

    Different from this, apparently all M6567 based instruments with more than 15 songs select them through cipher buttons (entering 2 digit numbers) instead of individual keys and so have a changed matrix layout like Casio CTK-200 with fewer eastereggs.

    The instrument has 15 nicely arranged demo melodies, those main voice can be muted with the 'song melody' switch (which exits the song). The melodies are:

    1. Ob-La-Di, Ob-La-Da
    2. When the Saints Go Marching In
    3. Happy Birthday To You
    4. Twinkle Twinkle Little Star
    5. Greensleeves
    6. J'ai Perdu Le Do
    7. Picnic
    8. Little Brown Jug
    9. The Nutcracker Suite
    10. Air On the G String
    11. The Skaters Waltz
    12. Autumn Leaves
    13. Silent Night
    14. Jingle Bells
    15. Last Christmas
    A fullsize version of MA-220 was Casio CT-400. Later keyboards of this hardware family had a changed sound set and no ROM-Pack support. These were with 49 fullsize keys Casio CTK-150 (30 songs, case like CTK-200), CTK-200 (40 songs), CTK-300 (40 songs, drumpads, chord sequencer, 2 speakers), KT-40 (crippled CTK-300, lacks SongBank & chord memory (likely addable as easteregg), has additional built-in cassette recorder and microphone jack with echo effect) and with 61 keys the CTK-450 (32 songs, 61 keys, only 64 sounds & rhythms, 2 speakers | all seen on eBay). The rhythm set varies among later models. A 32 midsize keys keyboard with "Do Re Mi Guide" and ROM-Pack was Casio PT-680. (Likely it more related to PT-88 than CT-840 hardware.)
     
     removal of these screws voids warranty...    
    WarrantyVoid
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