(noble My Music Center variant with 49 keys, accompaniment & many Asian/ Oriental demos)  Hmm...  ;-) Is this an essential equipment item on board of every JU-52 aeroplane and zeppelin?!?

Despite this midsize keyboard has a noble silver case design in a wonderful retro style, it unfortunately is one of the worst tablehooters, because (at least in unmodified state) nasty design flaws prevent reliable polyphonic play. Also many of the product features claimed on its German box and manual are (fraudulently?) false.

On the control panel stands "SANKAI-01870K" and "Elektronisches Keyboard mit 49 Tasten" ("electronic keyboard with 49 keys"). According to photos in the German manual, this instrument was also released as Miles MLS-490B. The Miles brand seems to be identical with Yongmei, the manufacturer of the likely worst keyboards of the world (see here). Very annoying is that in unmodified state only monophonic play is reliable possible because many key combinations don't work because the manufacturer omitted the key matrix diodes to save a few cents.

Generally there are many other things severely wrong with this tablehooter. There are not only a few Engrish misspellings on it, but the instrument has way less features like claimed on its German language box. Most blatant is that there are only 8 instead of the claimed 10 preset rhythms, and also other claimed features exist not at all, or only deeply buried inside the CPU as keyboard matrix eastereggs. The box claims:
 

original German box text:	translated into English:	comment:
49 Standard Tasten	49 standard keys	Keys are not "standard" (= fullsize) but midsize.
12Timbres/ 10 Rhythmus/ 8 Percussion instrumente	12timbres/ 10 rhythms/ 8 percussion instruments	Only 8 rhythm and 4 percussion instruments (on drumpads) exist on the instrument. (But 10 rhythms and 8 drumpads are supported by the CPU as key matrix eastereggs.)
Bass Akkorde automatisch/ per Einzelauswahl oder durch Mehrfingertechnik	bass chords automatic/ by single finger or fingered chord technique	Fingered chord mode does not exist.
Akkord/ Tremolo/ Portamento/ Infix/ Bass Effect	chord/ tremolo/ portamento/ infix/ bass effect	There are no such effect controls. Especially the portamento (glide tones) exists not at all (not even as part of the demos) on this instrument. It is also a mystery what "infix" shall be.
20 gespeicherte Demo Musikstücke	20 stored demo musics	only 16 are playable (4 are matrix eastereggs).
25 Level für Rhythmustempo/ 8 Level für Lautstärke einstellbar	25 levels for rhythm tempo, 8 level for volume adjustable	Volume control has 16, rhythm tempo 22 steps instead.

I am not sure if these false claims were made to fraud customers, or if the feature list on the box was simply copied from a predecessor or prototype version which indeed matched these specifications. Strange is that the B/W instrument photos in the manual have a "Miles" logo that was covered (by hand?) with "Sankai" and "01870K" stickers. Like with the infamous Yongmei tablehooters (see here), the AC adapter jack is wired parallel(!) to the battery compartment, thus any attempts to use it with batteries inserted may cause the batteries to EXPLODE (and also the microphone would certainly not survive to be accidentally plugged in here instead of the identical "MIC" jack next to it). Therefore this Chinese thing contradicts the "CE" rules and thus would be theoretically illegal to import into the EU (and certainly USA too). The German importer of this questionable plastic bomb is indicated on the box as:
 

Hergestellt für [manufactured for] Haltermann & Schulte Altenfelder Weg 13-15, D-27330 Asendorf/ Germany

Fortunately at least with some (fairly time consuming) modifications this tablehooter can be converted into a reliable working instrument. Very unusual is that the back of the manual shows a tiny (badly readable) copy of the schematics, which shows a different (and flawless!) template implementation of this hardware, which has a stereo amplifier and shows a key matrix with diodes and all (but one) keyboard matrix eastereggs.

main features:

• 49 midsize keys (a bit wacky and differently responsive)
• 2 built-in 10cm speakers (mono, sound very harsh & bassless, rumbling case distorts badly)
• polyphony 4 notes (only monophonic play reliable possible by missing matrix diodes | 2 notes with rhythm, only 1 note with accompaniment)
• 12 OBS preset sounds {banjo, harp, violin, bell, piano, organ, flute, trumpet, guitar, music box, saxophone, string}
• 8 OBS preset rhythms {rock, s.rock, disco, march, waltz, 8 beat, rumba, 16 beat}
• volume +/- buttons (16 steps)
• accompaniment volume +/- buttons (with rhythm (not drumpads), 8 steps, reduce DAC resolution badly)
• vibrato & sustain button (mislabelled "vib", "suatain")
• tempo +/- buttons (22 steps)
• fill-in button
• single finger accompaniment (only with rhythm, no manual organ chord mode)
• 4 plastic drumpad buttons {tom, low cowbell, snare, open cymbal} (icons instead show {snare, base, close cymbal, open cymbal})
• programmable 16 step rhythm pattern (custom drummer, very restricted)
• useless sequencer (monophonic record/ play of 21 notes, no edit, pattern is erased when anything else is pressed)
• same sound generator like in My Music Center (see there), but stereo with 8 sound channels (4 note polyphony) and less aliasing noise.
• CPU "M-35" (36 pin COB, crystal clocked  with 14.31818 MHz).
• battery alarm jingle
• 16 demo melodies (complex arranged including Asian/ Oriental ones, selected through 4 buttons)
• "guide" button to play the demos of bank 1 note by note.
• jacks for AC- adapter & microphone

Here are my new controls. Also the golden speaker rims were painted by me. German manual Hidden under stickers, the brand name "Miles" and model name "MLS-490B" appears.

eastereggs:

• 2 additional OBS preset rhythms {swing, rock 2} and 4 drumpads {base, close cymbal, high cowbell, handclap} addable.
• button for 3rd demo bank (oriental/ jazz musics?) addable.
• CPU outputs stereo  sound (needs 2nd power amplifier)

modifications:

polarity protection diodes added.

sound output jacks with speaker mute switch added.

wrong speaker polarity corrected.

keyboard & drumpads upgraded with matrix diodes.

redundant demo "SEL" button rewired for 3rd demo bank.

buttons for 2 additional preset rhythms + 4 additional drumpads added.

drumpads rewired to match icons.

upgraded to stereo: 2nd power amplifier with volume potentiometer added.

case de-rumbled by various measures.

notes:

Possibly the Sankai 01870K has one of the first Sankai CPUs, because although its 49 keys, crystal clocked hardware and accompaniment patterns already correspond to my other Sankai (sound bank) instruments, the preset sounds and OBS controls are still much like My Music Center. Like the latter, all preset sounds are made from each a static waveform and include a cold and glassy, detuned lo-fi chorus and some sustain (thus no very short notes can be played). But unlike the latter, the quite linear (unrealistic) volume envelopes have only little zipper noise, the aliasing noise of high notes is less extreme, and like with Feng Yuan 28061 the tremolo speed of the chorus varies much with the note pitch (the higher, the faster). All preset sounds start in a medium high octave range, thus no really low bass notes can be played despite 49 keys. The "piano" sounds rather honky- tonk- like; "guitar" is same but a bit harsher. Also the "harp" is similar but shorter, and "banjo" is even harsher and shorter (timbre is fairly realistic). The "bell" resembles a vibraphone, while "music box" is the same in duller (fairly realistic). The "organ" attempts to be a metal pipe organ rank. The "violin" is harsh and resembles more an accordion; "trumpet" is the same in duller and a bit more sonorous, "string" is even duller. Also "flute" is even duller and reminds to a human chorus. The "saxophone" otherwise is a very harsh harmonica timbre (about like the My Music Center "trumpet"). The "suatain" button prolongs the sustain phase instead of the release phase, and thus simply behaves like holding the key longer down for 0.5s instead of adding a real sustain. The vibrato ("VIB" button) is a highlight of this instrument; it sounds quite unique since it adds to the timbre a grainy (but not very strong) zipper noise texture that reminds rather a small dose of fast mandolin ring than a normal vibrato. Likely this effect modulates only one of the 2 suboscillators the chorus is made of, but unlike other My Music Center variants it does not disable the chorus, thus the tremolo of it is still present and only gets an additional texture (similar like the gritty 4 operator FM "ensemble" presets on Fujitone 6A or Yamaha PSS-390), which also makes the timbres a bit warmer and more harmonic.

The percussion of this instrument is made from low resolution samples, but sounds different and a bit better (less thin and noisy) than on My Music Center. The 8 OBS rhythms sound more generic than on the Sankai 01504H or K-Mark, since they employ no latin percussion but only base, snare and closed cymbal. All OBS rhythm preset buttons immediately (re-)start their rhythm, but also select a default tempo for each rhythm, which limits their use as a realtime sound control. The default tempo varies much among rhythms ("waltz" is very slow). The "fill-in" button always waits until the end of the current rhythm pattern before it inserts the fill-in pattern, and it also behaves a bit unpredictable, which limits its use a lot. With the "stop" button any rhythms or other sounds can be stopped immediately, which makes also a good realtime effect.

The single finger accompaniment knows only 3(?) chords. The accompaniment consists of e-bass and usually sweetish e-piano chords, and the styles are quite over- orchestrated and thus less versatile. Most styles contain a sweetish pop arpeggio and remind to Casio SK-1 accompaniments. By the limited choice of chords they can never sound nasty or disharmonic and also react a bit slow on chord changes. There is no manual chord mode (without rhythm). Strange is that the accompaniment section reaches to the 18. key of the keyboard (2nd octave "F") while the letters above the keys suggest it to end already on the first "B" (which would be more reasonable since there is no fingered chord mode). Confusing is that the "chord" button behaves like a synchro start feature and waits to the end of the current rhythm pattern before starting or stopping the accompaniment. Unlike the main volume control, the accompaniment volume control ("A.B.C. volume") very badly reduces the bit resolution of rhythms and accompaniment notes, which truncates their decay envelopes the earlier, the lower the volume is set. But this I consider rather a sound effect than a flaw.

Like the Letron MC-3 (see there) and many similar instruments, also the Sankai 01870K has a programmable (monophonic) drum pattern, but this one is very restricted because you can not enter pauses, nor it can be used together with accompaniments and not even the fill-in button works. You can only retrigger the user pattern with the "r.play" button, but stopping it by any means (the only way to enable normal rhythms and accompaniment again) always deletes the pattern. The user pattern is programmed by pressing "program" and then entering a sequence of drumpad button presses. Then press "r.play" to start. The pattern seems to be always 16 steps long. (The "r.play" button beeps with too few steps entered. With other such instruments the length depends on the previously selected rhythm; e.g. "waltz" would normally cause a 12 step pattern. The rhythm programming mode of the Sankai 01504H and K-Mark behave slightly more advanced because you can at least enter pauses.) Unlike preset rhythms, the user pattern and drumpads play always mono (centered position). Bizarre is also that the accompaniment volume control takes neither effect on the user pattern nor on manual drumpad play.

There is also a primitive record/ playback sequencer like with My Music Center, but this one is really useless since it stores only 21 notes and the pattern is deleted when anything else but "play" is pressed).
 

circuit bending details Like with the infamous Yongmei tablehooters (see here), the AC adapter jack of the Sankai 01870K is wired parallel(!) to the battery compartment, thus any attempts to use it with batteries inserted may cause the batteries to explode (and also the microphone would certainly not survive to be accidentally plugged in here instead of the identical "MIC" jack next to it). To fix this, solder each a diode into the +Vs lines from the battery compartment and from the AC- adapter jack to the electronics. CPU M-35 The "M-35" CPU of the Sankai 01870K has the same rectangular COB module package like in other Sankai keyboards. Very unusual for such a tablehooter is that the manual contains a picture of the schematics (although tiny and badly readable, like a fax copy), which shows the original CPU pin names. But it still took some time to figure out the pin assignment, because this CPU has its first pin at the top row of the right side (when the "M-35" label faces correctly) and from there the pins are numbered counter- clockwise (as usual). (no fullsize photo available) keyboard matrix control panel section cpu, stereo amplifier & reset logics To save space, I have only include the important parts here, since the piano key matrix is trivial and pins even mislabelled on these schematics.  This is the CPU pinout:   pin name comment 1 IOAB0 key matrix output 2 IOAB1 '' 3 IOAB2 '' 4 IOAB3 '' 5 IOAB4 '' 6 IOAB5 '' 7 IOAB6 '' 8 IOAB7 '' 9 IOCD0 '' 10 IOCD1 '' 11 IOCD2 NC 12 IOCD4 key matrix output 13 IOCD5 '' 14 VDD NC 15 IOCD6 key matrix output 16 IOCD7 NC 17 IOGH0 NC 18 IOEF7 key matrix input 19 IOEF6 '' 20 IOEF5 '' 21 IOEF4 '' 22 IOEF3 '' 23 IOEF2 '' 24 IOEF1 '' 25 IOEF0 '' 26 RESET reset 27 OSC1 clock crystal input 28 TEST crashes when touched 29 OSC0 clock crystal input  30 SLP NC (standby control output?) 31   +5V supply voltage 32 VSS GND 33 AVSS GND (audio ground?) 34 AUD1 audio out (left?) 35   '' 36 AUD2 audio out (right?) Most of the unused pins ("NC") seem to do nothing. Interesting is that there are 2 sound output pins {AUD1, AUD2} because the sound is genuinely stereo, although in the Sankai 01870K both outputs are connected with a mono amplifier. Warning: Be very careful with the "TEST" pin; connecting it with any output can permanently crash the CPU, i.e. the instrument won't start anymore even after power off and batteries removed. Only a manual reset (+5V through 1 kOhm on reset pin?) will re-enable the CPU. Although the "TEST" pin might be usable for shitshot, I am not sure if it only harmlessly messes up some static RAM contents, or if the "M-35" CPU is genuinely a modern programmed micro- controller, which "TEST" pin is a camouflaged PROM (or flash ROM) programming input that may permanently overwrite the ROM contents and thus destroy the CPU when fed with wrong signal patterns. keyboard matrix The key matrix has 15 output and 8 input lines. Very annoying is that the manufacturer omitted the key matrix diodes, which prevents reliable polyphonic playability. To fix this, solder a diode into the line of each key (49 in total). 1 2 3 4 5 6 7 8 9 10 12 13 15   pin AB0 AB1 AB2 AB3 AB4 AB5 AB6 AB7 CD0 CD1 CD4 CD5 CD6 in/ out   o o o o o o  o O. aSound  O. aSound  R. rock P. tom vibrato stop EF0 25 o o o o o o  D. bank 3 O. aSound  O. aSound  R. s.rock P. low cowbell sustain O. next EF1 24 o o o o o o   O. aSound R. disco  R. rock 2 P. high cowbell chord D. switch EF2 23 o o o o o o   O. aSound  R. march  R. swing P. clap D. guide D. sel EF3 22 o o  o o o o   O. aSound R. waltz P. base tempo +  record D. all EF4 21 o o o o  o o   O. aSound R. 8 beat P. snare tempo - R. program R. vol + EF5 20 o o o o o o O. aSound O. aSound  R. rumba P. closed cymbal volume + play R. vol - EF6 19 o o o o o o O. aSound O. aSound R. 16 beat P. open cymbal volume - R. fill-in D. melody EF7 18 Various function names in this chart were chosen by me and partly differ from the schematics. The input lines are active- high, i.e. react on +5V. 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. = rhythm P. = drumpad D. = demo O. = orchestra (main voice sound) orange background  = easteregg (unconnected feature) As eastereggs there are 4 additional drumpads, 2 preset rhythms and a 3rd demo song bank. Also a "next" button that steps through all preset sounds can be added, but it would be of little use since all sounds have their OBS buttons. I re-wired the drumpad buttons to match their panel icons and soldered a diode in series to each of them. To access the 3rd demo bank, I re-wired the redundant "SEL" button, because bank 1 can be already accessed with the "switch" or the "all" button. Bizarre is that this 3rd bank is not even mentioned in the original schematics. To make space for the new buttons and volume potentiometer, I sawed off the unused PCB corners. stereo upgrade & volume knob Although the CPU produces stereo sound, the power amplifier of this instrument is mono (an "LM386" IC) and thus mixes both sound channels together through each a 100 Ohm resistor, those common output goes through a single 100nF capacitor into the amplifier. To add stereo, desolder the upper end of the left resistors (where it is connected with the 2nd resistor and the 100nF capacitor of the amp) and also disconnect the sound output cable of the left speaker. Then connect the open end of the left resistor through another 100nF cap with an additional small power amplifier and connect its speaker output with the left speaker. I recommend for this to build the 2nd amplifier like the given one (using an LM386 IC and the below schematics) and connect its +Vs and GND lines with the ones of the original amplifier IC. This desoldered main PCB resistor outputs the left sound channel. Right next to it is the output resistor for the right channel. Regard that at least with my specimen one speaker had confused polarity, which prevents proper bass response. (The "-" pin of each speaker must be connected with GND.) If you want to add a real volume control knob, solder a potentiometer (100 kOhm is a good value) between the 100 Ohm resistors and the amplifier input. (Desolder the upper (initially interconnected) ends of the 100 Ohm resistors and solder them to the right pin of the potentiometer; connect the left pot pin with GND and the wiper with the 100nF capacitor of the amplifier input.) With the stereo upgrade use a stereo potentiometer (each one channel between 100 Ohm resistor and amplifier input). case de-rumbling With my specimen the sound of the internal speakers distorted badly because the plastic buttons, keys and PCBs rumbled badly at certain frequencies. To de-rumble the buttons, insert a foil of 1mm PE (polyethylene) foam or foam rubber between buttons and panel PCB. To de-rumble the key PCB, glue thin foam rubber on the left- and rightmost post that supports the key PCB. (Avoid too thick materials because they make the keys respond badly.) Other loose parts (speaker frames etc.) can be fixed with hotglue.

The demo musics of the Sankai 01870K are nicely arranged and vary a lot. Very unusual is that there are 4 different demo buttons and 2 demo song banks. Of the 1st bank (English & Chinese demos) the button "ALL" plays all of them in a loop, while "SEL" selects them in a sequence (one melody per press), and "switch" selects the same melodies through the white keyboard keys. The 2nd bank (Indonesian & Indian demos) is accessed in a sequence (one melody per press) by the "melody" button. Hidden in the CPU is even a 3rd song bank, that can be only accessed through a keyboard matrix easteregg (I rewired my "SEL" button for this). The demos are:

demo bank 1: (English & Chinese)

1. We wish you a Merry Christmas
2. Mary had a little lamb
3. Oh Christmas Tree
4. Good Morning [= "Little Bee"/ "Hänschen Klein"]
5. Little Brown jug
6. Happy Birthday
7. Fly. Fly. Fly. The Butterfly
8. Cradle Song [Brahms Lullaby]
9. Cloudy Moon [calm Chinese tune]
10. Whipping Horse moving food [fast Chinese melody]
11. Family Reunion [nice melancholic Chinese tune, resembles Japanese videogame highscore music]

1. [calm oriental tune, a bit like western movie?]
2. [calm western- style music]
3. [oriental blues music?]
4. [oriental tune, a bit western- style?]
5. [oriental blues music?]

1. [bluesy western- style music]
2. [disharmonic fast oriental tune]
3. [disharmonic repetitive Chinese blues?]
4. [bluesy "demo muzak"]

The Sankai 01870K hardware was likely also employed in the Keytone AB-490B (without omitted buttons, case like Miles MLS-4900A, seen on eBay).
 

removal of these screws voids warranty...
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