Pan Toys MC-7,
Trend Line MC 3700,
Fujiyama KS-37		 squarewave keyboard with analogue rhythm & monophonic accompaniment

These quirky keyboards belong to a very odd squarewave hardware class that was likely a predecessor of the Hing Hon EK-001 (see variant Transtec 893) and possibly MC-3. At the one hand it features accompaniment, programmable analogue rhythm and even a simple sequencer, but at the other hand the sound is plain squarewave with the most crude and primitive volume envelopes you can imagine; the whole thing is only 2 note polyphonic and the automatic single finger accompaniment features neither chords nor a separate bass line but simply occupies the 2nd melody voice with a monophonic pattern.

But these instruments are nothing bad; they sound just in a sympathetical way artificial and puristic and have much similarity with music from historical videogames or simple Commodore C64 homecomputer compositions. Especially the accompaniments sound nicely cheesy and innocent. The key response feels very direct, so like on a 1970th transistor organ you can play extremely short blip notes without getting into trouble with slow matrix scanning or too "intelligent" software that tries hard to prevent irregular sounding notes.

(Note: This thing sounds quite nice, but don't buy one of these so far your only intention is to get a keyboard with faithfully imitated natural instrument timbres. Remember, this is a squarewave instrument and its sounds do not even remotely resemble what is written on its buttons, thus bought with wrong expectation it may disappoint you.)

Pan Toys MC-7

While the front panel of this instrument is labelled "MC-7", on the back of the case stands also the brand name "Pan Toys".

This instrument was also released as Elite MC-7, GPM MC-7 and Levis MC-7 (seen on eBay).

main features:

(old eBay picture of my specimen.)
PAN TOYS MC-7

eastereggs:

This is one of the keyboards I believe to have seen as the smallest "Fujitone" in shopping centers of my childhood; particularly I remember well how I mused about its lousy "xylophone" sound and the colourless drums at a time where the first Casio ToneBank keyboards (SA-20 etc.) appeared with lots of (at that time) very realistic sounding timbres. The MC-7 has no sound output, even the lowest volume setting is quite loud and it generally sounds quite bright and a little harsh (analogue distortion?), but the timbre is still pleasant. (I didn't modify this tablehooter because I also own the TrendLine MC 3700.)

The sounds are extremely odd, because the timbres are just plain squarewave with different pulse widths and so archaic, crude volume envelopes that even a Letron or Casio VL-1 sounds almost natural against it. When sustain is switched off, after releasing the key any sounds stop immediately with an audible end click, and the sound presets itself also contain neither vibrato nor tremolo. The squarewave timbres are quite bright and some have a grainy purring texture; it is not zipper noise but sounds like an intermodulation with internal digital signals. When 2 notes are held, the timbre flutters with a strange irregular textures, which sounds quite interesting. Similar like the simple MC-11, this instrument permits (with some skill) to play extremely short, blipping notes those most modern keyboards ignore or render too long. The 'clarinet', 'violin', 'oboe' and even the 'elec. guitar' are nothing but plain squarewave tones of different pulse widths without any envelope (i.e. a simple toot or beep like from a cash register or similar). The 'piano' and 'harpsichord' have a decay envelope, but with sustain enabled they ignore the key press duration. The 'xylophone' is nothing else but a short beep (1/8s?, has same decay envelope that stays inaudible) with sudden end click, which stops without sustain even earlier by releasing the key, but also with sustain it won't get longer than its maximum length (which is much shorter than e.g. the 'piano' or any of the continuous tone sustains). The 'mandolin' of this little tablehooter even rings (about 8Hz), but like the latter it can also not be really prolonged by sustain. An oscilloscope reveals, that the 'violin' and 'e-guitar' have a purring texture made by the envelope trigger signal (seen in Fujiyama KS-37) that contains a texture looking like inverted 'mandolin' ring signal (i.e. steady level with short drops at 8Hz), which was likely intended as a tremolo, but the volume modulation stays almost inaudible by the fully charged envelope capacitor. The sustain duration with other preset sounds corresponds to the held 'piano' envelope. The vibrato button adds a 6Hz tremolo instead of a real vibrato.

Unlike the Letron and various similar squarewave keyboards, when OBS sound preset buttons are pressed with held down keys, this instrument does not immediately switch the timbre of the still sounding notes, but assigns the new selected sound either only to the next played notes or makes the held notes fade silent and then retriggers them with the new timbre. What exactly happens depends on the previous and new selected sound preset; e.g. a held "mandolin" note stops ringing as soon a different sound is selected. This can be used as a sound effect, although the behaviour can be difficult to predict.

Like the arpeggio of other instruments, the accompaniment can play in different keys despite it is monophonic; for this simply 1 or more keys in the left keyboard section have to be pressed, similar like a single finger chord (1 key= minor, 2 keys= major, 3 keys= 7th or the like). Although the accompaniment plays always the waveform of the currently selected main voice sound (including the vibrato setting), it turns it into an organ without decay envelope and uses no sustain; even the mandolin ring is strongly reduced.

Rhythms can be switched immediately and always (re-)start from their 1st step as soon any OBS rhythm button is pressed. With some skill this can be uses as a realtime variation feature. The rhythm only employs 2 dull analogue drums (like muffled congas with short decay envelope) and a hihat. With my first MC-7 the hihat sounded quiet like hit with too little force. Later I bought another Pan Toys MC-7 (to gut out for repairing my rare Fujiyama KS-37), which hihat sounded noticeably louder with more percussive attack (like a brushed snare); possibly one had a broken electrolytic cap or different discrete components.

The monophonic sequencer is useless because it holds only 28 notes and does not work with rhythm (turns it off during record or playback). The "custom drummer" otherwise can be combined with the preset rhythm accompaniments, and even length of the drum pattern depends on the selected preset rhythm, thus it is a quite interesting feature that may be good for tekkno. (The analogue drums can be likely circuit-bent similarly like I did with my HBATEC.) Unfortunately the drumpads are monophonic and so can not play multiple percussion simultaneously.
 

hardware details

The Pan Toys MC-7 is based on the single-chip CPU "SC-MC-2", which outputs 2 squarewave sound channels and trigger pulses for envelope and analogue percussion. The CPU analysis is also valid for other MC-2 based instruments.

The PCB is rather small, and like the bizarre HBATEC it contains only one digital IC and lots of analogue stuff (mainly percussion).
There are also many unused drill holes without traces on it. Likely this was intended for the sustain envelope shortener found in other MC-2 based keyboards.

The analogue envelopes are very primitive; they can only decay or stay absent. The envelope trigger pins 3, 4 control each a transistor circuit of a simple VCA and capacitors. There is no slow attack, thus the tone always starts immediately (with a soft key click) after key press. Without enabled sustain, the CPU stops the tone immediately after key release. With sustain on, in TrendLine MC 3700 and Fujiyama KS-37 the decay rate in some preset sounds is faster (by pulling CPU pins 18, 19 lo - not used in MC-7 and Medeli MC-2000A). Unfortunately even with sustain on, the CPU switches the tone generator off after 1s, thus no modification (except clocking the entire CPU and thus pitch lower) can make longer than 1s decay time. (It may be that in a prototype the VCA failed to completely mute a channel after decay and so this annoying decision was taken to prevent it from tooting in the background.) And (how stupid is that?!) the programmer missed the chance of using pin 18 or 19 for also shortening the 'piano' and 'harpsichord' sustain after key release; so they still ignore key press duration. (May be this was even the original intention of having 2 identically behaving pins for each a polyphony channel, but the programmer ran out of memory or time.) Continuous tones hold their envelope trigger pin active (lo) so long the key is pressed. Decaying tones only start with a short spike to charge the capacitor. The 'mandolin' envelope repeats this with 8Hz to make it ring. The 'mandolin' and 'xylophone' decays with the same rate like others, but stops the tone (not envelope) already after about 1/8s; that's why it sounds rather like a short beep, because the (barely percussive) envelope has no time to decay sufficiently. The envelope trigger signal of  'violin' and 'elec. guitar' is the inverted version of 'mandolin', i.e. it it has short gaps with 8Hz to make the level sink a little for a fast tremolo, which however is nearly inaudible because the fixed decay rate is way to slow to do much. So likely originally a faster decay was planned but not implemented. Such things are the strange little secrets of squarewave tablehooters those make it worth to analyze them, because they do differ from the theory of classic analogue synths in ways you don't expect.

When the RC timing constant is shortened by modification (done here in Fujiyama KS-37), the xylophone sounds more credible and the inverted mandolin envelope adds a buzzy purr timbre to 'violin' and 'elec. guitar'. But because this also makes e.g. 'piano' decay faster, extreme values are of little use. (It might even be that instead of purr only a minor volume reduction through a kind of PWM  in some sounds was planned, but the presence of a rhythm volume control makes this unlikely.)
 
sound pulse width  hi octave long sustain envelope trigger
clarinet 1:1
 
 
 continuous
oboe 3.25:1
X
 
 continuous
violin 2.16:1
X
X
 inverted mandolin ring
xylophone 1:1
X
 
 spike, tone ends after 1/8s
piano 3.5:1
 
X
 spike, tone ends after 1s
mandolin 15:1
 
 
 mandolin ring (spikes 8Hz), tone ends after 1/8s
harpsichord 15:1
X
X
 spike, tone ends after 1s
elec. guitar 2.2:1
 
X
 inverted mandolin ring
Some preset sounds play an octave higher or have longer sustain, but the waveforms only differ in the pulse width ratio of the squarewave. (The ratios were estimated on an analogue oscilloscope, which isn't very accurate.)

The default after power-on is 'clarinet'. The accompaniment always uses the currently selected main voice without sustain.

With enabled vibrato, CPU pin 17 outputs a 6Hz LFO signal. Because the instrument is crystal clocked, the LFO simply modulates the transistor based VCA and thus produces rather a tremolo.

The preset rhythms don't trigger hi and lo conga simultaneously. Traktor told me that in his Medeli MC-2000A a simplified drum circuit with a single oscillator for both drums is used (empty solder holes for the 2nd still exist), which only switches pitch when the higher drum is played. Strange is that in "custom drummer" mode not even even hihat can sound together with drums, so I expect that (like seen in Casio VL-1 patent) it stores each percussion step as a 2 bit number to save RAM space, i.e. any step can be only {pause, lo conga, hi conga, hihat} and thus can not play multiple percussion simultaneously.

keyboard matrix

The matrix is based of my analysis of Fujiyama KS-37 (based on my too messy old handwritten documentation of TrendLine MC 3700).
 
30
31
32
33
26
27
28
29
 
CPU pin
in 1
in 2
in 3
in 4
in 5
in 6
in 7
in 8
in / out
 
o
F1
o
F#1
o
G1
o
G#1
o
A1
o
A#1
o
B1
o
C2
out 1
38
o
C#2
o
D2
o
D#2
o
E2
o
F2
o
F#2
o
G2
o
G#2
out 2
39
o
A2
o
A#2
o
B2
o
C3
o
C#3
o
D3
o
D#3
o
E3
out 3
40
o
F3
o
F#3
o
G3
o
G#3
o
A3
o
A#3
o
B3
o
C4
out 4
41
o
C#4
o
D4
o
D#4
o
E4
o
F4
o
(F1)
o
(F#1)
o
(G1)
out 5
34
O.
clarinet
O.
oboe
O.
violin
O.
xylophone
O.
piano
O.
mandolin
O.
harpsichord
O.
elec. guitar
out 6
35
R.
waltz
R.
march
R.
rock
R.
bossanova
R.
pops
R.
disco
R.
rhumba
R.
16 beat
out 7
36
demo
S.
record
S.
play
R.
program
tempo
+
tempo
-
auto accomp
R.
stop
out 8
37
P.
lo conga
P.
snare
P.
hi conga
R.
play
vibrato
sustain
R.
start
R.
synchro
out 9
20

The input lines are active-low, i.e. react on GND. Any functions can be triggered by a non- locking switch in series to a diode from one "in" to one "out" pin. Very unusual is that the keyboard matrix inputs of this CPU respond only on rather low resistance voltages (about 330 Ohm).
 

legend:
"o"
 = keyboard key
R.
 = rhythm
O.
 = preset sound ('orchestra')
P.
 = drumpad
S.
 = sequencer
orange
background 		 = easteregg (unconnected feature)

There are 3 additional low bass note keys addable at pins 27->34, 28->34 and 29->34. Unlike normal low note keys, these don't affect accompaniment and have (depending on selected preset sound) a changed pulse width (in some sounds 28->34 differs again), so they may be a bug or test feature.

The drumpads behave a bit odd. They are only monophonic (despite preset rhythms can play hihat simultaneous with a drum). When a 2nd pad is held, it will sound only after the 1st pad is released.

pinout SC-MC-2

The "SC-MC-2" (42 pin DIL) by Medeli is the CPU of the MC-2 series keyboard hardware class. It has internal ROM and outputs 2 squarewave sound channels and trigger pulses for crude capacitor envelope and for 3 analogue percussion. This is one of the most basic home keyboard CPUs with accompaniment, because instead of chords it only uses the 2nd melody voice channel for a kind of arpeggio.

It is likely the same OKI microcontroller like MC-3DX (which uses an external sound IC) of the famous MC-3 keyboards with changed software to produce tones by itself. Historically important is the lower number, which hints that this was either a predecessor or cheaper variant made by Medeli.

This pinout is based on my analysis of Fujiyama KS-37, my old handwritten description of TrendLine MC 3700, PCB photos of MC-7 and few guesses from MC-3DX. The pin names were taken from the "SC-MC-3" pinout in book "Keyboard Principles" (typos fixed by OKI MSM6404VS datasheet) and line names chosen by me to describe their functions (partly inspired by Casio naming conventions).
 
pin name line purpose
1 P4.0 M1 melody1 tone out
2 P4.1 M2 melody2 (accomp) tone out
3 P4.2 /ME1 melody1 envelope trigger out
4 P4.3 /ME2 melody2 envelope trigger out
5 P3.0 /RH1 lo conga trigger out
6 P3.1 /RH2 hihat trigger out
7 P3.2 /RH3 hi conga trigger out
8 P3.3 AE accomp envelope out (in Fujiyama KS-37: wired to GND)
9 OSC0   crystal in (4.0 MHz)
10 OSC1   crystal out
11 /RESET   reset
12 TEST   clock out (0.89 MHz?, not used)
13 P2.0 /INT   (hi)
14 P2.1   (hi)
15 P2.2   (hi)
16 P2.3   (wired to ground 0V)
17 P0.0 VIB vibrato pulse out (off=lo)
18 P0.1 /SCK MEL1 sustain length out (used in Trend Line MC3700, Fujiyama KS-37)
19 P0.2 SO MEL2 like 18 (used in Trend Line MC3700)
20 P0.3 SI KO9 key matrix out
21 GND   ground 0V
pin name line purpose
22 /CIN P1.0 /L1 accomp led out (not used)
23 /TMO P1.1 /L2 tempo led out
24 /TCK P1.2 /L3 record led out
25 P1.3 /L4 program led out
26 P8.0 KI5 key matrix in
27 P8.1 KI6 key matrix in
28 P8.2 KI7 key matrix in
29 P8.3 KI8 key matrix in
30 P7.0 KI1 key matrix in
31 P7.1 KI2 key matrix in
32 P7.2 KI3 key matrix in
33 P7.3 KI4 key matrix in
34 P6.0 KO5 key matrix out
35 P6.1 KO6 key matrix out
36 P6.2 KO7 key matrix out
37 P6.3 KO8 key matrix out
38 P5.0 KO1 key matrix out
39 P5.1 KO2 key matrix out
40 P5.2 KO3 key matrix out
41 P5.3 KO4 key matrix out
42 VDD   supply voltage (+5.5V)

CPU pin 18 and 19 both are hi during the preset sounds {violin, harpsichord, e-guitar, piano}. Strange is that in my Fujiyama KS-37 their hi level is only +2.5V, which likely was result of CPU overvoltage damage, because in MC-7 (which does not use them) it is regular +5V. In the KS-37 only pin 18 goes to a transistor circuit that apparently connects an additional 1uF capacitor to the envelope section. In Trend Line MC3700 both pins are used, which may be the reason why 2 simultaneous notes here do not cause long sustain. Preset sounds {violin, e-guitar} show the inverted mandolin ring pattern on their envelope pins, which was likely intended as tremolo or to lower the output volume. During vibrato pin 17 outputs a squarewave LFO signal. Pin 8 is hi during each accompaniment note that is played or would be played (i.e. when rhythm is running, also when accomp=off); likely this was designed as an envelope trigger, but not used because it stays on when accomp=off (may be masked out using the signal from pin 22). The unused pins 13..15 stay hi with high resistance, thus they are likely unused inputs.

When the CPU locks up by empty batteries, it mutes both polyphony channels and controls do not respond anymore, but the selected rhythm keeps running. This hints that its hardware (or IRQ routine without RAM?) can loop a bit pattern on an output port by itself even when the rest (RAM contents?) has crashed.

Close successors of this CPU were the SC-MC-21/SC-MC-22, those implement additional 3 note polyphonic accompaniment and better envelope control.

Unlike the (Zilog based) "KZ" CPUs of Angeltone hardware (like HBATEC, Fujitone 3-A), the entire Medeli "MC-SC" CPU series has percussion trigger and LED outs not embedded into their keyboard matrix but on separate pins, which strongly hints that they were designed by different programmers. MC-SC also seem more precisely tailored for the instruments they are used in, and so have fewer interesting eastereggs.

Besides that it is much bigger (midsize keys), the MC-7 case design resembles very much Hing Hon EK-001, and indeed also a mini keys version of it was released as Elite MC 2000, Transtec 893 and Grand Prix KB 893, which case looks besides the different button layout exactly like my EK-001. A case variant of the MC 2000 with centered drumpads shaped like Casio SK-5 and SK-8 was released as Fujitone II and Monacor MC-2000A (see below).

Trend Line MC 3700

This instrument is based on the same CPU like Pan Toys MC-7, but has a different PCB with somewhat better envelopes. It sounds less harsh (e.g. the clarinet sounds more credible; likely by different capacitor values). Also the drums sound different; they are more melodic here and particularly the high tom resembles more a muffled plastic pot and does not resemble at all a base drum like the MC-7 one.

Very unusual is that this instrument has no master volume control, but only 2 separate "faders" for main voice and rhythm volumes, those behave totally independent (i.e. reducing the "main volume" does not also reduce the rhythm volume).

Due to strong similarities, I only discuss here the differences to Pan Toys MC-7.

different main features:


(old eBay photo of my specimen)
My specimen is severely yellowed (keys almost brown). I am not sure if this was only sunburn by the previous owner or if the plastic decomposes somehow by wrong chemistry. The surface under removed key stickers look less yellow, so it likely indeed just ate way too much sunlight. Above the power supply jack are remains of a strange sticker, warning to switch power off before connecting the AC-adapter. I never saw such a warning before; possibly it may crash and not reset properly, but since there is no internal battery backed up memory to corrupt, all other risks (e.g. intermediate short between internal batteries and power supply inside the jack) are the same when on or off. (Traktor told me that his Medeli MC-2000A has that sticker too.) This hardware uses both envelope control pins to shorten sustain in certain sounds, which is most noticeable with 'oboe', where short notes resemble a picked string.

This instrument was also sold as Bestar MC 3700, Mundia MC-3700 MP180, XJ 37 F 370 and Kamosonic F1. The case design of this instruments has many style elements common with the MC-3 keyboard Tristar MC 3000 and the GPM MC-5000.
 
 
Fujiyama KS-37

This was my first specimen that I found of the MC-2 hardware class. It was sold to me on flea market and seems to be ultra-rare, but unfortunately mine was completely brain-dead; apparently someone before me confused the AC-adapter polarity and though toasted it, or the dead zener diode killed it by overvoltage. The only still working parts were the amp and the transistorized analogue drum circuit. Later I repaired it with parts from a Pan Toys MC-7.

The case is brown and the speakers are left and right next to the keyboard instead of above it ( =>wastes space). It has 3 orange drum pad buttons and most other controls are similarly labelled like the Letron, but the keys are slightly longer than normal midsize keys. The instrument has a nicely warm timbre and slightly better envelope hardware than MC-7. Annoying is that volume can not be set lower than medium ambient volume. Due to strong similarities, I only discuss here the differences to Pan Toys MC-7.

This instrument was also released as Tokyo KS-37 (seen on eBay).

different main features:

The slightly slanted side speakers are a well recognizable style element of this case; I believe to remember that old Fujitone keyboards featured them also. The drumpads have wrong icons {base, snare, open hihat}; genuinely they play {lo conga, hi conga, closed hihat}. Shape resembles Hing Hon EK-001.

eastereggs:

modifications:

notes:

The "power" LED is labelled "tempo" despite it does not flash; instead the LED above the "accomp" button does this job (despite the CPU has an unused pin to show its button state), so it is likely a PCB layout bug. The decay envelope of my specimen was quite long, so it blurred the mandolin ring and turned 'xylophone' into a short toot; I thus installed a trimmer to shorten it. But unlike Trend Line MC 3700, in preset sounds with short sustain 2 simultaneous notes add here long sustain, which may be result of simplified envelope processing (KS-37 has fewer electrolytic capacitors) that uses only one CPU pin.

The Fujiyama KS-37 looks quite much like what I remember from my childhood as a "Fujitone". I would love to find one of these first Fujitones (not a Fujitone IIIb but a really old one). A variant of the Fujiyama KS-37 with similar case but more rectangular speakers and drumpads was apparently released in China with the brand name Tongmei (not Yongmei, seen on eBay).
 

hardware details

Also the Fujiyama KS-37 is based on the single-chip CPU "SC-MC-2".
Mine was brain-dead, so I later repaired it with parts from a 2nd Pan Toys MC-7 that I bought for this on eBay. I soldered in a socket for the new CPU (40 pin socket + piece from another socket to get 42 pins), and at low voltage it indeed seemed to work, although there was plenty of mains hum from my unregulated AC- adapter. But when I increased the voltage (jack was labelled 9V), the CPU crashed and didn't start anymore for many minutes. I first thought I had toasted it - arrrg! - But after waiting about 30 minutes, at low voltage the instrument worked again. I examined the PCB and found out that the zener diode that together with a transistor was intended to regulate the CPU voltage was defective (open, took no effect) and thus the CPU got almost the full supply voltage instead of only 5V. Either the original CPU died by that faulty zener diode, or the confused polarity by the previous owner not only toasted the CPU but also the zener diode. I replaced it with the zener from that MC-7 to protect the CPU properly. 

noise reduction

After repair it worked well now but there was still much mains hum because the GND line was wired very badly; the entire ground current of the supply voltage was drawn through the audio GND line at the volume potentiometers and thus caused a voltage drop. I separated both grounds and wired the audio and audio GND lines separately with a shielded cable to the amp section =>hum is gone. Initially also the left speaker had wrong polarity, but wiring it correctly didn't boost the bass response really much.
 
I first hoped this rare instrument had different analogue percussion (and made use of the mysterious 4th drum output of the CPU), but it doesn't differ that much from MC-7.  The 2 drums are quite dull with short envelope; the higher one (bongo or high tom) sounds like a muffled plop noise that reminds to opening a plastic bottle. At higher volume setting the drums distort and thus get more percussive. Despite like with other MC-2 variants the power LED is mislabelled "tempo" and has a separate lead to the main PCB, here it doesn't flash but the unlabelled LED above the "accomp" button flashes instead. Bizarre is also that on the button names are printed on the back of the control panel PCB, but many of them differ from the actual control panel writing and they have plenty of Engrish misspellings.

envelope decay control

The envelope decay control from CPU pin 18 goes to transistor Q6, which connects the electrolytic cap C9 (1uF) with the VCA transistor Q8 to make sustain decay slower if pin 18=hi.

In my KS-37 the envelope decay was too slow, which e.g. blurred the mandolin ring pulses. The resistor R21 controls the decay rate of the envelope circuit. Reducing it makes it decay faster, so I wired [a 100k trimmer in series with a 10k (safety) resistor] parallel with R21. With my specimen a total value of 25K sounds like the best compromise for 'xylophone' and mandolin'. But this method is not perfect; during 2 simultaneous notes the sustain still sounds too long (by charging a capacitor too much?).

You may install a potentiometer with the right end of the carbon trace cut to keep the original value when turned rightmost. Regard that you can not make decay time longer than it is, because the CPU switches the waveform off after 1s (1/8s in 'xylophone' and 'mandolin'), so slower decay only emphasizes the end click because volume falls less before the tone stops.

other MC-2 variants

These are some pictures and model names I found on eBay:
Transtec 893

same case:
Elite MC 2000
Gran Prix KB 893
Rhapsody

This was the direct predecessor of
Hing Hon EK-001.
Fujitone 2 (Fujitone II)

same case:
Antonelli ART-2450 (bluish)
Medeli MC-2000A
Monacor MC-2000A
Kazama EK-828 CP

Tongmei
Instruments of this hardware class can be recognized by the combined power & tempo LED (i.e. the power LED is labelled "tempo"), the presence of 8 OBS rhythms and 8 OBS sounds, 3 drumpads with 2 custom drummer buttons and the sequencer "record" and "play/ stop" buttons. Regarding the CPU type label, also a variant called "MC-2" may exist, which appears to be the genuine name of this hardware class (e.g. MC-3 keyboards (like Letron MC-3) also have "MC-3" in their CPU name). A possible direct predecessor of the MC-2 hardware class was the Superb Sound EK-922. A possible successor was the Elite MC2200. Another keyboard with similarly cheesy monophonic accompaniment and analogue rhythm is the nice Casio MT-40.
 
 removal of these screws voids warranty...    
WarrantyVoid
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