keyboard – Trevor's Repair Café

Excel-O-Tone

2 euros at the thriftstore, don’t mind if I do! The Excel-O-Tone is pretty much a dumbed down Casio VL-1. It makes monophonic bleep bloop noises with a parrot button that repeats your last played x amount of notes. You can add in vibrato on the bleep bloops and that’s about it. Also I haven’t got a clue what a Yoko is besides an exquisite musician and artist from Japan.

Features

Power on/off switch
25 keys
1 oscillator (monophonic)
4 volume levels
4 tempo levels
Off-On-Off vibrato function
Note sequence repeat button
No clue what the “auto” button does, it just stops all keys from making sound
Headphone output (3.5mm)
Battery powered (4x AA @ 1.5V)
2 extra spots to store batteries for your calculator or something?
DC IN (probably 6v)
Yellowed

Why it sucks

Wonky key response. Keys don’t register when playing too fast, sometimes stutter, sometimes plays an x amount of time even after letting go. Not very musician friendly so to speak.
Vibrato not very convincing, also why is that switch off-on-off?
The sequence repeat function doesn’t take rhythm in account, every note plays for the same duration.

Teardown

First thing we see are two speakers (such a luxury!) a small PCB on the bottom for the DC IN and headphones out and a big PCB on the top which has all the rest.

Zooming in on the interesting part shows us what they use for clock, microcontroller and audio output amp.

My guess is the CD4069 (Hex inverter) has some function as clock for the COP420 (datecode week 8, 1985) that happens to be a 4 bit microcontroller which also handles all the other functionality like the “keyboard” and other switches and buttons.

They chose to use an LM386 (type 1) as driver for the two speakers. Why they use two speakers is a cost-cutting mystery to me as the “synth” is mono. To make matters worse, it seemed like the speakers were connected out of phase which initially gave me acoustic headaches while playing the bleeps and bloops. I decided to swap the wires of one of the speakers to fix that.

Always interesting to see the manually routed single sided boards. If you didn’t know yet, the PCB designs were laid out with tape! This is why the tracks look so wobbly. The keys just use a membrane type-o technology. Nice and cheap. The switches are stuck on the PCB by those black plastic frames. No way to replace them if something were to happen to them!

Note the unused footprint in the top-left corner. Seems like they were also in the process of copying the calculator which could be found on the Casio VL-1.

Bontempi 123765 Keyboard

Why do I even bother with toys you ask? Well it was cheap at the thriftstore and the keys felt very usable for other projects if the keyboard tuned out to be broken or straight up useless.

So I already featured some Bontempi on here, especially because they also made a ton of very beautiful vintage instruments but then went the cheapo children’s toy road and here we are.

The sounds are horrible, the features horrible, the thing is buggy and glitchy and indeed only children would enjoy it. It’s like a christmas card with knobs.

Features

On/Off toggle switch
3 sounds (pulse, piano(?), violin)
8 rhythms
24 songs with demo song button
Microphone input (wow!)
DC voltage input (+6VDC) or 4 AA batteries
37 keys (but there’s a catch!)
Volume control (2 stages: normal and overdrive)
Rhythm select and stop button (but there’s another catch!)
Sound effect button!
Tempo up and down buttons (more catches here…)

Why it sucks

The black keys do not work as expected. They just play the nearest white key to the right. In short, this keyboard is in C major but they even fricked that up by having the A key play a A#. Very fonky.
When you start a rhythm and want to play along, you will be disappointing. As soon as you play a note the rhythm ceases to exist.
Keyboard is monophonic but the demo songs polyphonic.
The louder volume setting quite literally overdrives the amplifier chip. Poor parents.
There are 2 tempo buttons for the rhythms but they both perform the same function: they toggle between two BPMs.
The sound effect button adds a pleasant tremolo to the pulse sound, but on the other two its for some reason 3x faster.
Keys cannot be held down, the sounds just stop playing after a second. Actually, the timing is dependable on the pitch of the note as higher notes are just the 1 second sample played faster.
Microphone input is very quiet, volume buttons have no effect on it. Obviously a poor passive mixer on the amplifier chip.

Teardown

So what makes this toy tick…

We turn the thing over and remove many many screws around the perimeter of the keyboard, and the back lifts off. Obviously, be careful as the battery terminal wires are connected to one of the PCBs.

Sooo… 1 speaker, a funny looking PCB in the top left, a loooong PCB for the keys and some flatcables going to a very specific PCB.

MQ386F-…, yeah yeah yeah, just the amplifier board. Utilizes our good friend the 386 in SMD package. Nothing else noteworthy here.

The other side, just some electrolytic and the +6VDC power and mic input. The most shocking feature of this PCB is the unused USB footprint. Did they ever plan to add USB to this? You would be surprised if I said that the enclosure actually also has an unused cutout for a USB. Would it be used for charging some lipo? to actually send midi data? to just power the thing with a phone charger? Will we ever know?

Ah the brains of the machine, SLAB-2. Yes, friends, this is just a black blob microcontroller which controls everything from button presses to sending out audio.

In closure

It is trash.

The PCB with the rubber and carbon thingies to register key presses is actually fully equipped to also register the black keys just fine, they just went cheap.

It would be fun to find out if the chip does anything with USB but as I have no clue what to connect with what, we will never know.

Portable Electronic Keyboard

Full album made with the sounds of this keyboard!

A two euro thriftstore find of some brandless keyboard that makes some funky noises. I can’t really put a date on it but it is probably some 90s equipment because the plastic housing is actually quite sturdy.

In the box is only the keyboard itself and a tiny paper which is supposed to function as manual, fully in German. Some genius left 4 AA batteries in there that started leaking but I won’t be using batteries anyway because this keyboard has a DC input jack for 4.5 to 6VDC. Great!

Functionality

Some specifications and stuff:

37 tiny keys, no velocity sensitivity here
4 non programmable drum pads
2 note polyphony, duophony?
8 “instruments”
8 “rhythms” (rhythmical rearrangement of the 4 drum pad sounds)
Rhythm start and stop knob
Rhythm timing LED indication
Tempo up and down control (16 levels of tempo)
Vibrato function (actually quite cool and non-intrusive)
Demo knob (Plays Greensleeves melody with whatever instrument selected)
Microphone input
Headphone output
4.5-6VDC input (center positive) or 4x AA batteries
Mono speaker to the left
Master volume stepped control
Microphone volume stepped control
On/off switch with power LED inducation

Tear it down!

It takes about 8 or so philips screws to get the back lid off. Have to be careful cause there are flimsy wires connecting the battery terminals to the keyboard… board.

So yeah, batteries on the bottom lid, speaker bolted to the left, a brown single side PCB for switches, buttons and jacks. Smaller green PCB for all the digital stuff and power amp for the speaker. Connections are made with flimsy wires and those vintage ribbon cables that barely move cause they have solid core wires inside.

Now, this board is soldered by children or something (wouldn’t be surprised), there is stray solder everywhere but I guess it passed quality control. The nice part of the PCB is that if you look carefully, there are indications of components and padnames on the PCB.

Like to the right, SP for speaker, VCC, a +6v rail and a +5v rail. And to the left some designators for the throughole components. The big star of the show, the digital chip (which has all the logic and sounds on it) is the only SMD part in the whole thing.

Due to the nature of the shitty ribbon cables it was hard to peak under the PCB where all the goodies are. To the right a giant black SMD IC I mentioned before. To the left an LM386 doing its power amplifier job. Interestingly also a trimmer potentiometer. I’m not quite sure what its job is but I assume global tuning of the instrument but I haven’t tried. The fun thing is, this whole instrument is terribly voltage controlled. Modulate the power supply and you will modulate the pitch. The circuitbending community goes wild!

A close up of the speaker side of the keyboard. 1W 8 ohms, nothing special here and on the brown PCB are some more passives doing who knows what.

I didn’t bother to get the brown PCB out, it will not be exciting at all. It will probably look very similar to the board of the Bontempi BT 805.

The incredible noise killing mod

When powered by a noisy source like a phone charger, the keyboard won’t like you. The speaker starts buzzing and just won’t shut up. Using a good PSU or a linear one fixes most of the problems. To fix it even more, I invest 2 cents by soldering a random 470µF capacitor to the +5v rail to ground. Problem solved!

Sounds!

Here is a collection of various sounds the keyboard can make, enjoy!

All 8 instruments, vibrato on, MUSIC BOX – VIOLIN – FLUTE – ORGAN – GUITAR – BANJO – HORN – PIANO

It’s noticeable how most of these “instruments” sound like retro 8 bit sounds, quite fun to play with. Violin tries the hardest to actually be a real instrument. Organ is a mystery to me what it is trying to sound like. Banjo is interesting cause it has an asynchronous tremolo going on. It is possible to trigger a note right when it is silent, which is quite annoying honestly. Piano is just a horn with a shorter decay.

“Horn”, without and with vibrato

All 8 rythms, DISCO – BALLAD – MARCH – SWING – POP – WALTZ – RHUMBA – TANGO

Rhythms at different tempos, can get quite fonky!

The 4 percussive sounds, feel free to sample, KICK – SNARE – HIHAT – “COWBELL”

The kick is just a decaying note, actually interferes a lot with bass heavy instruments like the “horn”. The cowbell is just a joke.

Greensleeves demo song featuring all instruments with no vibrato

The same but with vibrato

And to finish the article, a piece of music I created in 5 minutes by layering many of the instruments and trying to keep time with the drum pads, enjoy!

Standard SR-T115 Cassette Recorder

Another cheap thriftstore find. This 1968 cassette recorder comes with a (electret) microphone and runs on 6VDC. it also has an output for “external “SR” radio”. Whatever that may be.

It works well under low volume but at higher volume it starts squealing and with a bit of artistical input you can make it sound like a formula 1 car.

If anyone has more information or is familiar with this problem and knows a cure, don’t hesitate to leave a comment or contact me!

Bontempi BT 805 Keyboard

Saw this keyboard being given away for free so I decided to adopt it before it lands in the wrong hands!

On first sight it looks like the usual 90s era digital toy keyboard with cheezy sounds and rythms, and well, it is. The difference is that Bontempi used to make quite interesting organs. Nowadays they seem to be focussing on actual children’s musicial toys. I can hardly find any information on this keyboard, like date of issue or any manual at all. So I guess I’ll have to reinvent this wheel myself.

The instrument is a little scratched and I saw a lot of hairs and dust inside. Guess that’s what comes with free instruments!

Features

Hardware
– 49 keys (4 octaves), no touch sensitivity or aftertouch
– Limited polyphony up to 4 notes
– Headphone output (1/4″ / 6.35mm jack)
– Power adapter barrel jack input center positive +12v
– Battery compartment (needs a lot of batteries, didn’t count)
– Stereo speaker arrangement
– Separate on and off buttons with audible “alarm” to notify the user if the instrument is still on after a certain time of inactivity
– LED indication of “down beat”
– 6 knobs for “percussion” or “chord program”
– 6 knobs for the selection/programming of features
– 2 volume knobs for master volume, 2 volume knobs for the accompaniment
– 2 tempo knobs to set tempo
– start and stop knob for demo and rythms
– record knob (couldn’t find out how to use it)

Software
– 36 built in sounds of which up to two can be “mixed” which leads to a total of 666 total sounds.
– 24 rythms
– 1 demo song
– Toggle sustain on or off (similar to a sustain pedal on a piano)
– Toggle diffusion on or off (literally no clue, seems to affect the stereo image)
– Toggle reverb on or off (adds a bit of reverb)
– “System 5” which basically means 5 different ways to play chords with the left hand.

Choosing a sound or rythm

The selection of sounds and rythms is code based. At startup electric piano (211) is selected and the lite rock (311) rythm. Pressing the start/stop button starts the rythm and the sound can be played over it.

Sound
To select a different sound, simply enter the new code with the 6 select knobs. For example, pres 2-3-6 for flute. A sound of a drum will play if the entered code is valid.

Rythm
To select a different rithm, also just enter the code with the select knobs. For example, 3-4-4 for classic. If there’s already a rythm playing, it will wait till the end of the bar before switching to the new chosen rythm. The tempo can be adjusted while a rythm is playing with the tempo knobs.

Mixed sounds and functions
By default, the function of the keyboard is set to full keyboard (126) and basic sounds (131). To make use of mixed sounds, we first have to enter the mixed sounds function by pressing 1-3-2 on the select knobs. After that press two codes of the basic sounds in succession to have them mixed. The front panel of the keyboard shows various examples.

Demo
Pressing 1-1-1 on the select knobs will automatically start the demo sequence. For some reason they thought it was a good idea to choose some funky version of the Star Wars theme for this. The tempo of the demo song can not be adjusted and loops infinitely.

System 5

Many electric organs and other keyboards have the functionality to change the leftmost keys into chord control. This means that for example just pressing the C key with the left hand, will result in a C major chord you can play over with the right hand. This keyboard decided to step it up a notch and add 5 ways to implement this chord control.

I could hardly figure out how it works so that means I just need to play around with it some more. I found that one of the systems kills the leftmost octave while turning the percussion knobs in arbitrary chords in the key of C. Another system 5 option makes it so you need to use at least two fingers to hear a chord. How to build these chords, I don’t know.

There also seem to be a way to reassign the chords that get audible via the percussion knobs, but I haven’t figured out yet how to do this.

To escape the odd chord control system 5 when you get desperate and confused, just press 1-2-6 to get the full keyboard back.

Playability

The keys feel a bit cheap and the selection knobs sometimes register twice or keep getting stuck under the panel because it’s all built on the cheap. But besides that it’s a fun instrument to play. Some sounds are straight up garbage while others, mainly the synth ones, are quite pleasing!

The percussion sounds hidden under the 6 blue percussion knobs are trash and for some reason those used for the rythm tracks sound better. Seems like they cut some features that are built into the software but are just not accessible to the user. This isn’t rare or anything, happens all the time in these kinds of devices.

One very odd thing is how the stereo image is created. The percussion sounds come from the left speaker only but when awkwardly trying to play these sound polyphonic, the keyboard sometimes decides to pass one to the right speaker. This isn’t a loose solder contact or anything, just how the thing works.

This becomes more apparent when playing the keyboard keys. The keyboard just randomly decides to send some notes to the left speaker, and others to the right and there’s nothing you can do about it. I thought the “diffusion” control would get rid of this but all that seems to do is emphasize the effect. I mean sure, it gives some sort of funky stereo image but it’s really not desired at all times. For example, when trying to record with a mono 1/4″ cable.

Teardown

Ofcourse, I am wondering what’s happening under the hood. So I decided to screw it open and check! I apologize dearly for the amount of dust and hair in the thing, I didn’t bother to clean it up before taking pictures.

The keyboard consists of two single sided PCBs. One of them for the keys, and the other one for the power, amplifier, knobs and digital circuitry.

The construction for the keys actually looks quite decent. Each key has a spring and uses the usual membrane contacts to register key presses.

Seems like each key is marked and has their own diode (1N4148), probably arranged in a way so combinations of keys dont accidentally trigger keys that aren’t pressed. They also did a bad job of cutting the strip of membrane contacts, I got 1.5 for free!

There are only two ICs on the board and one of them is this DIP-16 stereo amplifier (TEA2025B). The backside of the keyboard says that the whole system is rated for 2W and I suppose most of those watts go to the amplifier. The amplifier drives two speakers of 4 ohms and 5 watt.

Notice how these two speakers are of the same impedance and power but are physically different!

Audio amplifier IC with power input and headphones jack

In the picture above is the audio amplifier visible with the barrel jack input and the headphone jack output. Theres some ferrite (L1, L2, L3) to filter the power lines of high frequency noise. The green connector J4 is used to bring power to the keyboard PCB. The used components are all quite “modern”.

When travelling further down the line, we come across some transistors (C33725). Luckily there are very nice markings of the components places on the component side of the PCB. This is probably the lower voltage regulator for the digital portion of the circuit were moving next.

J3 is the connector that comes from the keyboard PCB. On top are some of the switch contacts visible, or at least, the ones that are on the solder side.

In the topright is the connection for the 3mm LED (D1) that indicates when a rythm is on a “down beat”.

There are many links / wire bridges marked with a W which aids the single sided infrastructure.

Those black caterpillars are resistor arrays or resistor networks. Basically many resistors of the same value in one neat package.

Q21 (the blue dot on the right) is possibly a crystal resonator. The heart of the microcontroller I’ll show next.