Circuit bent Casio MT-65

[Jokeyman123]

I'm not advertising this for sale, but thought might be an interesting item, look at what this guy did to his MT-65, whew! Looks like an early Mini-moog. if this is an inappropriate post, I aplogize in advance, but I'm not selling it, I just came across it looking through Casio stuff and this is am impressive mod (always looking for repair parts and such).

 

https://www.ebay.com/itm/S-CAT-01000-CIRCUIT-BENT-Upright-CASIO-MT-65-KEYBOARD-26-MODIFICATIONS/253872423734?_trkparms=aid%3D777001%26algo%3DDISCO.FEED%26ao%3D1%26asc%3D20160801204525%26meid%3Da9af465e37264f50ab4253a6dec87919%26pid%3D100651%26rk%3D1%26rkt%3D1%26%26itm%3D253872423734&_trksid=p2481888.c100651.m4497&_trkparms=pageci%3Abc822dce-be71-11e8-ad6c-74dbd1806387|parentrq%3A01a133e01660abc11473ba3dfffc1e0b|iid%3A3

[Chas]

S-Cat has circuit bent quite a number of Casios over the years. There are a few videos on YouTube showing what his creations can do. However...

 

...On paper the mods seem impressive, but in practice not many of them serve much use in actual music making. A common theme in the world of circuit bending is just to end up with a glitch machine that serves more as a novelty rather than actually enhancing the machine's musical capability and features.  

 

There is a video by a guy who modified his HT700 Casio, and in the process he expanded and added features that made it far more powerful and useful. I wish we could see more of those creations rather than "glitch" and random electronic noise machines. I'll see if I can dig out the videos on YouTube.

[Chas]

Here is the modified HT700.

 

 

And the same guy except this time a modified MT600 he modified:

 

https://youtu.be/BMi6kqhd_1M

[Chas]

And probably one of the best sounding mods done on a Casio HT filter:

 

 

[Chas]

And here's an S-Cat circuit bent MT68 (same as an MT65, just a different colour case).

 

https://youtu.be/1BCp4HFiWpQ

[Jokeyman123]

I just found my circuit mods printouts for the HT-700, which I had considered a few months ago, but the ridiculous prices on eBay now for the HTs makes it a silly adventure-especially considering an XW could play rings around even a heavily modified anything-i guess the appeal is to get the max out of something that has limitiations-composers tried doing that in the 20th century-creating new muscal forms based upon strict limitations for writing music-12 tone rows, music concrete etc. Now we hack technology, but it is now so advanced that there is little left to hack except the older Casios, suzukis, Technics etc. Years ago, PAIA made a few interesting kits for synthesis-could build modular small circuits for filters, oscillators and DSP effects. Now Teenage Engineering is doing it, but with more advanced digital and I see Korg is offering some modular style synth kits.

 

Then, I start messing with sound creation on any of the recent Casios and am amazed. I'm hearing sounds out of the PX-560 I've only heard up until now on my Yamaha SY-77 (well close although that thing is still a frightening sound-beast but you really have to know your way around AFM design or go through dozens of user created sound libraries to get the really far-out stuff) and Equinox. And I am also impressed to hear sounds that I could only play using my old Ensoniq TS-12-ARP and old Elka Synthex sounds are in there...this is an older arrangement I put together on the TS-12 called Air Guitar which has nothing to do with guitars he..he..I am trying to duplicate some of this old work just to see how close I can get it with the PX560 but this should be another post I guess. I am hearing some of these sounds now in the PX560. Notice the lovely old Wurlitzer from the TS, sounds very much like the new one on the PX560. Drums on the TS-12 are still pretty hard to beat, this is only one kit. No quantize. Ending is not great but I was in a hurry and was going to add another improv on top of the ending vamp. The organ-the Ensoniqs had killer leslie simulators, but the Casio is very close. So there you are.

Air Guitar.mp3

 

Somebody at Casio must be pretty knowledgable about sound design to get all that in there...so I've lost a little interest in modding and hacking....for now!

[CYBERYOGI =CO=Windler]

Most interesting is that the MT-65 sound IC "D931C" can be software controlled. Robin Whittle identified in 1980th the (very counterintuitive) serial data format, so a microcontroller can be hooked to its 4-bit bus to define own preset sounds. Here someone made an editor for it:

https://wolfeffect.wordpress.com/casio-931-chip-editor

[TheDave]

My Mt 68 was covered in battery acid when I got it , took it completely apart to clean it. Totally lost more than a few slider parts but the issues that concern me are about the playability. ....it has little. The drums have stopped working and the volume for the voices are all over the place and it seems to have a distortion when playing chords. Any general advice on where to start looking would be appreciated.

[Chas]

On 8/31/2019 at 12:11 PM, TheDave said:

My Mt 68 was covered in battery acid when I got it , took it completely apart to clean it. Totally lost more than a few slider parts but the issues that concern me are about the playability. ....it has little. The drums have stopped working and the volume for the voices are all over the place and it seems to have a distortion when playing chords. Any general advice on where to start looking would be appreciated.

 

The battery acid is the main concern. Even if you've cleaned everything off, depending on how long the acid has sat on the parts/ board, extensive damage could have occurred. The acid can eat away at the PCB tracks causing all sorts of issues and malfunctions. This is often an issue even with just the back up battery used in old 80's synths, let alone a whole load of C type alkaline batteries in the back of a vintage Casio. Check out the large number of failed 80's Korg Polysixes, which are notorious for back up batteries leaking causing the PCB to get so badly damaged that they become almost scrap.

 

With regards to your MT68, I would get a multimeter and start checking the PCB tracks to ensure that none have been severed by the acid. You should also start checking the PCB components - resistors, capacitors, transistors etc. If any of these were covered in acid, it could have irreparably damaged them causing the issues you have. Another issue is that it can be hard to clean off all the acid as it can soak into the board/ components and will continue eating away at parts, even if you've managed clean most of it off.

 

How much and where exactly was your MT68 covered in acid? Can you share any pictures of the leakage? If extensive, to be honest, you're probably be better off looking for another as it will simply take too long and cost too much to repair. Don't get me wrong, I love the MT68 (I have one and also its twin brother in white - the MT65), and rate them highly for a retro Casio. But if they're badly damaged, unless they have immense sentimental value they're simply not worth spending large sums of money repairing when you can simply go out and buy another for less.

 

    

[Jokeyman123]

I agree with Chas on this-trying to restore a few older non-working Yamaha QY units with similar battery acid damage, i discovered 2 primary problems.

 

1) capacitors-dry up from sitting with no power-current through these keeps the caps working so if the backup battery is gone, and the main batteries are ruined from corrosion, the caps probably went too if this sat unused for awhile. This problem can be solved by replacing-all the caps since it is very difficult to assess a cap, I use a specific capacitance meter.

 

There is an even more daunting problem i learned from other troubleshooters-and Chas has described-the circuit boards can become contaminated-even if the board looks clean and intact-apparently the residual chemicals from the battery acid leaking can penetrate the IC board or boards and cause many problems-conducting where it shouldn't and shorting where it shouldn't. Check the caps first and circuit trace for conductivity to the components-this can be done simply by checking voltage swhen applying power-to see if components are getting power-should be mainly 5V in most ICs, maybe 9-10v in others, I have no schematic for the MT series. If everything looks good-I would start testing caps-a decent capacitance meter can be bought online for about 30-40 dollars, maybe a bit more or less depending on where you are on the planet.

[Chas]

Agree with everything that Jokeyman said above 👍

 

Would also add, if you don't mind stripping the boards down to the basics, you could try using the dishwasher technique. Yes, you read that right, put it in the dishwasher! Apparently it's a known trick for sorting out leaking capacitor goo on old Apple computers. The excellent 8 Bit Guy did an episode about this on his YouTube channel.

 

 

[CYBERYOGI =CO=Windler]

Do not use a dishwasher! The aggressive cleaning agent may dissolve the carbon tracks of potentiometers and carbon paint traces (e.g. at rubber contacts). Of course remove all batteries (also soldered ones - MT-65 contains none) before wet cleaning.

Washing a PCB in bathtub with hand dishwashing soap is much safer. I read that leaving a drop of concentrated dishwashing soap on a battery acid infested spot soak for some hours can neutralise it. Later thoroughly rinse the PCB with freshwater (shower). Dry it with tissues and hairdryer (medium heat). Clean oxidized switch contacts with isopropanol and a cotton swab.

Alkaline batteries are actually alkalic instead of acid (forming white powder and greenspan). Only zinc-carbon had actual acid in it (leaving brown rust stains). Both needs to be removed to stop corrosion.

To search for acid damaged PCB traces with a DMM, particularly look for traces with black spots under the green paint. These are corroded and may be interrupted. Also through-hole contacts between PCB sides or multilayer traces tend to corrode away. Remove paint and greenspan at such spots with sand paper and solder a thin wire across the gap.

[Juandoe]

Well, I hate to revive a dead thread, but I feel like this is going to be the best place to get an answer. I recently picked up an MT-65 and I’m pretty blown away with it as far as a cheap keyboard goes. I love the arpeggiator on it, but the bass lines ruin it. Is there a way I would be able to mod the board to kill the signal from the bass and chord features of the arpeggiator? Preferably controlled by an on/off switch. I’m a noob to vintage synths and circuit bending but I do have a little skill with a soldering iron. 

 

[IanB]

I just found the schematic on Elektrotanya and it looks like you can do this. The Chord, Bass and Arpeggiator signals all sum at a simple inverting op-amp mixer so it looks that it would be pretty easy to just lift the ends of the resistors and attach switches to select any of the combinations going into the op-amp.

 

https://elektrotanya.com/casio_mt-65,mt-68,mt-100,ct-405.pdf/download.html

 

There are a number of copies of the MA1M main circuit board diagram, apparently different revisions,  but the op-amp in question is labelled 81C (it'll be a TL081) and it's in the top section of the diagram feeding to connection CA-4 (they're photocopies and a bit difficult to read, but sufficient squinting should find the part I'm describing).

[Juandoe]

On 10/14/2020 at 12:26 PM, IanB said:

I just found the schematic on Elektrotanya and it looks like you can do this. The Chord, Bass and Arpeggiator signals all sum at a simple inverting op-amp mixer so it looks that it would be pretty easy to just lift the ends of the resistors and attach switches to select any of the combinations going into the op-amp.

 

https://elektrotanya.com/casio_mt-65,mt-68,mt-100,ct-405.pdf/download.html

 

There are a number of copies of the MA1M main circuit board diagram, apparently different revisions,  but the op-amp in question is labelled 81C (it'll be a TL081) and it's in the top section of the diagram feeding to connection CA-4 (they're photocopies and a bit difficult to read, but sufficient squinting should find the part I'm describing).

Wow thank you for the reply and the schematic! I don’t know exactly when I’m going to attempt this, but I appreciate the help. I’ve grown pretty attached to this one already so I might try to pick up another to tinker with. 
 

I do have another question about modding it a little further, but this one might not be as straight forward. 
 

The arpeggiator only has one preset tone and doesn’t follow the tone selected from the bank. Is there a way to route those tones to the arpeggiator? 

[Chas]

13 hours ago, Juandoe said:

Wow thank you for the reply and the schematic! I don’t know exactly when I’m going to attempt this, but I appreciate the help. I’ve grown pretty attached to this one already so I might try to pick up another to tinker with. 
 

I do have another question about modding it a little further, but this one might not be as straight forward. 
 

The arpeggiator only has one preset tone and doesn’t follow the tone selected from the bank. Is there a way to route those tones to the arpeggiator? 

 

@Juandoe- The Mt 65 (and MT 68) are very similar to the MT-400V and CT-410V. The latter lose the arpeggio and a couple of other features (their CPU has them, but they are not connected), instead they gained a genuine analogue resonant filter as well as a stereo chorus type effect. Regardless, the main voice chip I believe is the same, so if you check this link it will show you the CPU matrix and what features it has and how they are connected.

http://weltenschule.de/TableHooters/Casio_CT-410V.html

To answer your question above, I believe that the arpeggio tone is fixed, it is not related to the preset selectable tones. I have an MT65 and MT68, and this is normal behaviour for them. 

I too have wanted to isolate the arpeggio so that I can record it on its own and use it in my compositions. I have tried doing this in DAW software by using equalizers/ filters to cut out the frequencies either side of the arpeggio tone frequency spectrum. However, there is obviously some bleed from the bass line overlapping the arpeggio's frequency meaning that I wasn't able to completely isolate it. It was almost useable, but it would be much better if if it were totally isolated. What I gather from other modified MT65's/ 68's, it IS possible to "circuit bend" them to allow different elements to be switched on and off, including being able to isolate the arpeggio sound. Like you, my MT's are in nice condition and I really don't want to start hacking them about by adding external switches. I would love to be able to add extra controls via a breakout box, and maybe have a connection through the battery compartment. I would love to be able to also disconnect the breakout box from the battery compartment and have the MT behave (as well as look) completely standard.  At some point I may look into doing this with one of my MT's.

@IanB- thanks so much for the link to the MT-65/ 68 service manual! I've downloaded and added it to my archive for future use 👍

[IanB]

@Juandoe There doesn't seem to be a way to change the arpeggiator tone, it comes out of the tone generator chip "ex nihilo" it seems, so you are stuck with it. These chips seem to have been very specifically designed to a specification from Casio, understandable in the days of very limited transistor budgets on ICs.

 

Also @Chas This does appear to be a simple "bend" to isolate the tones, since they come together at one point at the input of the said op-amp. The specific op amp and circuit traces should be easy to spot on a photo of the main circuit board, if anyone would care to post one.

[pianokeyjoe]

I own 2 MT65 keyboards and a parted out Casiotone 405. The mods on these are easy as already stated here, but my resounding question is: how and where to download the MT65 IC editor for Windows 7 and the mod schematics? The link to the blog only shows pictures, but no download links. If anybody has heard of or bought HIGHLY LIQUID UMR2 universal midi retrofit for such keyboards, I would at least need a pdf of how to hook that board up to the MT65/68/405 units. The retrofit is available cheap on ebay but with NO instructions. So I thought maybe the link provided here of the NEC D931C windows editor and wiring mod, would be the ticket. LOL! Neither option is available in 2021 it seems. So how to MIDI up this board?

[pianokeyjoe]

@CYBERYOGI =CO=WindlerHi! I think you are mr Table Hooters guy from Warranty Void website? If so, YEY! I am on an active hunt down for that 931 chip editor software? Do you know where I can get it? And is it for Windows OS? Also, My quest for midi IN for my MT65/CT405 is still active. I found Highly Liquid UMR2 info and SOME hook up instructions on a site called MUFF WIGGLER of all things! Sadly, the following Keyboards are not found for hook up instructions to that midi retrofit board: MT100,MT36,MT52,MT45,MT65,MT205,MT520, and SK2100. These are the keyboards I own and was wondering if you KNOW anything about midi input for these models? The more interesting CPS201 which is a touch responsive non midi electronic Casio Piano model, would be nice with midi as well. Any clue or direction would be great. S-Cat has done it with these models and others of the PT series as well so I am mystified as to why I can not find any instructions in 2021 still.

 

BTW, have you ever released any videos of your stuff from your warranty Void site? To hear examples of the keyboards you describe would be grrrreat!

[CYBERYOGI =CO=Windler]

https://wolfeffect.wordpress.com/casio-931-chip-editor/

 

I have health issuses and was/am too close to suicide to make any videos. It took me a year to mod my PC (Colani bigtower) with a 2nd mainboard to run more things than Win98SE only and still have some 10k unsorted hardware photos, worsening eyesight and my body is rotting apart. 🤢

 

I guess Stephen Hawking would have been a manually more skillful keyboard player than me.

Edited January 12, 2022 by CYBERYOGI =CO=Windler

[Jokeyman123]

Hang in there Cyberyogi-you are needed, here and I am sure elsewhere. I had surgery on both my eyes this past 2 years (took that long) and then my eye surgeon passed awy-from Covid, but he was restoring people's sight right up to, I was devastated, was a wonderful brilliant man. Remember the words of the Billy Joel song "angry Young Man" which I was before I became an angry old one "I found that just surviving was a noble fight".  OR....

"Growing old is not for the young"-quote from Jokeyman's toolbox of very limited wisdom.

[Joe Muscara]

OT but I hope you are okay, Cyberyogi. Please take care of yourself and get any help you need. We care.

[Brad Saucier]

Yes, please take care of yourself.  If you haven't already done so, please seek help from someone with experience.  They can help tremendously.

[IanB]

To echo others, please look after yourself. The rotting that comes with ageing is the dark part of the human experience sadly. I hope you will start to feel better soon, we are all with you here.

 

The project looks amazing! May I ask what that little USB board is? I presume it's some kind of converter to talk to lesser microcontrollers?

[pianokeyjoe]

Aww! @CYBERYOGI =CO=Windler! I am sorry to hear that you are going through troubles like that. I myself am in a dark place that only the LORD can bring me out of. But we are here if you need us and yes, we do care! I remember you website from years ago and I really started collecting Tablehooters as you called them! Fine work my friend! God bless!