Ra226

Funny you should ask, I've got a working Arduino-based emulator going right now, just about ready to launch. My goal is to be able to scan books into code, then play the same code back out the emulator. It will also be able to play back home brew tunes (calculating the checksum automatically so the composer won't need to). I'll share here when it's ready for launch, which I'm hoping will be in about a week.

There are so many things you could try, it's hard to say where to start. You might check the electrolytic capacitors, those can often die after many years and that can be a common problem in old electronics. Specifically look to see if they're expanded and/or leaking. Maybe take an oscilloscope to the CPU's clock pins, and then the other CPU pins to see if the CPU is at least doing anything?

Hi, all--I'm bringing this thread back because I've managed to fix the issue by doing exactly what I theorized earlier: removing LSI-1's DAC, swapping the chips, and connecting the serial lines. The bad chip is now in LSI-1's position and does not output any audio via the audio out pins, sending it instead as data over the serial channel to LSI-2 (which is now the good chip). The only drawback to this solution is the Accomp. Volume control no longer controls the chords/bass line (but does still control percussion). I consider this to be pretty minor and am very happy to have a fully playable MT-70 now! Problem If you have an MT-70 that's playing 3 or 4 good notes followed by 3 or 4 bad notes, it's possible you have a bad output stage on one of your LSI chips. If chords sound bad, it's LSI-1 that's bad. If chords sound good (which was my case), it's LSI-2 that's bad. Solution Either way, remove the DAC from LSI-1 and disconnect the resistors at pins 23 and 24 on LSI-1. Then: If LSI-1 is bad: wire the two LSI Pin 9's to eachother, and the two Pin 11's to eachother If LSI-2 is bad: swap the two LSI chips, then do the wires as above See picture, and be careful of solder bridges. I accidentally tied the CLOCK signal to 5V (pins 20 and 21) on one of my LSI's and the keyboard locked up on me.

I would love to see that--the page has the links to the board from OSHpark but there would still be soldering (but no etching) involved. If you don't have an Arduino Pro Mini to solder up, you could probably order the board, mount it in an RO-551 (that's exactly what I did), and then wire it to a different Arduino. There's also a discord set up where a few people are starting to do things. https://discord.gg/uwvRWgQhSK

Hi, all! Details on my site, but I wanted to share hardware specs and code for dumping and playing back ROM packs via Arduino. I've also got the code figured out to the point where it's possible to make new ROM packs. https://ra226.net/casio-rom-emulator-ro-226/ In recently launching, I've learned I'm not the only one working on this, but information out there is still very sparse. I'm hoping to change that and would love to see home brew ROM packs happen. Questions, comments, fire away!

According to CT-701 textbook, you are correct: 9, 10, and 11 are DAD, SYNC, and EVD, respectively. That doc also defines pin 18 as MSO, Master/Slave select. According to the CT-1000P Service Manual schematics, SYNC is directly connected between the chips, and DAD and EVD are connected through switches (4066 chip). The diagram shows the Melody LSI as master and the Accomp (chords) LSI as slave, and data flows from slave to master. The schematic shows MSO (pin 18) connected to Ground on the Accomp LSI, so I'm going to assume connecting MSO to ground is what determines slave (and therefore sets the data dirction on DAD/EVD). On the MT-70, LSI-1 is the slave chip (MSO pin is connected to ground) but DAD/EVD are left open (see the photo of the digital board). SYNC is still connected between the two. On LSI-2, DAD/EVD are connected to Vcc via 47k resistors (probably just to keep noise from being treated as an input signal). So for whatever reason, it looks like they elected not to use that digital channel on the MT-70. Now I'm kind of curious what would happen if I connected DAD/EVD... A workaround for my LSI-2 chip with bad outputs might be to swap the two chips, put the bad one in LSI-1's position, disconnect the LSI-1 DAC, then connect the DAD/EVD pins. In theory, non-chord mode would work with 8 fully-functioning polyphonic notes instead of the 4 bad/3 good. Chord mode would send the chords through the other chip and also work, but there'd be no way to control the volume on them. I'm not sure I want to do that much soldering and de-soldering, but it's fun to think about.

Yes, the 4066 (at D4 on the Analog board) has two switches being used, always in opposite states (their inputs are TIM-0 or inverted TIM-0--line 7 on the ribbon cable). They take in the audio from LSI-1 and route it to either the Op Amp right above in non-chord mode (where it's mixed with LSI-2's audio) or to the filter block, etc, where it's mixed with the percussion, sent to the Accomp volume control, etc... I love what you mention about this chip--how it's almost like an alternative future that never was. There's some advanced stuff going on and it really looks like they wanted this to be the future, but then they decided to go a different route. What a great idea to look up the patent, I'll have to go find that, it sounds interesting.

If that were the case, wouldn't all the notes sound bad or all the notes sound good when in non-chord mode? Also, I've definitely confirmed by listening to the outputs of both DACs that even in non-chord mode, both chips send their sounds analog, through their respective DACs. I'm not sure why they didn't take advantage of that digital passthrough like the 701 does.

@Macola I don't think I quite know enough about the digital board to answer that one. There's a lot of good data on the CT-701, but it's different enough from the MT-70 that it's only so helpful. I'd start with the CT-701 Textbook. I found the CZ-101 service manual useful, too (it had several schematics), but mainly for the analog portions. It might be the Schmitt circuit (section 7.4 in that document), but hard to say. Also, feel free to piggy-back, I was hoping to just get more info on the MT-70 out there.

Hi @CYBERYOGI =CO=Windler I was hoping you'd chime in here--I'm familiar with the thread you quoted, and their problem was very similar to mine. I considered just adding my issue to it, but I don't believe the MT-70 works the same way. On the MT-70, both LSI chips have a DAC, the outputs are sent to the dual-op amp (bottom center) then sent out the ribbon cable to the analog board. Still, I'm pretty sure you're right about the chips being identical. Keen On Keys (fantastic youtube channel) has torn down an MT-70 and his chips are identically labeled. I could probably desolder both my chips and swap them to be absolutely sure, but that seems like a lot of work to still have a broken keyboard afterward! I think Chas is right, I'll just have to wait for a suitably-priced broken one to show up. Meanwhile, here are my photos of the digital board and my conceptual diagram of the Analog board. Hope they're helpful to anyone trying to troubleshoot one of these.

Hi, all. New to the forum--I recently purchased an MT-70 which unfortunately is not completely working. I was told it was being sold as is for parts, so fair warning... but I'd hoped it'd be easier to fix. Turns out I have a bad LSI-2 chip. I was hoping it would be any other part, but I'm afraid it's not. So the short version of this post is: anyone got a spare LSI-2 chip from an MT-70 or ideas where I might get one? My only thought is to wait for another to show up for parts (but then I'll be stuck with an extra pile of not-working MT-70). The long version of this post is that I actually had a lot of fun analyzing this keyboard and hoped that my work might be useful to anyone else attempting to fix one of these. My symptom is the first through fourth notes played sound like garbage. The following three sound fine, then the pattern repeats. Or, if in chord mode, the accompaniment sounds fine (bass and chords/arpeggio), and any other notes played do not. This problem is similar to a few mentioned in the CT 701 thread in this same forum. My initial guess was, due to the way it sounded, that the sample and hold circuit was bad, failing to to elliminate the noise. Before taking a closer look, I figured this would be an electrolytic cap which can have issues. As it turns out, those caps are tiny 0.01 uF ceramics and this was not the problem. And also, the sound before the S&H circuit doesn't really sound all that different. Working my way backward, I next had a look at the DAC. I really doubted this would be the issue since it's just a resistor network--sure enough, it was not. Having removed the DAC, that left the pins on the chip itself open, which turned out to be the problem. Under oscilloscope, LSI-1 has nice, square outputs. LSI-2 does not. Attached to this post are several pictures of the analog board (where I originally thought the problem was). I've mirrored, resized, and overlayed the back of the board on top of the front so you can easily trace signals. I have not been able to find any kind of service manual or schematic for this keyboard. There is a CT-701 "Textbook" document out there, which was very helpful, and the CZ-101 service manual does have several circuits in common with the MT-70. Other discoveries I made about this keyboard as I went through analyzing it: LSI-1 is "Master." It provides bass/chords when needed. LSI-1 and LSI-2 have different suffixes on my specimen. LSI-2 is 43617 13, LSI-1 is 43617 23. Maybe they're not identical? (I'm guessing some ROM code?) DAS2 not used in MT-70 DAS circuit much simplified compared to CT-701. No discrete transistors, only NOR and bilateral switches. D/A Shift is really "Expander" (see CZ-1000 docs). Increases dynamic range D/A Shift and S/H circuits somewhat combined. One dual Op-Amp accomplishes both. White Noise source is quite different from CT-701. Op-Amp-based source serves high-hats and snare Snare signal runs through 555 timer. Presumably monostable, to lengthen pulse for noise portion Drum signals are different than CT-701. No congas, and use different lines. LSI's from CT-701 likely not compatible with MT-70. Voltage regulator is just plain old power transistor. Warms up a bit, rather inefficient. Each chip has a 10-bit DAC despite being 12-bit, with lowest two bits made from discrete resistors DAC is typical R-2R, with R-25k. The LSB does not have a 2R, though, so it was designed to have more bits added onto it. The green arrows trace the raw LSI-2 analog audio signal from the digital board to the Expander, S&H, and into the audio mix. LSI-1 audio (not shown) follows a similar track, but optionally gets routed through the accompaniment system (when in chord mode) so the accomp volume dial can control it along with the percussion. Both are combined in Master Mix, then sent to the main volume dial, then to the power amp. So I hope this is useful to someone out there--and if anyone can hook me up with an MT-70 LSI-2, I'd be grateful!