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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!