CYBERYOGI =CO=Windler

In my Casio CT-810 (from eBay in very poor condition) I had to remove, dismantle and clean every single potentiometer to make it sound again. To clean the carbon track, use isopropanol and a cotton swab. NEVER use contact cleaner spray - it is too aggressive and will dissolve the carbon track. If the carbon track of a potentiometer is worn through, you can fix this by coating it with a soft pencil (the retractable fine type is more precise than wooden ones) until the resistance value is ok. If you accidentally short nearby traces, remove the unwanted pencil line with cotton swab and isopropanol. Pencil graphite may be less scratch resistant than the original material, but with unobtainable special (e.g. slide) potentiometers it is better than nothing. If a rotary potentiometer makes shaky contact or crackles badly despite the inside looks clean, try to clean the (often tiny and badly visible) metal-to-metal contacts. If they are hard to reach and can not be dismantled, insert a tiny strip of paper between contacts and turn the pot a few times to remove oxidization. If the bolted lead at the carbon track end makes bad contact (and can not be tightened mechanically), you may apply some conductive silver paint. This also helps when given conductive metal coating has corroded or burnt away (by overload or humidity).

You don't need new keys (unless they are missing). Simply take it apart and hotglue the key with a piece of sheetplastic (from PE/PP blister packaging) back to the strip.

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.

Perhaps one of the sound chips is broken, so every n-th note will fail only when the keyboard uses all 3 for mainvoice. The hardware can digitally daisychain multiple of them to avoid analogue mixing, which may complicate the situation.

I have here the MZ-2000 service manual PDF. The sound engine seems to be built around 2 big SMD chips "UPD914GM-3ED", one acting as "DSP (Effect)", the other labelled "Sound Source ROM". The only filter I see in the block diagram sits between DAC output and volume pot to the amp, so I doubt that there is a VCA. There are adjustment procedures mentioned for aftertouch (has a trimmer) but none for VCA either. So I suspect it is purely digital, despite there was a time when "analogue" was demonized as something outdated that had to be overcome to manufacture state of art technology and so might get camouflaged. But much like in MT-540, all audio processing and mixing seems to happen before the DAC and hence is digital. "polyphony: 64 notes maximum (32 maximum for some tones)" This looks sufficient to avoid hanging notes. The selftest contains plenty of keys, controls, midi and diskette drive tests, but nothing about filters. The Casio MZ-2000 is claimed to contain real mask roms combined with several sram connected in various places to individual main ICs, which looks much safer than the modern flash memory disease that stores firmware and user data in the same overwriteable chip that can die of bitrot at any time when a tiny power surge or removal of supply voltage makes wear levelling go wrong or has none anyway to make the chip wear out by planned obsolescence once warranty has ended. But there are 2x 4M-bit static ram backed up by a lithium battery. Once it drains, this may cause strange things when e.g. stored synth parameters go nuts. E.g. my Yamaha MK-100 stores all settings in battery backed up RAM; with no batteries inserted the RAM is still backed up by a large electrolytic capacitor for a few days(?). When the cap runs empty, this messes up the data badly and even causes things to subtly malfunction those normally were expected not to be RAM dependant. E.g. sometimes particular preset sounds plays too silent or certain parts of them refuse to be editable, or their LEDs show mess or sustain doesn't work or even the chord volume slide switch refuses to change volume at some positions (e.g. only 2 of the 5 positions have different volume). These flaws can drive you crazy and make you take the entire thing apart for hours to successlessly search for dirty switches etc. etc. and even in the manual I downloaded from Yamaha there is no reset procedure for this keyboard explained to prevent this. To fix this, I finally installed a reset button switch to clear memory.

Symphonytron 8000 uses regular D931C soundchips (consonant-vowel, controlled by external CPUs). Casio CT-6000 and CPS-201 are AFAIK the only instruments using the Music LSI "NEC D932G" (64 pin zigzag DIL) that supports velocity. I wrote in this thread about it. The technical details of D932G are mostly unresearched. The next Music LSI chip number D933AC was already phase distortion used in the CZ-series.

MT-65 uses a CPU with separate soundchip. The M10 has single-chip hardware (D77xG family). The "NEC D77xG" (64 pin zigzag DIL) was Casio's first polyphonic keyboard CPU that was used until 1981(?). It contains a keyboard matrix decoder with 4 quick access memory settings for favourite preset sounds, those are normally selected through keyboard keys + select button, but this selection method can be also simulated by preset sound buttons connected through logic ICs (like in Casiotone 401; pulling pin 34 hi seems to mute the demo note). The sound generator is 8 note polyphonic with digital envelope and stair shaped waveforms those sound much like multipulse squarewave. The 14bit digital audio output is fed into an external resistor ladder DAC. Each sound is made from 2 layered subvoices with independent envelope, what Casio called "Consonant-Vowel-Synthesis". It can additionally select timbres through an external analogue filter circuit controlled through 8 digital switch outputs. 2 of these CPUs with different software number can be wired parallel (one polls the keyboard matrix while both read it) to produce more complex layered preset sounds (4 subvoices using 2 filters). The tone scale can be switched from normal chromatic to a slightly spread variant which produces a chorus effect when 2 layered ICs set it differently. Clock can be input at pin 37 and output from pin 35 (half speed) daisychained to another CPU, or pin 35 is used as input. Bizarre is that this special CPU contains an LCD display port that is not used in any Casio keyboard (nor would it make sense in LCD pocket calculators due to size and power consumption). The CPUs in my 201 run a little hot - possibly because the digital supply voltage has 5.2V instead of the expected 5V and the analogue supply voltage is even 6V. In Casiotone 202 both have only 5V. The naming convention of this earliest Casio keyboard CPU family is horrible; instead of software numbers the main number increases without any logical structure. It may be that advancing the 2nd or 1st digit reflects envelope algorithm changes or size of internal memory, but it also may be simply derived from the release date. According to Robin Whittle, all these ICs seem to differ only in their preset sound set and subtle changes like whether they can do sound selection without playing a demo note. He later called the hardware family 'Series I', but I prefer 'D77xG' despite it contradicts the naming in later keyboards. CPU number hardware class notes & features D771G Casiotone 201 layered with D772G D772G '' (cpu 2) D773G Casiotone 301, 401, M-10 D775G MT-30, MT-40 D776G Casiotone 403 (old) later version has D990G D788G Casiotone 202 layered with D789G D789G '' (cpu 2) D990G MT-60, Casiotone 403 (new) bugfixed D776G? Like with most special Casio ICs there are no datasheets online, but with modern NEC ICs the prefix D77 is used e.g. for 16 bit fixed point DSPs, D78 for generic microcontrollers (like D7811G) and D990 can be digital codecs, so it even may be that these CPUs are (e.g. by Allen's patent lawsuit) internally completely different and only share their pinout. But the very similar sound and behaviour of affected keyboards make this unlikely. Modern NEC IC types have a huge variety of variants and their numbers are longer, so it may be that in 1980 the naming convention did not exist yet and diversified during the following few years which resulted in changing prefix numbers within one family.

Eons ago I fixed a Casio KX-101 which drive is more complex (has motors instead of manual switches) In cassette recorders often the rubber tyres on friction wheels get hard. The wheels itself are plastic, and the rubber rings on its rim can be pulled off. Cleaning their rim with isopropanol may help. Also the bearings may need a drop of isopropanol (never other oil, which can decomposes rubber and various plastic sorts).

I had added some info here.

This might be a keyboard matrix (or LED matrix) scanning signal leaking into audio by a broken capacitor. (I don't know the actual scanning frequency of this model.) This is some 401 info I wrote for my site: The Casiotone 401 uses the main voice CPU NEC D773G, which is an early member of the D77xG family. The accompaniment CPU "NEC D8049C 084" is an MCS-48 microcontroller with 2KB ROM (I dumped it) that controls through I/O IC NEC D8243C the chord section tone generator "Texas Instruments TMS3615NS", which is socketed by unknown reason. Because Casiotone 301 (same hardware without accompaniment) came first, it may be that a shortage of that IC prevented finishing the 401, so the TMS3615NS could be installed last when the rest was already completed. Someone e-mailed me that in his Casiotone 701 the rare DAC IC "AM6012PC" died and that he successfully replaced 2 of them with the modern type "Analog Devices DAC312". It is unknown if these generally suffer of ageing, but another e-mail confirmed that they tend to die. The 401 has the same part connected with its main voice CPU, while the direct successor Casiotone 403 already had the DAC hybrid "EXK-SIOL0025C" (12 pin SIL) - possibly to improve reliability. The 401 is quite heavy (about 10kg?) because despite its case looks almost perfectly like wood, it is mainly made of plastic coated sheet steel. (Casiotone 201 and 202 were of genuine wood.) In spite of this it is not as robust as it appears, because at the corners of the side pieces (made of pressboard?) the plastic woodgrain tends to peel off. I had to hotglue mine back into place, but this sheet plastic stuff also cracks off easily when accidentally folded to hard. I bought my specimen in very dirty state; the whole case was severely sticky especially at the bottom. I am not sure whether it was fatty kitchen dirt or if anybody had tried to apply furniture wax on the case despite it is not of wood. I removed most of that gunk with a paper towel and vegetable oil (stay away from rubber parts) followed by water with dish washing soap, but it still feels sticky on hot days. The high quality speaker sits in an own thick plastic compartment of that even the cable hole was sealed with glue to turn it into a perfectly closed box. It is driven by a large hybrid amplifier module that is screwed to a sheet metal heatsink welded to the case bottom. This makes it very unpleasant to remove the mainboard because you have to unscrew the module and mess around with (possibly poisonous) old heat conductive paste. The dirty speaker grill had to be removed also for cleaning, because someone spilled cacao or similar on it. Be careful with the 5 metal lashes with screw holes those hold the rear part of the control panel from inside. With case opened, these lashes are sharp as razor blades and easily damage the panel and PCB traces; with mine a preset sound LED failed by an accidentally cut trace after working on the opened keyboard. After soldering the trace I glued ribbon adhesive tape over the sheet metal lashes to make them less dangerous. After opening, a lot of broken small black rubber rings fell out of the case - likely they belonged under the piano keys somewhere for damping (keys feel a little loose), but turned brittle by oily room air or ozone. The quite complex analogue hardware of this instrument has the size of an old style PC mainboard and contains many discrete components for the analogue percussion. The percussion have individual trimmers for their decay time. The main IC numbers and sounds have some similarities with the smaller Casio MT-40. The power amplifier is a quite big hybrid module. Unusual is that the fingered chord is up to 12 note polyphonic with additional monophonic bass, while the main voice polyphony is only 8 notes. I don't have a service manual of the 401, but got a photocopy of Casiotone 403, which was of great help to understand the general hardware architecture, because it has the same accompaniment hardware combined with the main voice section of Casio MT-60 (first 403 models had CPU version D776G with external bugfix circuitry). They are a good didactic example how Casio in early instruments made several different CPUs cooperate and combine their keyboard matrices rather than the centralized master-slave approach found in later hardware, and how despite almost self-contained CPUs often minor functions like clock rate conversion or preventing wrong key press order during preset sound selection used a crazy amount of "glue logics" ICs cluttering up the mainboard. The microcontroller based bass accompaniment with tone generator is described in US patent 4561338. There it uses for each 2-bar bass pattern 16 ROM addresses (4 bit) with 5 bit bass note data (31=silence) and 5 bit percussion data (1 bit per sound). When during 2nd bar any chord key is pressed or held, the 4th address bit of the bass note counter resets and so repeats the 1st bar. The accompaniment CPU outputs a monophonic squarewave tone and trigger pulse for the analogue bass envelope circuit, and trigger outs for analogue percussion. In the actual instrument it also controls the chord tone generator TMS3615NS through an I/O IC. Danger!: The IC TMS3615NS employs a +15V high supply voltage, which may destroy other ICs when accidentally shorted. Thus stay away from pin 4 and do not blindly poke around in the circuitry; also some logic ICs use this voltage.

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

That's because the main voice CPU supports fewer keys than the MT-45 keyboard has. (It would support only 1 lower and 5 higher note keys, because it was designed for shorter keyboards like MT-11 and PT-7.) The electronics of the MT-45 employs the same very versatile D930G accompaniment CPU like the Casio CT-410V (and many other Casio instruments), although here only few features of it are used. Unlike in many other Casio keyboards, it is here not combined with the versatile D931C main voice soundchip (that it was dedicated for?), but a foreign main voice CPU "Hitachi HD44140" (same like in the rhythmless Casio MT-11) with only 8 preset sounds. Unlike the D931C, the HD44140 does not communicate at all with the D930G, but uses a completely independent keyboard matrix for all main voice related keys and switches. (Possibly Casio had not finished the D931C yet when the MT-45 went in production.) Unfortunately this results in that the accompaniment section at the left half of the keyboard can not be switched off, thus these keys can not be used for main voice play when neither chords nor manual bass is wanted. The only benefit is that so the polyphony is not reduced by accompaniment. But the HD44140 supports only 37 keys anyway, thus in a 49 keys instrument it would make little sense to circumvent this by complicated external logics. To the right of the HD44140 is a trimmer that seems to be the level adjustment for the highest main voice bit. Another trimmer to its left was omitted (empty solder holes), that was intended to tweak the level ratio between low and higher bits to minimize distortion. The trimmer even further left seems to set the main volume. On the amp PCB there is a section of unused solder holes those look like made for a sustain pedal jack (not supported by HD44140) or tuning trimmer (not used due to crystal clock); its 3 unused foil cable solder pads go into nowhere. The MT-45 has 2 strange black square crystal oscillators. That at the D930G has a "6596, KSS3B" (PCB mark "X1 (6.6M)"?) while that of HD44140 is printed "5752, KSS3A" (PCB mark "X2 (5.7M). So I guess that the upper number is the frequency in kHz. Casio likely used crystals here because else it would have been hard to keep D930G and HD44140 play in tune with each other, because their clock ratio of 1.14673157163:1 would be hard to produce by simple frequency dividers. rhythm & accompaniment About the rhythm and accompaniment section and the tons of hidden D930G eastereggs (see CT-410V).

Casiotone 701 is a relative of MT-70 and uses the same soundchips like Casotone 1000p. This chip even has the crazy capability to daisychain digital audio from an identical 2nd chip to omit analogue mixing (which was unique in such early casios). This is some text I wrote for my keyboard site: The MT-70 was derived from the fullsize Casiotone 701, which has a 3rd HD43517 sound IC to support 8 note polyphonic play in chord mode, and a 3 digit 7 segment LED display instead of LCD. The general hardware architecture seems to be in US patent 4534257 (describing a CPU controlled keyboard that strongly resembles the 701, priority date 1981). The Casio barcode data format is described in the US patents 4422361 (general) and 4437378 (with key lighting). According to US patent 4464966 Casio also planned barcode programmable rhythm, which AFAIK was never released. The sound IC is explained in the Casiotone 1000P patent (US patent 4538495) and further details in US patent 4453440, which describes digital envelope control by adding phase shifted copies of the same sine wave to avoid multiplication, and how overtones are produced by a kind of phase distortion predecessor. In this patent Casio also describes how to mix the outputs of multiple sound ICs digitally, which was never done in any other 1980th Casio keyboards I am aware of. The sequencer is in US patent 4876938 (autoplay) which also mentions this sound IC. US patent 4622879 reveals the sequencer edit algorithm. I haven't analyzed the hardware further yet, but Robin Whittle wrote (slightly desperate) in his technical bulletin "Modifying the Casiotone Instruments" from 1981 about this hardware family: "The Series III instruments are the CT-701, 601 and 501, the 1000p and the MT-70. [... They] use a Z-80 like microcomputer - and two or three identical 42 pin Hitachi chips to produce the sound. The computer scans the keys, organises everything, and talks to the Hitachi chips via an 8 bit data bus. The Hitachi chips produce 12 bits of digital audio with a 25 Khz sample rate and control an attenuator which follows the DAC. Each chip produces 4 waveforms which are composed of variable amounts of the first 8 harmonics, the levels of which can be changed in each channel in real time. It is impossible to make the computer run another program. Bypassing the lowpass filter gives a brighter tone, but adds to the already unacceptable noise level. I have had little success in getting rid of this noise - it seems to come from everywhere and therefore I cannot see much point in trying to do anything more with these instruments." When we compare that 25kHz mixing frequency and 12 bit with the 500kHz (see here) and up to 17 bit of the great D931C, it is no wonder that the HD43517 sound IC sucks. Like its competitor Yamaha PC-100 (and unlike previous Casios) the HD43517 sound engine has no switchable filters for different preset sounds anymore, which makes dull tones prone to digital noise and any static noise filter against it muffles bright tones more than desired. Apparently it was a crude attempt of imitating a Hammond organ or Yamaha's dull FM sound style, but it rather sounds cold, hollow and hissy and is way less versatile. It would be interesting to know how Z80-like the NEC D7802G really is (1000p has a "D7801G 077"). I expect it to be rather a predecessor of the documented D7811G. Whittle's above description is quite ambiguous; I am not really sure if he meant that each sound IC had per polyphony channel 4 drawbars of each a fixed waveform sample that (in the factory) was made from 8 premixed sine wave harmonics, or that each IC had 4 polyphony channels with each 8 sine wave drawbars. The US patent 4538495 reveals that none of these seem to be true, but genuinely the readout phase angle of a 12 bit sine wave ROM is multiplied with a periodic signal from a CPU controllable "harmonic control section", which appears to be a crude predecessor of phase distortion. Said section uses binary gate control signals {XS0, XS1, XQ, Y0, YS2, YQ} to selectively multiply the phase data and/or phase address with 2 or a previous sum and add the result to the sine wave readout address. Frequency- and phase data resolution is 20 bit. Instead of multiplying the output waveform with an ADSR envelope, it is added to the phase data of the sine wave ROM (US patent 4453440). The sound generation for the 4 polyphony channels is time multiplexed (summed at the end as a 12 bit DAC output value), so all register contents of the sound IC is stored in circular multi-bit shift registers. As a form of hardware multitasking, after processing each channel they cycle to the next entry. (The famous D931C sound IC functions similar.) The 7 bit envelope data shift register has instead of 4 even 20 stages, which means 5 cycles per polyphony channel, during those overtones are summed by switching the harmonic control section signals. The sound IC architecture suggests that the envelopes of all 5 harmonics may be programmed individually. With my Casiotone 1000p synth (same sound ICs, I read the service manual) each of its preset timbres consists indeed of up to 5 fixed harmonics (layered sine waves). While its preset volume "envelopes" affect all of them equally, a 2nd kind of preset envelope named "modulation" changes the volume envelopes of (apparently up to 3) harmonics individually, e.g. to imitate a short filter sweep (wah effect) or increase bass or treble amount along the keyboard to approximate lowpass or highpass filtering. But no matter how exciting this additive synthesis thing looks in theory, in real life it sounds just like a sterile drawbar organ that lacks any grit and distortion because fake filters add no overtones. This sound engine is the absolute antithesis of POKEY - smooth and shiny and free of any rough intentional noise. I also suspect that the harmonics have not independent envelopes but that every preset sound has only one envelope with few steps between those it crossfades the vector of harmonics (i.e. waveform), i.e. all overtones change in the same time slots which limits expressivity. pinout HD43517 The Music LSI "Hitachi HD43517" (42 pin DIL) is a 4 note polyphonic sound IC based on additive synthesis, that became famous by the synthesizer Casiotone 1000p. Each polyphony channel is mixing 5 harmonics (sine waves) with different digital envelopes in a similar manner like a drawbar organ. The IC outputs 12 bit digital audio to an external DAC and (like the later D933) 3 additional highest DAC bits control an expander circuit (sort of fast switching VCA, US patent 4414878) to increase dynamic range. (Without expander the DAC waveform tip looks sunken in like a collapsed copula and sounds distorted.) A sample & hold circuit then removes high frequency components. Interesting is that the IC can route its output as digital audio into another HD43517 for digital mixing through thats DAC to simplify analogue wiring. Unfortunately this wastes another DAC bit, and with only about 25kHz output frequency (due to the additional summing of 5 overtones per channel) the specs and tone quality are inferior to the earlier D931C. Interesting is that the internal signal processing (US patent 4453440) already resembles phase distortion, using phase-shifted sine wave addition from a 12 bit lookup table for fast multiplication. Frequency- and phase data resolution for each overtone is 20 bit, with 7 bit envelope controls. Multiple HD43517 (up to 3?, existing in Casiotone 701) can be controlled by one CPU on the same 8 bit data bus. Normally each sound IC outputs audio through its own resistor ladder DAC, but in master-slave mode they can output through the DAC of the master. For this the signals DAD (serial sound data), EVD (envelope data) and SYC (sync) are sent from slave to master sound IC. (The slave's DAC has to be muted externally - e.g. by its sample & hold stage.) DAD and EVD are disconnected to select normal mode. This pinout and description is based on the Casiotone 1000p service manual with its handwritten schematics and incomplete numberings. E.g. the order of DAD and EVD are impossible to see. Apparently all "O-#" pins are outputs, "I-#" are inputs and "IO-#" can be both. pin name purpose 1 I-13 DB0 data bus 2 I-12 DB1 data bus 3 I-11 DB2 data bus 4 I-10 DB3 data bus 5 I-9 DB4 data bus 6 I-8 DB5 data bus 7 I-7 DB6 data bus 8 I-6 DB7 data bus 9 IO-1 DAD ? 10 IO-3 SYC (?) 11 IO-4 EVD ? 12 I-1 CS 13 I-2 /WE (write enable in) 14 I-3 /A/D (adress/data in) 15 O-19 (at 2nd sound IC wired to cpu INT1) 16 O-20 (at 2nd sound IC wired to cpu INT2) 17 I-4 (possibly chip id 2?) 18 I-5 chip id? (at 2nd sound IC wired to GND) 19 I-14 /reset 20 PG clock in (4MHz) 21 Vss supply voltage +5V 22 O-13 23 O-12 digital audio out (LSB) 24 O-11 digital audio out 25 O-10 digital audio out 26 O-9 digital audio out 27 O-8 digital audio out 28 O-7 digital audio out 29 O-6 digital audio out 30 O-5 digital audio out 31 O-4 digital audio out 32 O-3 digital audio out 33 O-2 digital audio out 34 O-1 digital audio out (MSB) 35 O-18 expander control out 36 O-17 expander control out 37 O-16 expander control out 38 IO-2 SH 25kHz out for sample & hold circuit 39 O-14 40 Vcc2 (wired to Vcc1) 41 Vcc1 GND 42 O-15

A shortcircuit (e.g. inside the audio poweramp IC or a really bad electrolytic cap) may also overload something and so force the PSU to turn off. Check if components get hot inside. Measuring the current at the PSU output may also help to identify if anything is shorted.

What do you mean with magneto-optical? An MOD disc is a sort of rewritable CD that was rarely used for anything else than Steve Job's "Next" workstations and CT/MRT imaging computers because they were too expensive for home use. https://de.wikipedia.org/wiki/Magneto-Optical_Disc Almost all 3.5'' diskette drives in computers (Amiga, ST, PC) were beltless (direct drive). AFAIK belts were used only in early 5 1/4'' (cardboard) floppy drives for Apple II etc. With the LCD check the supply voltage of the driver chip with an oscilloscope. If there is much ripple when cold (due to its own spike-shaped power consumption), likely a cap is bad. Naked LCDs also don't like DC offsets on the control voltages (they can decompose the liquid crystal). If through a broken cap leaks DC into control waveforms, it may make the LCD go nuts. LCDs typically are driven by a 4 level stairwave signal. In early hardware (e.g. Casio VL-5) the 4 voltages for the step heights are externally produced and so may be affected by bad capacitors or shortcircuits by battery leak acid spilled at components.

It depends very much on quality whether electrolytic caps survive to stay unpowered for decades and how they behave by load and heat. Switching power supplies will heat up caps those have too high impedance, hence they need special types (that's all explained on the Badcaps site) and they should be 105°C not 85°C types because the rated lifespan in hours is only related to that temperature and will be hundreds or thousands times longer when kept cool enough. The Fortron AT PSU inside the PC I am typing on is from mid of 1990th and its caps still work flawlessly (However I transplanted it into a case of a newer PSU with more air throughput by a bigger fan hanging underneath.) Otherwise a huge McPower lab PSU bought used on eBay immediately stank apart because a noname blastcap died. Last year I recapped my SGI monitor (22 inch Trinitron CRT) that had plenty of bad small caps inside (impedance measured with a Chinese "AVR Transistor-Tester" clone) while physically big caps were all ok. Size matters, because small ones by smaller contact surfaces have trouble getting rid of heat and produce more heat by higher impedance. Electrolytic caps in low current circuits (e.g. tone or envelope control in audio electronics) can function perfectly despite lousy impedance values, or may simply need some minutes to regenerate. So when an old analogue synth behaves a bit odd (e.g. envelope or LFO waveform wrong) it can help to simply wait a while.

> @Jokeyman electrolytic capacitors last longer when not powered up. WRONG! They even age faster by not using them and so decrease inner resistance because the insulating oxid layer dissolves and becomes conductive. Very similar like with deep-discharged NiMH batteries, this regenerates when powered on for some hours. In high power applications (e.g. inside a switching mode PSU) too long unused electrolytic caps can even develop such a strong shortcircuit that they explode or damage connected hardware when not used for some years. This mainly happens with low grade caps, but with very old caps it is recommended to charge them with reduced current (through a resistor) if they behave strange. When caps go bad by heat of normal use, the device is misconstructed (like in many flatscreen TVs). E.g. the main capacitor in my Grundig 6199 tube amp is still intact despite using it for about 14h/day. See Badcaps.net website for more info.

Shorting + and - at the power supply jack can not have any effect because the internal SRAM backup battery or electrolytic capacitor and input voltage are connected through each a diode. Hence shorting from outside can not reach the voltage stored inside. Many power supplies have somewhat low resistance anyway when plugged out of mains (e.g. due to a power LED or other consumers), hence the diodes are necessary to make SRAM work. Only in simply battery operated toys with no complex memory backup feature it can help to remove all batteries and short + and - inside its battery compartment. I remember that my HP48SX calculator had to be modified with external contacts because after a deep crash it could not be turned on anymore for a day (very unsuited for use at university). I had installed an overclocking addon to make it compute curves or solve equations about 3 or 4 times faster, with the side effect to cause crashes if battery was too empty.

The Casio jargon for sound synthesis engine is "sound source". The different engines have cryptic 2 or 3 letter abbreviations proudly mentioned in ads, but with exception of some professional synthesizers the deeper meaning and inner working was hidden from customers (not even told in service manuals). So many of these may be rather advertisement buzzwords than technologies, enshrouding that they were just minor variations of older sound engines. This list is likely inaccurate, because many old or low grade sound sources were not mentioned anywhere, so I only added them from own hardware examination. Also with modern models (large compressed samples) and pianos I am no expert. The IXA sound source (CTK-1000 from 1993) was the last engine with many classic synthesized sounds (now even with velocity and some editable parameters), although it already lacks the famous (SA-series) program loop synthesis preset sounds with complex algorithmic envelopes. After IXA Casio dropped the use of synthesized preset sounds in favour for long wavetable samples imitating natural instruments, which IMO makes newer keyboards mostly boring. With the HPSS sound source from 2013 (XW-G1 synth) fortunately a new versatile synth engine came out, which however does not fully include older (e.g. PD) synth algorithms. This list is sorted by technology rather than release date. (I can not enter this as HTML table here, so it is a little messy.) List of Casio sound sources: sound source full name 1st use notes & features year plain squarewave ? ML-80 monophonic squarewave (1:1, 100% tremolo) 1979 ? ML-81 monophonic squarewave (1:1) with decay envelope 1980 multipulse squarewave ? VL-1 monophonic multipulse squarewave with switchable fixed filter. 1981 ? PT-20 like VL-1 with obligato + chord/bass voice. 1982 ? MT-11 2 layered bipolar multipulse squarewaves with switchable fixed filter. 1983(?) ? MT-200 bipolar multipulse squarewave with switchable fixed filter. 1984(?) stairwave CV Consonant-Vowel synthesis CT-201 2 mixed stairwaves with switchable fixed filter. CT-201 & 202 layer 2 such sound CPUs with each a filter. 1980 ? VL-5 only 1 stairwave with switchable fixed filter (very different hardware). 1982(?) ? MT-65 programmable CV (sound IC with external CPU). 1983 ? CT-6000 velocity sensitive CV variant (layering 3 sound ICs). 1984 SD Spectrum-Dynamics synthesis HT-series user programmable CV variant with VCF for synthesizers. 1987 additive synthesis ? 1000p additive synthesis (5 layered sinewaves, sounds drawbar-like). 1981 Phase Distortion (FM) PD Phase Distortion CZ-series Casio's FM synthesis variant. 1984 iPD Interactive Phase Distortion VZ-series PD successor with programmable routing. 1988 speech synth ? TA-1000 data-reduced speech synthesis (LPC based?, PARCOR?) 1983(?) sampler ? SK-series lofi sampler (SK-1 has also drawbar softsynth). 1986 ? FZ-series 16 bit sampling synthesizer. 1987 ? SK-60 lofi sampler on different PCM engine hardware. 1996 software based (wavetable + multiple synth algorithms) PCM Pulse Code Modulation various, e.g. SA-series Casio wavetable softsynth on a chip, including many other synth algorithms like FM variants or program loop synthesis. The generic term "PCM" was earlier used for anything sample based (e.g. Casio percussion ICs). 1988 CD Casio Digital ? MT-540 PCM engine version with external 16 bit sample ROM. 1988 Super CD ? CT-770(?) PCM engine version with velocity, effect DSP (external 16 bit sample ROM). AP ? AP-7 PCM engine version with velocity, used in first Celviano piano. 1991 ? VA-10 PCM engine version with effect DSP + Harmony Arranger. 1992 IXA Integrated Cross-Sound Architecture CTK-1000 PCM engine version with velocity, multisamples, effect DSP (external 16 bit sample ROM | last engine with many synthesized classic "PCM" sounds). 1993 A2 A² (A-square) wavetable with sample compression + effect DSP. HL Highly compressed Large waveform A2 successor? ZPI Zygotech Polynomial Interpolation MZ-2000 IXA successor(?) with special sample morphing. 2000 AHL Acoustic & Highly-compressed Large-waveform CTK-4000 HL successor with acoustic instrument multisamples. 2008 AIF Acoustic & Intelligent Filtering System Privia piano simulation 2009 AiR Acoustic and Intelligent Resonator Privia piano simulation 2013 HPSS Hybrid Processing Sound Source XW-G1 PCM engine successor for versatile synthesizer (partially hardware based). 2013

First try to clean the battery contacts if corroded. Use e.g. with cotton swab and isopropanol; if impossible to get, use other strong alc or a bit of water and dishwashing detergent and thoroughly dry with a tissue. Also a corroded speaker switch contact inside a headphone jack can make the speaker fail. If nothing helps, the power amplifier IC or an electrolytic capacitor may be faulty or PCB traces damaged by battery leak (needs soldering to repair).

Casio (see links) has a little messy naming scheme; especially some CT-# keyboards were later released as CTK-#, some SA-# as M-# and various toy keyboards had own names. With early keyboards a by 1 higher number often stands simply for a different case colour variant (e.g. brown instead of white). old keyboards: CT- = "Casiotone" fullsize keys (the first keyboards were named "Casiotone #" instead of CT-#") MT- = midsize keys PT- = "Petite Keyboard"(?) mini keys VL- = "VL-Tone" (named after "Very Large Scale Integration" ICs) early mini keyboards EP- = toy keyboard SK- = "Sampletone" sampling keyboard CK-, KX- = keyboard with built-in radio and/ or cassette recorder DM- = midsize dual manual (only DM-100 known) AZ = keytar (guitar shaped keyboard) CZ-, = "CosmosynthesiZer"(?) phase distortion synthesizers (improved FM) VZ- = interactive phase distortion synthesizers (improved FM) HT-, HZ- = "Spectrum-Dynamics synthesis" semi-analogue synthesizers FZ- = professional sampler (contain also phase distortion synthesis) RZ- = drum computer CPS = e-piano (velocity sensitive fullsize keys) CSM- = MIDI tone generator module DG-, PG- = synth guitar DH- = "Digital Horn" MIDI saxophone newer (sample based) "ToneBank" keyboards: CTK- = "CasioTone Keyboard" expensive fullsize keyboard CA- = cheap fullsize keyboard (no MIDI, only mono?) MA- = midsize keys (MA-1..10 = melody alarm clocks) SA- = small keyboard (up to 37 mini or midsize keys) M- = "Casio Club" like SA-series, but M-10 is much older without samples KA-, PA- = toy keyboard RAP- = "Rapman" DJ toy instrument DJ- = DJ toy keyboard with cassette recorder TA- = toy keyboard with cassette player (only TA-10 known, TA-1 = data tape storage cartridge, TA-1000 = talking calculator) KT- = keyboard with built-in radio, cassette recorder and/ or CD player AT- = fullsize oriental keyboard LK- = fullsize key lighting keyboard ML- = key lighting mini keyboard (or 1980th melody calculator) VA- = "Voice Arranger" midsize effect keyboard (only VA-10 known) GZ- = MIDI master keyboard PMP- = velocity sensitive fullsize keys PS-, PX- = e-piano (velocity sensitive fullsize keys) AL-, PL- = key lighting e-piano (velocity sensitive fullsize keys) AP- = heavy wooden e-piano (velocity sensitive fullsize keys) WK- = "workstation keyboard"(?) velocity sensitive fullsize MIDI keyboard MZ- = professional fullsize MIDI workstation keyboard LD = e-drumkit With fullsize keyboards there may be also some other prefixes but I don't care much about them. Also some other exotic names may exist. A general rule of thumb is that Casio instruments with names ending on "-1" (like VL-1, SK-1 etc.) are usually good ones (except perhaps PT-1) and particularly those ending on "Z-1" are great. Apparently all old Casio instruments (before CTK- series) with an "8" in their type number had a ROM-Pack slot and key lighting. The only known exception is the keyboard CT-8000, which was part of the ultra-rare modular stage organ Symphonytron 8000.

I have done this! ROM-Pack hack In my 2nd EP-20 specimen I removed the music rom with an SMD hot air soldering station to transplant the 'World Songs' rom from a RO-551 and vice versa and though play the Muppets music on other keyboards. Only regard that the "World Songs" cartridge exists with 2 different IC shapes (square or rectangular). Important is to use a ROM-Pack with square 44 pin IC "OKI MS5268". I used a RO-551 with JASRAC label and rough flat back (Japanese version?, apparently came with my PT-80). Other RO-551 (no JASRAC, shiny back with 3 holes) contain a rectangular 22 pin IC "Matsushita MN6404xxxx" that won't fit. Theoretically to the EP-20 also a ROM-Pack slot can be added, but this would be mechanically very difficult and not worth the effort. Another special ROM-pack is inside SK-5 (SK-8 hardware), but it likely needs a non-standard sound set that does not correspond to SK-8 or others.

The upper 4 preset sound numbers are user presets in RAM. If I remember well, they only contain the named contents after a reset (see user manual), else it there may be random mess or silence on 96, 97, 98, 99.

I own a Casio CT-6000 and service manual, but haven't analyzed its complex hardware further (beside making PCB photos and contact cleaning). It employs 3 main voice sound ICs "NEC D932G" (64 pin zigzag) and the unique blip percussion IC "Hitachi HD61701" (54 pin SMD), everything controlled by the CPU "NEC 7811G-081". Although this keyboard was the flagship of 1984, it has nothing to do with phase distortion. The D932G appears to be a velocity sensitive successor of the famous "NEC D931G" (42 pin DIL, found in MT-65 and such). Beside CT-6000 it was only used in the early Casio e-piano CPS-101 (and possibly other CPS-series). It communicates with the CPU through 8 input and 4 output pins, has 17 bit audio and additional 14 control output pins for external filters, mixing ratio, stereo chorus and the like. The velocity sensitive highend midi keyboard contains 3 of these unique sound ICs; each is wired to an own DAC with different fixed analogue filter (each 3 control lines). The outputs are mixed; in chord mode the 3rd sound IC is used for chord only, else all 3 are layered as main voice. I suspect that in classic Consonant-Vowel manner the mixing ratio between multiple differently filtered sound ICs changes with keyboard velocity. The existence of so many switchable filters seems to disprove the rumour that CT-6000 was a secret unofficial first phase distortion instrument. The high timbre quality rather results of 17 bit DAC resolution and complex analogue post-processing through filters and a costly 3 line BBD stereo chorus. (Interesting is that US patent 4387619 poorly describes a consonant-vowel hardware that implements a so-called "staggered multi-performance mode", i.e. a preset sound can consist of multiple layered subvoices occupying 2 or 4 polyphony channels ("duet", "quartet" - a feature that was not released until the much later "unison" modes in the CPU controlled Casio CT-6000), which needs independent management of key presses and polyphony channels. In the described self-contained LSI chip without CPU control the routing was quite a mess.) The HD61701 produces 24 lofi percussion sounds through 4 audio outs those are routed through external discrete filters to shape timbres.

Regarding old hardware and ESD. I remember that Commodore C64 computers in shopping centers indeed often died by it. There were atrocious synthetic rugs (and escalator handrails) where I got jolts when ever I touched metal in winter. When we kids had loaded a C64 game from cassette (secretly "lended" from a shelf nearby) and plugged a joystick in, often the thing crashed and needed to reload everything (which could take 15 to 30 minutes!). Even worse, sometimes accidentally touching the joystick port pins caused a shock that killed the port IC and so made one joystick direction and some keys stop working. Also the userport at the back was sensitive. One reason for ESD damage is hotplugging ungrounded CRT TV sets or monitors. When they switch on, the CRT (acting as a glass capacitor) is charged to about 28KV with the chassis GND as its 2nd pole. If the TV is grounded (through mains or antenna plug) the 2nd pole stays at earth level, but if not, the entire chassis GND will instead charge to half of that highvoltage. If now the TV is plugged into anything grounded (e.g. antenna jack of a computer, game console or audio-in of an amplifier) that charge can flow into the connected device, and if something else than a GND pin connects first, it may fry ICs. This was likely the main reason for the warnings never to hotplug SCART cables. Among VHS recorders I did this all days without any damage (beside lousy plugs falling apart). Some think the warning was due to the 12V at some pins that might flow wrongways, but it is certainly an ungrounded CRT TV chassis that can cause mayhem.