CT 701

[pianokeyjoe]

Woooow!! Thankyou my friend! For the information! @CYBERYOGI =CO=Windler! Ok, so essentially I would need 2 UMR2 midi retrofit boards in the MT45 due to basically it being 2 keyboards in one.. Kinda like home organs. Or I midi up only the MT11 section of it. Though, I do have an MT11 keyboard too, I rathered Midi up the MT45 as I own 2 of those and can afford to tinker with one of them. I only have ONE MT11 so it is rare and costly at $141 all the way from Australia.

[karuta]

I have a 501 with the same problem, it only plays 4 notes at a time, the funniest thing is that if you keep hitting the same key several times, one time it plays, another time it doesn't... the only way to make chords with 4 notes, and leave it with accompaniment, which is muted, then on the right side you can make the 4-note chords. (the battery works normally at this point)

A 701 appeared, is it worth buying even with the 501? is it the same sound? I notice that my 501 has a digital display and the 701 has nothing... it just seems to have buttons on the chassis.

greetings from Brazil.

 

OBS AO NETO (EM PORTUGUES JÁ QUE ELE É DO BRASIL)

O meu quando liguei a primeira vez queimou o mesmo capacitor, foi uma fumaçeira pra tudo que é lado

[Chas]

5 hours ago, karuta said:

I have a 501 with the same problem, it only plays 4 notes at a time, the funniest thing is that if you keep hitting the same key several times, one time it plays, another time it doesn't... the only way to make chords with 4 notes, and leave it with accompaniment, which is muted, then on the right side you can make the 4-note chords. (the battery works normally at this point)

A 701 appeared, is it worth buying even with the 501? is it the same sound? I notice that my 501 has a digital display and the 701 has nothing... it just seems to have buttons on the chassis.

greetings from Brazil.

 

OBS AO NETO (EM PORTUGUES JÁ QUE ELE É DO BRASIL)

O meu quando liguei a primeira vez queimou o mesmo capacitor, foi uma fumaçeira pra tudo que é lado

 

From what I have read, the CT501, 601, 701, CT1000P and MT70 are all based on the same "Sine Wave" sound engine that is unique to these models. The CT501 is the full sized version of the MT70 and IIRC correctly, has an identical feature set. The earlier 701 and 601 are essentially the same keyboard, with the 601 being a lower spec model by losing the barcode scanner pen and related features. The CT1000P is a "semi programmable" additive synth using the same sine wave synthesis engine along with additional features (programmable arpeggiator/ sequencer for instance), but otherwise has nothing else in common with the 501, 601, 701 and MT70.

Also note that the 701 has a three character LED display that is related to the barcode and memory feature. As the 601 does not include that feature, it has no LED display.

 

From what I understand, the 701 *should* have the same basic sound as the 501, plus you get an extra octave of keys and the two "sound effects" buttons. However, Casio have been known to tweak hardware even in the same series of models so I can't 100% guarantee that they sound 100% identical. Check out some YouTube videos that will give you a good idea of how close they are sonically. 

Edited January 15, 2022 by Chas

[karuta]

11 hours ago, Chas said:

 

Pelo que li, o CT501, 601, 701, CT1000P e MT70 são todos baseados no mesmo mecanismo de som "Sine Wave" exclusivo desses modelos. O CT501 é a versão em tamanho real do MT70 e do IIRC corretamente, possui um conjunto de recursos idêntico. Os 701 e 601 anteriores são essencialmente o mesmo teclado, com o 601 sendo um modelo de especificação inferior, perdendo a caneta do scanner de código de barras e recursos relacionados. O CT1000P é um sintetizador aditivo "semi programável" usando o mesmo mecanismo de síntese de onda senoidal junto com recursos adicionais (arpejador/sequenciador programável, por exemplo), mas não tem mais nada em comum com o 501, 601, 701 e MT70.

Observe também que o 701 possui um display LED de três caracteres relacionado ao código de barras e ao recurso de memória. Como o 601 não inclui esse recurso, ele não possui display de LED.

 

Pelo que entendi, o 701 *deve* ter o mesmo som básico que o 501, além de obter uma oitava extra de teclas e os dois botões de "efeitos sonoros". No entanto, a Casio é conhecida por ajustar o hardware mesmo na mesma série de modelos, então não posso garantir 100% que eles soem 100% idênticos. Confira alguns vídeos do YouTube que lhe darão uma boa ideia de quão próximos eles estão sonoramente. 

Thanks for the quick response. I was in doubt since a 701 appeared for sale, I thought it was older, without the "digital" part. I also have an MT-68 in my collection. About the problem of working it partially, I want to post a video for you to understand soon.

[CYBERYOGI =CO=Windler]

The MT-70 has only 2 indentical sinewave soundchips (may be Casiotone 501 too), while Casiotone 701 has 3 (i.e. 12 instead of 8 note polyphony). Also my Casio AT-40 contains 2 of these.

 

If only every n-th note is audible, likely one of the soundchips is dead or a pin disconnected. Their digital audio is daisychained from chip to chip instead of using separate DACs, which may complicate fault search.

Edited January 16, 2022 by CYBERYOGI =CO=Windler

[karuta]

tks again, video showing the problem: (SORRY THE DOG) 😅

 

 

 

Edited January 16, 2022 by karuta

[pianokeyjoe]

oh mee oh my. Yes I have never seen that before but seems indeed the 2 sound chips ARE multiplexed. Since there is NO sound output for the accord section when ON, that leads me to believe the IC responsible for the Casio Chord is either cut off from the sound output(check the sound output of THAT IC!!), or there may be an issue with the 7400 ic chip that multiplexes the synth out of both chips.. but then why would the melody sound at all and why no strange over glitching of the keyboard if indeed the sound gen is bad or the multiplexer is bad? I am really really leaning towards the audio path beyond the sound gen ic. Namely an OP AMP!! Yey! What a surprise lol! From what I remember from tech school those op amps of old, were notorious for going bad even from factory sometimes. Very sensitive to static electricity. Think about it, the keyboard is still working and is not glitching like there is dead microprocessor or other major important thing wrong. Just no audio from the accord section which ties to the "second" voice of the 8 voice polyphony of the keyboard.. Nice trick they did back then. Check your audio path.

[IanB]

So, eerily similar to the CT6500 thread with its "1Hz timesharing", i.e. the CPU assigns notes to Music IC A for one second (or so) then assigns to Music IC B for one second, back and forth. If each is handling a maximum of 4 notes polyphony, holding down 4 keys and then pressing another forces it to assign to the other IC, which is the one with no output.

 

So yes, either one chip is dead, or its support circuitry is faulty somewhere, or something is dead in its audio path before the two chips' outputs are mixed...

[CYBERYOGI =CO=Windler]

AFAIK the analogue sound output is NOT multiplexed at all, but one sound chip feeds its digital audio into the next one, so they get digitally summed and finally output by the last soundchip in that chain through a single resistor ladder DAC.

 

Analogue multiplexing with demux after DAC existed in other hardware families of that time (and Bontempi even did it for stereo), but not the sinewave hardware.

Edited January 18, 2022 by CYBERYOGI =CO=Windler

[Thumb]

Nice thread, I have a 701 with similar problem, it plays only note every 5th or 8th time I hit the keys and drop an octav on the third time !!? So I guess one of the chips are broken too   Everything else works fine , and I can not believe the fault should be the CPU , the keyboard input is fine  to !!

 

Any one have a HD43517 IC they would like to sell ?

[pianokeyjoe]

Hmm.. how are these IC chips going bad without circuit bending? I have my 701 that so far(fingers crossed)works but look very ugly and has a broken key but other than that it is working. I am starting to suspect the failures are due originally to some discreet components or power supply rail issue causing an upswing in +vcc on those chips to cause them to fail like that.. I do have several Casio models with built in AC power mains supply in them, and this is starting to worry me..

[IanB]

@pianokeyjoeOn the other hand, these chips are just very old and all chips eventually fail with enough time.

[Thumb]

I do not know, but I do repair of alot vintage gear and yes chips can fail. But first I had to change the cable from the keybed the metal on the flex cable was crack /missing given the tone failing out and I did a re-cap on the main board and THEN after that I got this "New" problem !!! And it puzzle me if i have do something wrong but all looks good and after the help from @CYBERYOGI  schematic I narrow it down to be the LSI chips ,somehow

[IanB]

Have you checked all the power supplies at the chips themselves? Ideally I'd get an oscilloscope on them to see what is happening. The recap may have introduced a problem.

[Chas]

"Bit Rot" is an unfortunately not an uncommon occurrence, often happening as a result of old age and/ or voltage spikes. Some chips are notorious for this, for instance some of the custom chips in the Commodore 64 computer are well known to fail causing all sorts of issues. IIRC, the SID sound chip and also the PLA chip used for the display can often go bad. Luckily some chips are being reproduced or even emulated via FPGA means, though some custom chip firmware is still under copyright causing legal issues.

 

Another example is the chip (actually a resistor pack) used as part of the tachometer circuit in many 1980s GM vehicles. One of the resistors inside the chip goes bad with age (all the others continue to work fine) leading to an over reading or non functioning tachometer. My own 86 Monte Carlo has this issue, and luckily it can be rectified by cutting the legs of the chip where the bad resistor connects, and soldering in place a conventional resistor of the correct value. It's not pretty but it's hidden away from sight and solves the issue.

 

More of a concern are modern devices where it's impossible to read the LSI chips without proprietary software readers. That and the fact that many are so complex, it would be a massive task to read and reproduce the firmware used on them, plus the nightmare of trying to physically swap out a modern SMD LSI chip. Even some of my early 80s Casios use tiny SMD LSIs that are beyond my ability, to swap out though luckily Casios generally tend to be very reliable. I've only ever had two failures - a RIFA Capacitor (aka RIFA Bombs) in my CT403 self destructed in a most spectacular fashion (I never knew so much smoke can come from such a tiny component), and one of my HT6000s went dead on me while playing it. The CT403 was easy to sort by replacing the RIFA Capacitor with a better quality replacement and it was up and running again. My HT6000 though was not so easy. I took it apart to see if anything was obvious but my electronics skills are rather rudimentary and I couldn't spot anything obviously amiss. I found that the power board had voltage and appeared to be sending it to the main board, but that was as far as my skills go. As I have two other HT6000s that work I put the dead 6000 back together to be sorted at a time when I have the required skills and knowledge. 

Edited June 9, 2022 by Chas

[CYBERYOGI =CO=Windler]

With really ancient chips (20+ years old) don't fear of firmware (c)-trolls. Its the human right of culture preservation. Companies anyway rarely care about things those are >6 years out of sale (unless they make a living on a monopoly of specifically repairing those, or they were stupid enough to use the same encryption key inside everything modern). The greater problem is to figure out how the chip actually works. Particularly when old ones include analogue components or use odd voltages (Yamaha has -9V key matrix signals) replacement would be complicated even when decapped to decipher the dieshot and code that into an FPGA.

 

AFAIK old Casio sound chips use a single sound generator circuit for all polyphony channels and only swap the register contents (selected waveform + envelope and current position within + note pitch) by a rapid hardware multitasking because every memory cell is a shiftregister with the depth of the polyphony (e.g. 4 cells for 4 notes) stepped with the system clock. So strange behaviour may mean that one memory cell is dead and produces garbage, and if inside a shift register, shifting it will make all other cells contain the same garbage that e.g. makes it skip notes. If always the same n-th note is dead, then it likely is not a shift register but normal memory that will not shift the fault into the next cell.

[Thumb]

So the CPU "calls" and tell the HD43517 chip which has the "sounds" has to be, and each 43517 has 4 notes ! It is not the CPU who does  the sounds. Like with normal CPU /DAC setup where it is all software !?

The damm thing is that it worked before I change the keybed ribbon cabel 😥 That make me think that something eles is wrong than the chip(s)

[pianokeyjoe]

32 minutes ago, Thumb said:

So the CPU "calls" and tell the HD43517 chip which has the "sounds" has to be, and each 43517 has 4 notes ! It is not the CPU who does  the sounds. Like with normal CPU /DAC setup where it is all software !?

The damm thing is that it worked before I change the keybed ribbon cabel 😥 That make me think that something eles is wrong than the chip(s)

I must have missed that little detail in all the discussion, but I do not doubt my failing eyes would have missed it.. You say you changed the ribbon cable to the keybed and THEN the issues started? Hmm, check the ribbon cable for continuity for each of the strands(should be about 14 to 16 strands). Best way to check is with a digital multi meter with the sound setting(or with the -->I--  symbol setting. IF you should NOT hear sound when you test each end of the ribbon cable strands, then bad cable. Next if you DO hear sound and cable is good, is check the solder points for both the keybed and the main board were you soldered. Though I suspect this older board used the ribbon cable PLUG on the mainboard and soldered on ribbon cable on the keyboard contact board? IF so, then unplug the ribbon and check the inside of the plug socket on the mainboard for dust and the ribbon for dust or obstructions.

 

Now I reread the post more clearly.. Sorry. You changed the cable FIRST, then you recapped the keyboard and has new issue? Check that ribbon again. WHAT is the NEW PROBLEM? That would be very helpful to know in order to further assist..

Edited June 9, 2022 by pianokeyjoe
more to say

[Thumb]

re-Cable is fine I have full respond via keyb. bus system , also I can see the LED flashing at key press and the the problem are on all keys. The fault is it plays notes every 5 or 7th time, it I can get four notes playing after pressing the keys in sequence. 

I have have check both "analog out" and they have signal out so it is not after HD43517.

it is like it is "counting" and only plays some of notes at this patten 5 or 7/8,  in "fingered" mode it jumps tone in octaves !

[IanB]

Ah, so it's likely the DAC multiplexer that's faulty then...

[IanB]

The Casiotone 701/601 textbook shows two Music LSIs, two DACs and analogue mixing of the signals (also with the percussion source) so it should be possible to trace the audio on the circuit board to see if one or both DACs are outputting sound. The mixer will presumably be a simple op amp virtual ground mixer, probably inverting.

 

A simple audio probe, that is just a wire connected to the input of an amplifier (highest impedance you have) should be sufficient to do that.

Casio_Casiotone_CT-701 601 Casiotone_Textbook_701_601.pdf

[Thumb]

Well I have checked D/A out and after both opamp I can get a signal , by the way this one has only one AM6012 at the second 43517 and at the first 43517 there is a resistor adder so what puzzle me how can it skip some key presses but still play the right notes , there must be something counting . So the 701 plays all tones but only at a sudden patten every 5th or 7th or I can trig 4 notes at a time , the max notes I can get is four

[CYBERYOGI =CO=Windler]

The sound IC is not a DAC by itself but outputs waveforms (4 polyphony channels, each made from 5 summed sines with volume envelope) through a DAC. With chord mode off, all 3 sound ICs daisychain digital audio through a single DAC. Only in chord mode the 2nd DAC is used to route the chord/accompaniment through different analogue circuitry. See here:

 

https://www.casiomusicforums.com/index.php?/topic/21355-mt-70-analysis-and-hopeful-repair/#comment-79036

 

Edited June 15, 2022 by CYBERYOGI =CO=Windler

[Thumb]

Well, that kind of smart. So  I think I got a bad chip (HD) I will try swap them to see if it change things, I come back.

[giano]

I went to an art exhibition in Munich this week which included a live music performance.

 

The musician entered the room with a padded bag and guess what was in there? the good old CT-701 in all its glory