CT 701

[Bondo2]

Hi,

 I have a CasioTone 701 keyboard, the only part of the keyboard that works is the Casio Chord side when the switch is on Chord or fingered, if it is off then nothing works at all. Any ideas ?, do you know where I can get the service manual ?

[IanB]

I can't find a service manual either. I really wish Casio would release all these antique service manuals so the legacy can be kept alive.

 

In the meantime I'd open her up and look for bad connections, particularly to the keyboard section, and check all the boards have all their power rails. Check that any switches are working in all positions. If you want to post some images and "brainstorm" this on the forum, I for one will be happy to participate. It may be we can find the fault as a group effort. Do you have any test gear?

[Chas]

I'd experiment with the switches on the left that engage the accompaniment and Casio Chord features. Turn everything to 'off', as parts of the keyboard are disengaged from the main selected voice when accompaniment features are activated. 

 

Do the drums work at all? Can you tell us which  of the 701's features do work? Once we know what parts are functioning, that might help narrow down potential faults.

 

One thing that did cross my mind is that the 701 has a feature where it uses a light pen to scan music encoded as bar codes that it can then play back via a sequencer. Ensure that the keyboard isn't stuck in the scan mode and is waiting to receive data via a light pen, or that it's not stuck in some scanned music play mode. There are a number of videos on YouTube showing how this feature is used. 

 

Lastly, I hope you do get it all working. The CT701, along with the MT70 and CT1000P are unique in using Sine Wave synthesis. Casio only used this for about 3 years before dropping it and then stuck with Consonant Vowel synthesis until PD/ PCM/ sampling technologies took over. Sine Wave synthesis has a unique timbre and is very well suited for organ and flute sounds. Check some YouTube videos to hear how interesting sine wave synthesis can sound, especially through effects units.

 

 

 

[Bondo2]

1 hour ago, IanB said:

I can't find a service manual either. I really wish Casio would release all these antique service manuals so the legacy can be kept alive.

 

In the meantime I'd open her up and look for bad connections, particularly to the keyboard section, and check all the boards have all their power rails. Check that any switches are working in all positions. If you want to post some images and "brainstorm" this on the forum, I for one will be happy to participate. It may be we can find the fault as a group effort. Do you have any test gear?

I will open it up and see,  unfortunately I don't have any test gear as my digital meter died.

[Bondo2]

55 minutes ago, Chas said:

I'd experiment with the switches on the left that engage the accompaniment and Casio Chord features. Turn everything to 'off', as parts of the keyboard are disengaged from the main selected voice when accompaniment features are activated. 

 

Do the drums work at all? Can you tell us which  of the 701's features do work? Once we know what parts are functioning, that might help narrow down potential faults.

 

One thing that did cross my mind is that the 701 has a feature where it uses a light pen to scan music encoded as bar codes that it can then play back via a sequencer. Ensure that the keyboard isn't stuck in the scan mode and is waiting to receive data via a light pen, or that it's not stuck in some scanned music play mode. There are a number of videos on YouTube showing how this feature is used. 

 

Lastly, I hope you do get it all working. The CT701, along with the MT70 and CT1000P are unique in using Sine Wave synthesis. Casio only used this for about 3 years before dropping it and then stuck with Consonant Vowel synthesis until PD/ PCM/ sampling technologies took over. Sine Wave synthesis has a unique timbre and is very well suited for organ and flute sounds. Check some YouTube videos to hear how interesting sine wave synthesis can sound, especially through effects units.

 

 

 

I turned all the switches off and this is when none of the keyboard keys produces any sound. 

I don't have the light pen

[Chas]

3 hours ago, Bondo2 said:

I turned all the switches off and this is when none of the keyboard keys produces any sound. 

I don't have the light pen

 

 

Have a look at this video and see if the switches Paolo pushes at around the 11.00 mark are on or off on your CT701. That's how to activate the light pen features. Worth a look just in case yours are still in the scan position, which might explain the keyboard not producing any sound:
 

 

[Bondo2]

7 hours ago, IanB said:

I can't find a service manual either. I really wish Casio would release all these antique service manuals so the legacy can be kept alive.

 

In the meantime I'd open her up and look for bad connections, particularly to the keyboard section, and check all the boards have all their power rails. Check that any switches are working in all positions. If you want to post some images and "brainstorm" this on the forum, I for one will be happy to participate. It may be we can find the fault as a group effort. Do you have any test gear?

Just checked, it's not in scan mode and I found something interesting,  the keys are not disconnected or faulty because in memory recording mode the leds on top of the keys light up if I press them even though there is no sound

[Chas]

Without a service manual, and more detailed information or a video showing exactly how the 701 is behaving (or not), it's hard to pin point where the problem(s) may lie.

 

I'd double check the "memory" section (see pic below) to absolutely ensure that it's not in a step sequence record mode or that it's waiting for data from somewhere. 

 

 

Also check the "balance" control knob (see below pic). This adjusts the relative volume levels between melody and accompaniment. If it's rotated all the way over to the "accomp' side, it will mute the main voice (melody).  If it's rotated all the way to the "melody" side, it will mute the accompaniment. It's possible that it is faulty and is permanently muting the melody, which would explain why you aren't getting any melody tones sounding. Try wiggling it back and forwards while attemptinging to play a melody tone. See if there are any crackles/ signs of life indicating a faulty potentiometer.

 

[Chas]

17 hours ago, Bondo2 said:

Just checked, it's not in scan mode and I found something interesting,  the keys are not disconnected or faulty because in memory recording mode the leds on top of the keys light up if I press them even though there is no sound

 

I've managed to find a PDF of the user manual (see attachment).

 

As you said, the LEDs are lighting up in this mode indicating that the keyboard and keyboard scanning matrix are functioning correctly. Also, if the LEDs are lighting when you play the keyboard, this shows that it is not in normal play mode. Have a good look though the manual as switches need to be in a specific order for certain functions and modes to operate. Page 11 shows how to set the keyboard to play a preset tone.

Pages 48 and 49 show trouble shooting charts for possible causes of no melody tone.

Also, check out page 10. The 701 uses a battery backed up memory with three AA batteries installed on the underside of the keyboard. As with many keyboards, if the batteries fail or are flat, it can scramble the contents of the memory causing all sorts of non functioning issues. Ensure fresh batteries are installed and that there are no signs of leakage and/ or corroded/ oxidised connectors.

The owners manual can be downloaded via the attached file below.

 

 

Casio_Casiotone_701_Manual.pdf

[Chas]

And if all else fails and you're feeling brave, I also managed to find the 701/ 601 service manual. Any good electronics technician/ synth repairer should be able to use this to diagnose and repair any potential faults if they exist with yours.

 

 

 

701 601 Casiotone_Textbook_701_601.pdf

[IanB]

Chas, you deserve a prize for finding the manual, where did you find it?! I'm just poring over it now.

 

Bondo2, do the drums work? This is a useful diagnostic to know.

[Bondo2]

1 minute ago, IanB said:

Chas, you deserve a prize for finding the manual, where did you find it?! I'm just poring over it now.

 

Bondo2, do the drums work? This is a useful diagnostic to know.

What do you mean by drums?, you mean the sound effects on the left?

[IanB]

There's a rhythm section.

[Bondo2]

9 minutes ago, IanB said:

There's a rhythm section.

Yes they work, everything works except the right side of the keyboard (none casio chord) when casio chord is on, and none of the keyboard when it's off 

[IanB]

Okay, so that narrows it down. We know the processor's working and we know the output mixer's working and we know one of the Music LSI's is working. Once you've done everything Chas has suggested it'll be a case of opening it up, and unless you're very lucky to find something obvious e.g. disconnected cable, you would need at least a multimeter.

[Bondo2]

56 minutes ago, IanB said:

Okay, so that narrows it down. We know the processor's working and we know the output mixer's working and we know one of the Music LSI's is working. Once you've done everything Chas has suggested it'll be a case of opening it up, and unless you're very lucky to find something obvious e.g. disconnected cable, you would need at least a multimeter.

Tried the troubleshooting, didn't make a difference 

Here is a video

 

[Chas]

53 minutes ago, Bondo2 said:

Tried the troubleshooting, didn't make a difference 

Here is a video

 

 

Look at the two red arrows in this screen shot.

The first arrow on the left - you are in "Accomp Tone Set" mode. The keyboard is expecting you to select an accompaniment tone. Switch this to 'off'.

The second arrow on the right, the "balance" control rotary knob. As mentioned in my earlier post, this sets the relative volume between accompaniment and melody. Yours is set all the way to accompaniment, which will silence the 'melody' tones. Have you not tried turning this like I suggested in my previous post? Turn it to the center (12 o'clock)  position, or all the way to point at "melody".

Then see if you are getting melody tones on the rest of the keyboard.

Also, please download and read the PDF owners/ operation manual I attached above. The 701 has numerous modes that you have to correctly select with the switches and controls, all the details of how to select these are in the manual.

 

[Chas]

2 hours ago, IanB said:

Chas, you deserve a prize for finding the manual, where did you find it?! I'm just poring over it now.

 

Bondo2, do the drums work? This is a useful diagnostic to know.

 

I just did a Google search for "CT701 user manual", then found them as a download link in a keyboard forum - I forget which!

[IanB]

Ah, I was searching for Service Manual. Note to self: be less specific

 

And I'm also slightly irritated at myself that I didn't notice he's got the balance set to Accompaniment.

[Bondo2]

11 hours ago, Chas said:

 

I just did a Google search for "CT701 user manual", then found them as a download link in a keyboard forum - I forget which!

 

11 hours ago, Chas said:

 

Look at the two red arrows in this screen shot.

The first arrow on the left - you are in "Accomp Tone Set" mode. The keyboard is expecting you to select an accompaniment tone. Switch this to 'off'.

The second arrow on the right, the "balance" control rotary knob. As mentioned in my earlier post, this sets the relative volume between accompaniment and melody. Yours is set all the way to accompaniment, which will silence the 'melody' tones. Have you not tried turning this like I suggested in my previous post? Turn it to the center (12 o'clock)  position, or all the way to point at "melody".

Then see if you are getting melody tones on the rest of the keyboard.

Also, please download and read the PDF owners/ operation manual I attached above. The 701 has numerous modes that you have to correctly select with the switches and controls, all the details of how to select these are in the manual.

 

The switch cap is not mounted correctly so while it shows as if it is turned all the way counterclockwise, it is not. If I turn it all the way to melody then even the casio chord side doesn't produce any sound (the sound is louder when turned to accompaniment)

As for the switch, on or off makes no difference. I read all the troubleshooting and modes already

[Chas]

5 hours ago, Bondo2 said:

 

The switch cap is not mounted correctly so while it shows as if it is turned all the way counterclockwise, it is not. If I turn it all the way to melody then even the casio chord side doesn't produce any sound (the sound is louder when turned to accompaniment)

As for the switch, on or off makes no difference. I read all the troubleshooting and modes already

 

It's very hard to diagnose issues for a keyboard only from limited information, descriptions, and a 22 second video. Whenever something has multiple modes and is experiencing problems, the first thing to do is to initialize everything back to a default state. Thus I watched your video and saw two settings that weren't in the default state and highlighted these as potential culprits. We can only go by the information that you give to us. I don't have a CT701 to check against and can only read the PDF manual and go by what you tell/ show us to try and determine the cause of your 701's issues. 

With regards to "The switch cap is not mounted correctly", this is the type of information we need to have known before attempting diagnosis. The caps are normally a push fit onto the shafts, and some caps only fit on in one position if it is a D shaft (compared with a splined shaft) -  I don't know what the 701 uses. My CT403 (1983) has a splined shaft for the balance control, whereas my CT201 (1980) has a D shaft for the volume. The CT701 is from 1981, so it might use either type of shaft. The question has to be asked, why is yours not on the shaft in the correct position? When/ how did this happen? Is there something wrong with this control? The control is most probably a dual potentiometer, one for the accompaniment volume, the other for the melody volume. They are often stacked together and operate from one shaft, with each potentiometer working in the opposite way to the other i.e. rotating will cut one pot and increase the other.

As you have found, this control affects the volume balance between the accompaniment and the melody tone. When moved all the way to the melody side, it cuts off the accompaniment. When moved all the way to the accompaniment side, it cuts off the melody. If there is a fault with the melody potentiometer, this could be why there is no melody sound playing. The fact that this control cap is not showing the correct position could indicate that it has previously been forced/ damaged or messed with. With everything else seemingly OK, this to me is the most likely culprit right now. To confirm or eliminate this as the cause, the keyboard needs to be opened up and this control inspected and tested before any further tests are carried out.  

[IanB]

@Chas The manual you found doesn't unfortunately contain a complete circuit diagram and PCB layouts, but instead only some parts of the circuit as isolated circuits. The block diagram seems to indicate the Balance control is a dual pot (which would probably be log-antilog profile) but it might actually be a single pot configured as a panpot. We would need to see inside to know which. If @Bondo2 is satisfied that he has tried all the settings as suggested, the next stage would be to open it up. Beyond a visual inspection, at least a multimeter would be required for basic fault finding.

 

However from the manual we can see this is actually a digital sound source through Digital To Analogue Converters (quite surprising for its day) and is rather complex internally- it actually uses 4 bit DACs then scales them using sample and hold circuits and there are many things that could be wrong with that which would require an experienced engineer with proper test gear.

 

There's no harm in a look inside though. It may be something fairly straightforward.

[Chas]

@IanB - absolutely agree with you. And yes, it's a shame that the service manual lacks full circuit diagrams, though it does appear to show a dedicated test sequence for fault finding the main sections.

 

My electronics knowledge is very basic, but as I've always been taught, check the obvious and most basic items first. Many times a problem turns out to be something as simple as a loose wire or cracked solder joint. A close visual inspection can often reveal a fault very quickly, and as a unit has to be taken apart for testing anyway, a visual inspection of the obvious is the first thing I would do to see if anything is obviously amiss.

 

I'd also add that in my experience of this era of Casios, they are in general very, very well built and very rarely suffer major failures. Crackling pots and intermittent switches are often the only things that have ever given me issues, along with dried out film capacitors (my CT403 produced a spectacular amount of smoke when its teeny tiny capacitor went pop!) I've never experienced failure of a CPU or LSI chip in the many old Casios that I own, though that's not to say that they won't ever fail.

 

As just about everything else in this misbehaving 701 appears to work, and it is actually generating sound, that wonky balance control is what I would hone in on first. It's visually out of place, and in operation it has the ability to cut the sound to the main keyboard voice, making it a potential suspect. Of course, Casio sometimes use two separate sound generating chips for an accompaniment and a main tone, so it is still possible for a sound chip failure to be the issue.

 

Take it apart and have a look is what I suggest, and using a simple multimeter will quickly ascertain whether the balance potentiometer(s) are working correct or not. If it's been forced, it might also be visually obvious when viewing from the inside.

 

 

[Chas]

21 hours ago, IanB said:

@Chas

However from the manual we can see this is actually a digital sound source through Digital To Analogue Converters (quite surprising for its day) and is rather complex internally- it actually uses 4 bit DACs then scales them using sample and hold circuits and there are many things that could be wrong with that which would require an experienced engineer with proper test gear.

 

Also as you pointed out, for a home keyboard produced in 1981, the CT701 is surprisingly advanced and appears to be using a form of digital synthesis. @CYBERYOGI =CO=Windler has done a lot of research into the workings of old Casios and IIRC, found that a small group of Casios (CT701, 601, CT1000P and MT70) use a form of sine wave synthesis utilizing digitally generated sine waves. Most other Casios from the first half of the 80s used Consonant Vowel synthesis for sound generation.

 

Interestingly, though Casio dropped sine wave synthesis in their home keyboards around 1983, it appears that Phase Distortion synthesis (introduced late 1984) starts out with a basic sine wave, and then uses PD to distort the wave to generate new waveform shapes. Maybe these early sine wave Casio home keyboards were actually a very early implementation of what would go on to be developed into Phase Distortion? I wonder! 🤔

 

 

[IanB]

@Chas Indeed. I haven't done a "thorough analysis" but it has a microcontroller running DACs to produce sine waves as you say. It's very advanced for its time. Even more interesting, it then follows the DAC with an expansion circuit to extend the range, using 3 CPU controlled settings to turn 4 bits into 12. It sort of runs through the 4 bits, then turns up the "volume" and does it again, then turns up the "volume" and does it again, which is very much a precursor to the CZ synths which use a similar system to extend the range of the DACs in them. I agree there's some strong family resemblance here!

 

It's also interesting to me at least that Casios tend to have impressive power supply circuits with multiple stages of activation to prevent pouring current into short circuits, etc, rather complex for their time. If you remember that keyboard we all had a hand in cyber-repairing a few months ago, it was one of the logic gates in that which had failed. I have a great deal of respect for the engineers of that era in terms of both electronics and mechanical systems (old cassette decks, record players, VCRs, etc were often mechanical masterpieces). You can see how thoroughly they considered their designs when you look at the diagrams, boards, etc.

 

Back to the 701, it's an impressive piece of design for its era. Digital sine waves, crikey! This has made me want to get my hands on one!