Yamaha CS-50 All Keys of E not working

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Yamaha CS-50 All Keys of E not working

Postby wizardmix » Tue Jul 04, 2017 8:00 am

Hey all, new to the forum posting this question on behalf of a friend but I am a synth head myself so I'll be back with my own problems I'm sure :D

My friend just acquired a CS-50 where (oddly) all of the E keys are not working, which seems unusual. That seems to be the only problem. This CS-50 has been sitting unused for over a decade. Not knowing the circuitry of a CS-50, I thought I might ask the question here and see if anyone might know what that's about? (or) If they've encountered a similar problem, what the fix might involve?

Since it's all of the E keys and only the E keys, it seems like it would have to be the way the circuitry is mapped as opposed to broken keys but I leave it in the capable hands of the experts here. Thanks in advance!
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Re: Yamaha CS-50 All Keys of E not working

Postby madtheory » Tue Jul 04, 2017 10:01 am

I'm guessing you've never used a service manual before? If so, take it to a tech. This is not a simple fix.
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Re: Yamaha CS-50 All Keys of E not working

Postby gcoudert » Tue Jul 04, 2017 2:22 pm

Or play in E flat major / C minor...
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Re: Yamaha CS-50 All Keys of E not working

Postby wizardmix » Tue Jul 04, 2017 8:26 pm

madtheory wrote:I'm guessing you've never used a service manual before? If so, take it to a tech. This is not a simple fix.


Wow m8, thanks for the help and taking the time to post that deduction, you really do earn your credentials on here. I personally never would have thought to do either of those things!! Asshat.

Anyone else who would like to help?
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Re: Yamaha CS-50 All Keys of E not working

Postby Mooger5 » Tue Jul 04, 2017 11:45 pm

First off, good luck with that temperament. That reply you did´t like to read is actually a sensible one. The CS synths of that vintage are notorious for their complicated innards and the service manuals are laconic.

NOW where you say "Since it's all of the E keys and only the E keys, it seems like it would have to be the way the circuitry is mapped as opposed to broken keys" your reasoning seems right. So why not have at least, a non-invasive try.

Looking at the schematic, there´s like only one path responsible for all the E keys going from the keyboard to the Keyboard Assigner Circuit. The offending part might be a broken wire/cold solder joint.
Lift the keyboard and look for a green shielded wire going to the KAS board underneath. The central conductor is what carries the note information. According to the manual there´s also a "grass green" wire around; it´s not that one. If it helps, the green wire you´ll be looking for should have a blue wire next to it, or they´re both arranged in a twisted pair or something.
You´ll then have to test that path for continuity.

That´s my best and only shot. Beyond here you better find an experienced tech. The CS50 is a very valuable synth and might be worth the expense.
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Re: Yamaha CS-50 All Keys of E not working

Postby wizardmix » Wed Jul 05, 2017 1:54 am

Mooger5 wrote:First off, good luck with that temperament. That reply you did´t like to read is actually a sensible one. The CS synths of that vintage are notorious for their complicated innards and the service manuals are laconic.

NOW where you say "Since it's all of the E keys and only the E keys, it seems like it would have to be the way the circuitry is mapped as opposed to broken keys" your reasoning seems right. So why not have at least, a non-invasive try.

Looking at the schematic, there´s like only one path responsible for all the E keys going from the keyboard to the Keyboard Assigner Circuit. The offending part might be a broken wire/cold solder joint.
Lift the keyboard and look for a green shielded wire going to the KAS board underneath. The central conductor is what carries the note information. According to the manual there´s also a "grass green" wire around; it´s not that one. If it helps, the green wire you´ll be looking for should have a blue wire next to it, or they´re both arranged in a twisted pair or something.
You´ll then have to test that path for continuity.

That´s my best and only shot. Beyond here you better find an experienced tech. The CS50 is a very valuable synth and might be worth the expense.


Thank you for a legitimate response. This information actually helps me and it's why I bothered to register and ask the question in the first place. I will pass this information on and let you know how it goes. The CS-50 will absolutely go to a tech but it helps for us to narrow down the cause.

Friend, for what it might be worth to you, I'm actually a really nice guy but I have an extremely low tolerance for ego or for b.s. I came here friendly with zero pretense about what I knew or didn't know on the subject of CS-50s. I detest those who fault others for what they don't know when my actual pursuit was to learn something. I didn't register in this forum to have some vet of this place tell me to go RTFM or smugly suggest that I don't. That's obvious information. I came here to find out if anyone had prior experience on this problem so we could get to the solution more efficiently without getting lost in user manuals.

You took the time to offer some very well thought out suggestions. Thank you. I will be sure to let others who may be interested in the issue know as the problem is fixed.
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Re: Yamaha CS-50 All Keys of E not working

Postby madtheory » Wed Jul 05, 2017 9:59 am

There was nothing smug in my response. You could've just answered the question. Think about it- why would I take the time to look at the schematic for you, when you stated you "didn't know the circuitry"? It's easy to look it up, but you didn't know that. Ironically your response is textbook egocentric- taking it personally, assuming we should know your background, and ad hominem. Best of luck with that.
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Re: Yamaha CS-50 All Keys of E not working

Postby wizardmix » Wed Jul 05, 2017 7:30 pm

madtheory wrote:There was nothing smug in my response. You could've just answered the question. Think about it- why would I take the time to look at the schematic for you, when you stated you "didn't know the circuitry"? It's easy to look it up, but you didn't know that. Ironically your response is textbook egocentric- taking it personally, assuming we should know your background, and ad hominem. Best of luck with that.


I came onto this forum asking if anyone had prior knowledge of this problem and a quick reference for the solution. I didn't ask or want someone to look in a service manual. I view forums as a place where people of likeminded interests come to share their knowledge and experiences. Part of my process in solving something is to see if anyone had already been in the same situation. So I took offense in the idea that if you had nothing to contribute other than to say "Read the service manual" and "Take it to a tech," why comment at all? To me that comes off as being smug. In spite of that, I'll completely volunteer that I may have misread you. If your intent was to be genuinely helpful and in no way short, dismissive or smug, I offer my apology to you.

We're all hypocrites every now and again, admitting that is a part of shedding the ego. I'm a chief offender. I rarely name call so it's ironic to me as well that when I do, partly in sarcasm, of course the intended is a logician blasting everyone's favorite fallacy back at me.
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Re: Yamaha CS-50 All Keys of E not working

Postby madtheory » Wed Jul 05, 2017 9:21 pm

What you didn't anticipate is that it's a complex synth, full of CMIOS chips. This means that there is no straightforward set of symptoms with a particular cause. No typical faults with these synths. Just lots of odd stuff caused by rotting CMOS. And there's a lot of it in there.Analysis of the circuit, in the service manual, is the only way to solve a problem.

Take a look at any of my posts, always helpful, always trying to learn about classic electronics. Don't make assumptions based on a misunderstanding. I accept your apology, good luck with the synth and I hope you find a good tech. Would be interesting to know what caused the fault of you can come back and tell us!
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Re: Yamaha CS-50 All Keys of E not working

Postby Mooger5 » Wed Jul 05, 2017 10:11 pm

That´s the spirit, guys. Now shake hands and get back to troubleshooting.
I´m 90% sure the fault is caused by bad wiring/soldering going from the keyboard diode matrix to the KAS board.
I can provide the diagrams on which my reasonings are based, but it´ll take some time...
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Re: Yamaha CS-50 All Keys of E not working

Postby Mooger5 » Wed Jul 05, 2017 11:25 pm

IC1, the key coder and assigner, has four ports for the octaves U1, U2, U3 and U4; and thirteens ports for the semitones, or individual notes in the keyboard, the 13th port belonging to the lowest C. They´re like the coordinates for each of the 49 keys.
The way the switch and diode matrix is arranged is pretty straightforward, so when we follow those lines we see that:
If the contact for say the highest E note failed, all the notes but that specific one would still work;
Ditto for the corresponding diode;
If the line before the contacts corresponding to the octave of that E note (U4) failed, not only that note but all the others pertaining to that octave would fail too.
If the line past the diodes corresponding to that E note fails, all the E notes fail too. It´s this line that starts in the diode matrix PCB that ends up in the tab for the corresponding IC1 port in the KAS PCB.

More to follow.

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Re: Yamaha CS-50 All Keys of E not working

Postby Mooger5 » Wed Jul 05, 2017 11:43 pm

The KAS board is the large PCB. Notice the white rectangles with the black centered squares.
Those are IC1 and 2, two of many Yamaha custom chips. Notice the million wires, all soldered. Not a single connector in sight. Of all those, only one, a lime green one, carries the E line. Image
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Re: Yamaha CS-50 All Keys of E not working

Postby Mooger5 » Thu Jul 06, 2017 12:02 am

Final post for today (yawn).

Part of the KAS PCB layout. Notice the C, C#, D, D# notes and so on. Also notice the multitude of Es! Which one is it? It´s the one that leads to pin 11 of IC1. Notice how all the other Es are linked by jumper wires. I think "E" here, apart the musical note, stands for Earth. They of course meant Ground points. The shields of the wires are soldered to them. The central conductor of the lime green wire is soldered to the relevant E note.
I speculate, but it´s possible during a previous service job some tech soldered the E green wire to one of the Earth points by mistake, if they are labeled in the PCB like they are in the service manual.

Cheers.

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Re: Yamaha CS-50 All Keys of E not working

Postby Rasputin » Thu Jul 06, 2017 12:27 am

Mooger, as always, you're a rock star. :D

Not my thread, and I have nothing real to contribute, but it's nice to see someone always bring the goods.
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Re: Yamaha CS-50 All Keys of E not working

Postby wizardmix » Thu Jul 06, 2017 1:51 am

madtheory wrote:What you didn't anticipate is that it's a complex synth, full of CMIOS chips. This means that there is no straightforward set of symptoms with a particular cause. No typical faults with these synths. Just lots of odd stuff caused by rotting CMOS. And there's a lot of it in there.Analysis of the circuit, in the service manual, is the only way to solve a problem.

Take a look at any of my posts, always helpful, always trying to learn about classic electronics. Don't make assumptions based on a misunderstanding. I accept your apology, good luck with the synth and I hope you find a good tech. Would be interesting to know what caused the fault of you can come back and tell us!


My friend was the crazy one who bought the (mostly working) CS50, not me :D I'd only go there myself or into CS80 Territory if I could afford it + the cost of a complete refurb, not done by me. I'd also like to be able to walk when I'm in my 70s -- those things get close to Rhodes/B3/C3/A100 territory in weight. I compromised and got a new Vermona Perfourmer MKII instead. A worthy contender to those who don't want to deal with the volatility / weight / price of a CS50 or Eight Voice but perhaps sacrileg in a forum such as this.

I will absolutely share the results of this undertaking. Thanks and no hard feelings!
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