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Yamaha CS-50 not playing notes

Posted: Tue Dec 23, 2014 10:08 pm
by nooel
Hi all-

This is my first post. I just received a Yamaha CS-50 yesterday in the mail that I paid $1350 for. After setting it up, I plugged it in and it played fine for about 10-20 minutes, before not sounding any notes. Does anyone know what the problem might be?

I've gathered that it is the KAS board (key assigner), and could very well be the YM26700 chip itself, which I hear is really expensive. That being said, I've also read that the 4000 series CMOS chips are prone to failure due to their age. There was a forum post that suggested that sometimes people will mistake a faulty 4000 series (in the case of the forum post, the 4016's) CMOS failure for YM26600 and YM26700 failures.

This is particularly frustrating because I was told the synth was fully functional (which it was for about 10-15 minutes), but it is likely the case that this item sat in some storage for many years, and was likely not thoroughly tested to determine it's condition. I'm considering filing a PayPal complaint, as I just paid for a $1350 synthesizer that could very well be essentially totaled within minutes of receiving, and the seller said he does not accept returns.

Does anyone know if I'm screwed or if there is hope in failed CMOS 4000 chips? The problem, as far as I can tell, is the outputs of the YM26700 are stuck at ground, is that a failed chip or something else potentially?

Re: Yamaha CS-50 not playing notes

Posted: Tue Dec 23, 2014 11:33 pm
by Steve Jones
Change the 4000 series CMOS in any case. They need to be replaced after this number of years and they are cheap so whether you do have to change the key assigner or not these chips will need to be replaced if you want the machine to be more reliable.

Re: Yamaha CS-50 not playing notes

Posted: Wed Dec 24, 2014 2:18 am
by synthparts
Then again if you paid for a synth that was supposed to be working and wasn't I'd do the Paypal and/or eBay dispute process rather than messing with it... Once you open it up the seller can claim you tampered with it...

Re: Yamaha CS-50 not playing notes

Posted: Thu Dec 25, 2014 8:47 pm
by nooel
Thanks for your input guys. Does this sound like a dead YM26700, dead CMOS chips, or it's hard to say one way or another?

I do intend on following both of those pieces of advice, but I think regarding the PayPal claim, I might see of I can settle on a cheaper price, since I do obviously want one of these synths, and I paid $1350 for a fully functioning CS-50. So I guess I'm trying to assess the possible additional costs I will incur in the repair of this beast so I know where a reasonable settlement between myself and the seller is.

Re: Yamaha CS-50 not playing notes

Posted: Sat Dec 27, 2014 1:21 am
by Synthetech
You won't know anything until you get a schematic in one hand and a scope probe in the other.. then start checking the outputs and inputs around the chips.

There are so many components besides the chips that can cause issues.

It's going to cost at least $250 or more for a tech to get in there and start diagnosing.
Then you have parts and labor on top of that to do the needed repairs.

I'd guess the bill will be around $750 by the time it is fixed.. more if it is recapped and other common restoration work done too.

So your refund better be about 750 or more to make it worth messing with getting fixed.

And don't expect it to be fixed in two weeks... try more like 4 months or longer. This is typical for synth repairs as extensive as this one appears to need.

Re: Yamaha CS-50 not playing notes

Posted: Sat Dec 27, 2014 9:37 pm
by db0451
but there is not yet any definition of what "this one appears to need". that's what he's looking for. scoping and such is always the best idea, but surely someone else knows whether the CMOS could be at fault, or it's definitely a duff KAS, or something else? it may take a while to get to the front of a good tech's queue, but it's not necessarily as bad as 4 mo

it might end up being best to seek a full refund, but maybe not, so it's best to try to get all the info. if lucky, he might get something like what happened with my MKS-30, where the seller was extremely helpful and provided a mammoth refund that covered not only a tech fixing the chips/replacing one, but also the postage both ways and a bit to spare.

Re: Yamaha CS-50 not playing notes

Posted: Sat Dec 27, 2014 11:48 pm
by Synthetech
db0451 wrote:but there is not yet any definition of what "this one appears to need". that's what he's looking for. scoping and such is always the best idea, but surely someone else knows whether the CMOS could be at fault, or it's definitely a duff KAS, or something else? it may take a while to get to the front of a good tech's queue, but it's not necessarily as bad as 4 mo.

how is anyone going to know what is wrong with it without reading the schematic, get familiar on how the CS is supposed to work and begin probing it out for proper signals, power, audio....?
if the CMOS chips dont get power, they will not function.
it does not mean the CMOS chip is defective.. it means it is not getting a connection to the power source.
h**l, it could even be a small chink of semiconductive or fully conductive material that is resting on the circuit board that cannot be seen.. wedged inside against a couple pins of an IC or making a small short across a diode.. I've had that happen to me before and it will drive you crazy! Especially when it moves around and causes the old problem to fix on it's own and a new problem surfaces in it's place.

even if a well versed CS-** tech has worked on a bunch of these, he's going to begin at square one just like anyone else with a unit that simply will not make any sounds.
the only way he's going to be certain it is a chip is to TEST that chip for signals going in/out and power.

it's real simple, ANY TECH in their right mind will say they must see and test the unit themselves.
once they do tests, THAT COSTS MONEY!.., THEN and ONLY THEN can they even begin to be more certain to say if its a chip, a diode a resistor, capacitor, connector...
until then, it's all as educated a guess as "pin the donkey" on the schematic.


4 months is not unusual for a tech who is a vet at fixing CS's. He is going to be in high demand and have quite a few units ahead.. once he finishes them (or gives up on them for a period..) then he'll diagnose the unit, locate the apparent problem, check with the owner on repair suggestions.. then order parts.. then try to fix it.. then if it isnt fixed right away, set's it to one side and works on another to try and make money... then return to the problem synth again later on AFTER HE HAS MADE MONEY OFF ANOTHER REPAIR.
after that, he will try to have another go at fixing it..
That usually sums up to at least 4 months, if not more.
you should hear the stories of how long it takes to get a vintage synth repaired.. it's crazy!

So I say again,

plan on at least $250 for someone who knows what they are doing to tell you what the actual problem is.
then another 250-500 to fix it.. or more

if the seller refuses to give a partial refund of at least ~$750, then I highly suggest making a paypal claim for a full refund.

Re: Yamaha CS-50 not playing notes

Posted: Sat Dec 27, 2014 11:53 pm
by Steve Jones
db0451 wrote:but there is not yet any definition of what "this one appears to need". that's what he's looking for. scoping and such is always the best idea, but surely someone else knows whether the CMOS could be at fault, or it's definitely a duff KAS, or something else?

There are many things that it could be other than the KAS board. If it's not sounding any notes why assume that it's the key assigner? It could be a failed power supply rail, it could be a faulty output stage, could be anything.

Re: Yamaha CS-50 not playing notes

Posted: Sun Dec 28, 2014 3:45 am
by nooel
First of all, just wanted to say thanks to everyone for taking the time to add their input.

0V on the TU input on the KAS board (that sets voltages for the octave and note ladders), you can guess where this one is heading…

Got 6 mV on the + 15V rails, -15V was bad too. With both fuses intact I figured it wasn't a short, and knowing that the 4000 series CMOS are suspect, I flicked the 4558 to see if I could pop it back closed (assuming since it was working before that it couldn't be that far open). Turned on the CS-50 and it worked for about 30 seconds and then went back to silent, 6 mV on the rails.

Again, thanks to everyone who contributed. I would like to add, for any future Yamaha CS-50/60 owners who stumble across this thread, Steve Jones is very correct in saying that it makes a lot of sense to go in and replace the CMOS chips and the caps. When you are talking about $1000+ proprietary chips, you don't want $2 chips that are known to age poorly taking one out.

Finally, Old Crow/Scott Rider, if you ever run across this thread, I know you re-did the KAS for a CS-15, and had worked out a new KAS with updated parts for the CS-50/60/80(?) earlier in the decade. I would love to lend any assistance to helping complete that project, and would gladly buy 3 in a group buy if the board is ever completed. I don't know how prevalent YM26600 and YM26700 failures are, but it's really a shame that one chip can essentially total these beautiful old synths.

Re: Yamaha CS-50 not playing notes

Posted: Wed Mar 02, 2016 1:29 pm
by m_P
Hello there.

Did you get any further with this?
I just recently bought a CS60 which is playing notes erratically, and only seems to be triggering notes from the very top octave.
Whenever I press notes in the lower octaves, they either don't trigger, or trigger much later than when the key has been pressed.

I'm fearing the worst - but have lined up a tech to go through it so we will see..

I too would be interested in the Old Crow KAS board for my CS-60 too.. :cry:

Re: Yamaha CS-50 not playing notes

Posted: Wed Mar 02, 2016 4:20 pm
by nooel
m_P-

I was able to fix mine. It ended up being a cracked trace in the PSU, shutting down the whole party.

I do remember mine being a big scare because the proprietary chips are so expensive. However, I think the chips are generally very robust and it is hopefully not the issue. If it is, there may definitely be options out there already, including possibly the Kenton retrofit.

To start from the top I'm assuming you experience this with any of the octave selectors depressed?

Re: Yamaha CS-50 not playing notes

Posted: Thu Mar 03, 2016 9:53 am
by m_P
Thanks for responding nooel.

So the keys from D4 to the top of the keyboard, it triggers the notes as it should.
When I change the octaves on the panel, the pitch changes accordingly.
Anything below D4 plays the notes with a huge delay and overlap. Sounds like garbage.

Many of the voices aren't actually triggering in cycle now - just silence.
They were all working when I first tested the machine.. But after a few hours various ones stopped.

I'm hoping it's something other than those proprietary chips.
Taking her to a tech today. The information on here has been invaluable though, thank you.

Re: Yamaha CS-50 not playing notes

Posted: Sun Mar 06, 2016 7:10 pm
by nooel
They were all working when you first got the machine? That's great news, it likely means heat is the culprit. Could very likely be a cracked trace like mine.

Let me know if you need any further info. When mine went down, I got copies of the service manual and schematic (for the CS-50, which is identical to the CS-60, just with less voices). I understand the schematic pretty well, so if you guys get stuck I could probably give a couple suggestions.

Good luck

Re: Yamaha CS-50 not playing notes

Posted: Mon Mar 07, 2016 10:14 am
by m_P
Thanks Nooel,

Yeah it was weird, I tested it in a cold place and played on it for about 30 minutes - everything was fine.
I picked it up 2 days later and once I got it home it started going weird.

I then left it on for a day or so and it played almost perfectly.. Then it just started going crazy.

I too think heat might be the issue. It all definitely points towards to KAS board.

I've sent through the schematics to my tech, so he'll see what's going on, but any extra info you might have would be great. Thank you

Re: Yamaha CS-50 not playing notes

Posted: Mon Mar 21, 2016 6:40 am
by raycastile
I'm in the market for a CS60, and discussions like this scare me. Not enough to dissuade me from pursuing my "dream" synth, but they definitely give me pause.

I'm in the St. Louis, Missouri, area. I notice a lot of the online vintage synth culture seems to be based in Europe, especially the UK. Does anyone know of reliable sources for vintage synth repair in the mid-western United States? Particularly people who would know how to service something like a CS synth?