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Yamaha CS 60 - pitch drops on release
Old 1 week ago
  #1
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Emanuel23's Avatar
 

Yamaha CS 60 - pitch drops on release

On certain voices of my CS 60, the pitch drops during the release time.

During the Attack / Sustain / Decay times the pitch is perfect. But come Release, and the pitch gently drops on voices 3 & 4 - or it becomes slightly detuned on voice 7 and possibly another one. All other voices retain their pitch, although ever so slightly off on some.

Anyone have an idea what it might be?

- The Portamento / Glissando function is switched off, so that can not be it;
- as far as I can test, all other functions of the synth work.

I'll make a video of it soon.
Old 1 week ago
  #2
Gear Maniac
 

The S&H caps are probably leaky. Had the same thing on my CS-40m.
Old 1 week ago
  #3
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adhmzaiusz's Avatar
Quote:
Originally Posted by Emanuel23 View Post
On certain voices of my CS 60, the pitch drops during the release time.

During the Attack / Sustain / Decay times the pitch is perfect. But come Release, and the pitch gently drops on voices 3 & 4 - or it becomes slightly detuned on voice 7 and possibly another one. All other voices retain their pitch, although ever so slightly off on some.

Anyone have an idea what it might be?

- The Portamento / Glissando function is switched off, so that can not be it;
- as far as I can test, all other functions of the synth work.

I'll make a video of it soon.
My cs50 and another one I saw did this too. It’s annoying because it drops pitch enough that it just sounds out of tune.

I have a suspicion that it is a matter of cleaning the key contacts.
Old 1 week ago
  #4
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Quote:
Originally Posted by adhmzaiusz View Post
My cs50 and another one I saw did this too. It’s annoying because it drops pitch enough that it just sounds out of tune.

I have a suspicion that it is a matter of cleaning the key contacts.
Interesting regarding the CS 50; always good to know I'm not alone. It is definitely not the key contacts: they are as good as new for one thing, and that is not how the CS series work anyway. It has to be something in the electronic circuitry / control voltage.

Quote:
Originally Posted by GAF Vu Master View Post
The S&H caps are probably leaky. Had the same thing on my CS-40m.
GREAT suggestion! Measuring on the K1 ~ K8 output pins of the SH board show the voltage gradually dropping on the suspect voices! Awesome.

To be complete; the output of the KAS board is fine - as it feeds the SH-board I wanted to be sure that the SH-board received proper voltages to begin with. That is indeed the case.

During the restoration a while back I replaced all ceramic and elco caps on that SH board, so it must be the foil caps. There are 3 foil caps per voice; one larger green cap, a smaller green cap, and a yellow cap. Some pictures and a schematic attached. My hunch is that it's the yellow ones. They look a bit shabby, and afaik green caps last a long time - however on another synth I restored recently I did run into a faulty one, not unlike the smaller 103K50 here.

The values of all of these foil caps measure out within tolerance though, see photo's attached. I feel inclined to go ahead and replace all of them with box / film caps. On the other hand I'd like to keep the green caps if possible.
Attached Thumbnails
Yamaha CS 60 - pitch drops on release-sh-caps-01.jpg   Yamaha CS 60 - pitch drops on release-20190809_091631.jpg   Yamaha CS 60 - pitch drops on release-20190809_091645.jpg   Yamaha CS 60 - pitch drops on release-20190809_092352.jpg   Yamaha CS 60 - pitch drops on release-20190809_091826.jpg  

Yamaha CS 60 - pitch drops on release-20190809_092035.jpg   Yamaha CS 60 - pitch drops on release-20190809_092104.jpg  

Last edited by Emanuel23; 1 week ago at 09:18 AM.. Reason: layout
Old 1 week ago
  #5
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Quick update: I Interchanged the foil caps on the SH board from a bad voice with a good one. Turns out it is neither of them. Then I did the same with the ceramic caps and the CA3140T opamps. Still the issues remained on the exact same voice. Double checked the input of the SH board: fine. Double checked the output: faulty / dropping still. Interchanged a set of 3 foil caps from channel 1 to 3; still the very same voice board (3) outputs the very same release pitch drop. Even went as far as changing a 4016 chip - makes no sense, but at this point what else could it be? Issue remained, no change whatsoever.

Interesting note: when measuring the 4016 chip I found that connecting the multimeter probe on one of the output pins, it would affect how fast or slow the pitch would drop on that output channel.

Could it be that the output of the SH board actually reads what it is receiving from the voice M-board, like some kind of feedback? It arrives at the M-board on pin (37), and is connected to:

+ the VCO IG00153 pin (2) of IC8
+ IG00156 (VCF HPF) pin (2) of IC10
+ IG00156 (VCF LPF) pin (2) of IC11
+ there's a K cap also on there; these K caps were recapped recently so they are brand new caps.

==> Reply to that last question: NO .. I detached the feed for M-board 3 from the SH board, and saw the pitch dropping still with no connection attached.

To repeat: with the release on its shortest setting, there's no issue whatsoever, all voices sound fine.

And one more thing: when starting up the CS60, all voices sound simultaneously IF the release time is set high. All I have to do is put the release time down, and they stop. Seems to be related.

Last edited by Emanuel23; 1 week ago at 09:21 AM.. Reason: layout
Old 1 week ago
  #6
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Well, whatever you do discover keep us posted. I have too many synths to work on right now to even find room to work on my cs50.. so hope you do make some progress!

I can see why you’d be looking at the s&h circuitry... but to elaborate a little more I think there is a double triggering happening that is too fast for the key assigner to compute and it’s causing a pitch drift on release. And while yours might still look new, I wouldn’t trust any 40+ year old keybed lol. Looks like there is a busbar and leaf contact type mechanism, I would personally make the busbar my starting point before guessing anywhere else.
Old 1 week ago
  #7
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Quote:
Originally Posted by adhmzaiusz View Post
Well, whatever you do discover keep us posted. I have too many synths to work on right now to even find room to work on my cs50.. so hope you do make some progress!
Will do!



OK, so I've ordered new box caps anyway for all positions on the SH board, figured it won't hurt.
Will keep you posted when I receive and install them.

It is most notable on voice 3; here is a video of the issue:

Old 1 week ago
  #8
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Quote:
Originally Posted by Emanuel23 View Post
Will do!



OK, so I've ordered new box caps anyway for all positions on the SH board, figured it won't hurt.
Will keep you posted when I receive and install them.

It is most notable on voice 3; here is a video of the issue:

After hearing your video, that's definitely different than the problem I was imagining... or a little more intense than my issue.

So you say in the KAS circuitry the gate/integrator/buffer (IC9-20) seems to all check out ok? Did you check diodes 19-34? Looks like there is a lot to consider in the overall schematic and hard to really offer ideas without seeing it in person..
Old 1 week ago
  #9
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audiohub's Avatar
 

What does the board look like on the bottom (trace side)?

All analog S/H circuits are sensitive to board contamination like flux and other contaminates around the sensitive pins of the opamp. It's vital that the whole area is as clean as possible for the circuit to work correctly.
The circuit works by charging up a cap ( those .22uf green caps on your unit) to a voltage that sets the pitch of the oscillator. When the key is released that charge on the capacitor keeps the voltage constant so the pitch does not drop or droop. Flux or other dirt around it will try to drain off this charge, causing the pitch to droop over time.
A well designed board will have a "guard ring", a trace that surrounds the sensitive cap and opamp input parts, and is connected to the output of the opamp, which greatly reduces the chance for drift, but not all manufacturers do this.

Try cleaning the underside of the board with flux remover (I usually use pure (100%) acetone and a Q tip or cotton ball), and make sure that there's no contamination left on any of the solder connections, connector or IC pins, or between any of the traces. Make sure the top is cleaned of any gunk or residue as well.
DO NOT use electrical contact cleaners (Deoxit, etc), as these leave behind residue that will actually make the problem worse.
This may solve your problems.
Old 1 week ago
  #10
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Quote:
Originally Posted by adhmzaiusz View Post
So you say in the KAS circuitry the gate/integrator/buffer (IC9-20) seems to all check out ok? Did you check diodes 19-34? Looks like there is a lot to consider in the overall schematic and hard to really offer ideas without seeing it in person..
I haven't checked the diodes, but YES all CA3140T opamp outputs on the KAS board are stable and they feed the SH board a fixed voltage across the board.

Quote:
Originally Posted by audiohub View Post
Try cleaning the underside of the board with flux remover (I usually use pure (100%) acetone and a Q tip or cotton ball), and make sure that there's no contamination left on any of the solder connections, connector or IC pins, or between any of the traces. Make sure the top is cleaned of any gunk or residue as well.
DO NOT use electrical contact cleaners (Deoxit, etc), as these leave behind residue that will actually make the problem worse.
This may solve your problems.
Thank you sir, I did as you suggested and although voice 3 is still in freefall during Release, the overall pitch of the other 7 voices is more stable. Not perfect though, but there's a noticeable improvement!

Some photo's attached.

I'm hoping the new foil / box caps will do the trick; I'm receiving them on Monday and I will report back.

Although interchanging the CA3140T opamp of (faulty) voice 3 with the opamp on (proper functioning) voice 1 did not result in a different result, I am keeping a weary eye on those 3140 opamps. They have troubled me in the past. I replaced all of the original ones with CA3140 parts from UTSource, branded Harris. I found the replacements to be FRAGILE; bending the legs to stretch them across the designated footprint of the SH-board rendered a lot of them non functioning.
Attached Thumbnails
Yamaha CS 60 - pitch drops on release-20190810_103159.jpg   Yamaha CS 60 - pitch drops on release-20190810_103206.jpg   Yamaha CS 60 - pitch drops on release-20190810_103216.jpg   Yamaha CS 60 - pitch drops on release-20190810_103847.jpg   Yamaha CS 60 - pitch drops on release-20190810_103900.jpg  


Last edited by Emanuel23; 1 week ago at 09:23 AM..
Old 1 week ago
  #11
Gear Head
 
audiohub's Avatar
 

Hey, sounds like you're making some progress here, which is a good sign.

I'm assuming that your S/H circuit is being fed by a group of CD4016 analog switches, and I noticed that you mentioned earlier that the pitch dropped faster when you probed the pins there, which is to be expected (the meter has resistance which helps drain the charge on the S/H cap when connected).
It looks like these switches are in sockets (can't see them very well in your pics) and that may be part of your problem as well.
Sockets are notorious for collecting and holding flux and contamination, and this circuit is just as sensitive as the CA3140 opamps (it is also connected directly to the S/H cap, and can just as easily drain the charge on that cap. The 4016s also have a track record of going bad over time, especially in sensitive areas like this).

It looks like you did a great job cleaning the bottom of the board, this is just what it should look like to work its best, and it looks like it has been some help here.

I would suggest getting rid of the 4016 sockets and soldering a NEW set of these analog switches right on the board. Be sure to clean the top and bottom of the board both after you have removed the sockets and chips, and again after the new ones have been installed to make sure that there is no residue left around the pins. Make sure that all residue is cleaned off the top of the board as well, and remove any flux between IC pins and any of those wire jumpers on the top of the board.

Your aim is to eliminate anything (flux, dirt, grease) that might be able to drain off the voltage charge on that green .22uf S/H cap. These caps typically don't go bad although there can be rare exceptions. The cuprit is more likely dirt or flux in a sensitive area possibly around those 4016s, (or maybe a leaky 4016 itself) since the bottom is now so nicely cleaned.
Old 1 week ago
  #12
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drockfresh's Avatar
Quote:
Originally Posted by Emanuel23 View Post
On certain voices of my CS 60, the pitch drops during the release time.

During the Attack / Sustain / Decay times the pitch is perfect. But come Release, and the pitch gently drops on voices 3 & 4 - or it becomes slightly detuned on voice 7 and possibly another one. All other voices retain their pitch, although ever so slightly off on some.

Anyone have an idea what it might be?

- The Portamento / Glissando function is switched off, so that can not be it;
- as far as I can test, all other functions of the synth work.

I'll make a video of it soon.
If you want help Jeff B from the Analog lab does remote sessions and he is a master tech who can fix anything (even a rare Moog my local tech said was unfixeable and gave back to me). It could save you lots of time.

D
Old 1 week ago
  #13
Gear Addict
 
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Quote:
Originally Posted by drockfresh View Post
If you want help Jeff B from the Analog lab does remote sessions and he is a master tech who can fix anything (even a rare Moog my local tech said was unfixeable and gave back to me). It could save you lots of time.

D
Unfortunately I'm not in the US, great tip though!

Quote:
Originally Posted by audiohub View Post
It looks like these switches are in sockets (can't see them very well in your pics) and that may be part of your problem as well.
Sockets are notorious for collecting and holding flux and contamination, and this circuit is just as sensitive as the CA3140 opamps (it is also connected directly to the S/H cap, and can just as easily drain the charge on that cap. The 4016s also have a track record of going bad over time, especially in sensitive areas like this).
Correct, they are on mill-max sockets with integrated cap between pin (7) and pin (14). When reading up on Old Crow's CS80 restoration, he advised to use these sockets; some photos attached. (The SH board photo does not reflect its current condition though, I took that one during the restoration last year).

Will do as you say and report back!
Attached Thumbnails
Yamaha CS 60 - pitch drops on release-20181209_220234.jpg   Yamaha CS 60 - pitch drops on release-20181211_165528.jpg  
Old 1 week ago
  #14
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Quote:
Originally Posted by Emanuel23 View Post
Unfortunately I'm not in the US, great tip though!



Correct, they are on mill-max sockets with integrated cap between pin (7) and pin (14). When reading up on Old Crow's CS80 restoration, he advised to use these sockets; some photos attached. (The SH board photo does not reflect its current condition though, I took that one during the restoration last year).

Will do as you say and report back!
Jeff will Skype with you. He does has a “tech for techs” service if he has the time.
Old 6 days ago
  #15
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Quote:
Originally Posted by drockfresh View Post
Jeff will Skype with you. He does has a “tech for techs” service if he has the time.
Good to know! I'll keep Jeff as a back up for when things really get stuck.
I did the restoring of this CS 60 myself so far, I want to see it through all the way as much as I can ;-)

ALRIGHT update!

I noticed a MAJOR improvement after: 1) cleaning the top of the board with acetone, 2) removing the sockets from the 4016's and soldering the chips directly onto the board, and 3) replacing all 24 foil caps with new ones.

The pitch now only drifts on these voices:

- voice 3: still a noticeable drop; enough to be annoying, but far less severe as it was
- voices 4 and 8: slight drop
- voices 5 and 6: minor drop, hardly noticeable

Some photos attached, and here's a video:



With all of the foil caps and 4016 chips + sockets removed, I scrubbed the board on all sides with a toothbrush and 100 % acetone. I got into most gaps BUT it was hard to get in between the legs of the CA3140T opamps; might revisit this challenge with a cue tip.

So now onto fixing that last couple of drops! Could the variable resistors be playing a role in this? EVERYTHING is NEW on my SH board at this point, except for the wire jumpers + that one 22K resistor + those 8 variable resistors. Oh and the 4011 chips are still on sockets, but they read out fine.
Attached Thumbnails
Yamaha CS 60 - pitch drops on release-20190814_095803.jpg   Yamaha CS 60 - pitch drops on release-20190814_101023.jpg   Yamaha CS 60 - pitch drops on release-20190814_101015.jpg   Yamaha CS 60 - pitch drops on release-20190814_101029.jpg   Yamaha CS 60 - pitch drops on release-20190814_101033.jpg  

Yamaha CS 60 - pitch drops on release-20190814_102110.jpg   Yamaha CS 60 - pitch drops on release-20190814_102953.jpg   Yamaha CS 60 - pitch drops on release-20190814_102956.jpg   Yamaha CS 60 - pitch drops on release-20190814_105804.jpg   Yamaha CS 60 - pitch drops on release-20190814_105814.jpg  


Last edited by Emanuel23; 6 days ago at 02:12 PM.. Reason: Cla
Old 3 days ago
  #16
Gear Head
 
audiohub's Avatar
 

Great to hear that you’re making progress!

Now, for your still-drifting voices, I was looking at the bottom shots of your board and noticed that there are some spots where leads are bent over and are touching other traces that are going by. I see one for that sensitive trace for voice three. Even though it’s not actually shorting to the trace because of the green etch resist enamel that covers the traces, it still may be providing a path to discharge that sensitive capacitor.
I see these types of bent over leads in several places, and would trim them all to clean things up. You want everything to be as isolated here as much as possible. Think of the capacitor here like a bucket, getting filled up with an electrical charge that becomes the pitch of your note when the key is released. Any contamination around this bucket is like a leaking hole, draining that bucket and making the pitch drift. Gotta find and plug that leak.

A few more thoughts....now that you’ve cleaned away the flux that was contributing to your drift problem, and things have improved, you may find that some drift is still coming from the opamp. You mentioned replacing it before, but any improvement gained from replacing it may have been obscured by the effects of flux and other board contamination. It might be worth installing a new device here (and re-cleaning of course) to be sure.

Also, if you haven’t done so already, now that the board has been initially cleaned, use some cotton balls and acetone to do a fine clean on the surfaces. Cotton balls do a good job of sucking in, picking up and holding any residual flux, etc that you can’t see. Change the cotton balls often, and concentrate on the top and bottom of that sensitive area of the S/H circuit. If things are still drifting, it means that there is some sort of path around that sensitive area that is draining the charge off of that .22 uf capacitor. Finding what that path is will be the key to fixing the problem. I would do several passes this way, using a hair dryer or hot air gun (sparingly) in between each to make sure everyting is dry and evaporated before starting again.

I was suprised at how poorly that board was designed. Looking at the layout of the board in the service manual, there is no “guard ring” around that sensitive capacitor like I mentioned earlier. In fact, the traces surrounding that sensive point are connected to the negative voltage supply, and this would cause the output to drift down if given half a chance by any surrounding contamination. Certainly not an ideal situation!

You can read more about the guard ring technique here:
http://www.ti.com/lit/an/snoa664/snoa664.pdf
Since your board doesn't incorporate any of these techniques, things will have to be as sparkly-clean as possible to get decent performance.

Sounds like you’re getting really close! Good luck!

Last edited by audiohub; 3 days ago at 03:23 AM..
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