Solved! CASIO CZ-5000 distorted output

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Yekuku
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Solved! CASIO CZ-5000 distorted output

Post by Yekuku » Sat Jan 23, 2021 1:40 pm

Hi guys,
Well it looks like that it took me some time, but I have just joined the CZ-5000 cult!
I bought an unrepairable unit for a good price, hoping that I could repair it.
The unit sounds distorted (digital harsh) on all outputs.
I suspected the infamous relay, but after bypassing it , the issue remains.
I have not done anything else yet, I just thought to share my excitement and ask for help from the experienced CZ users.
Did anybody have similar issues ? Any ideas what the culprit can be ?
I am suspecting Ram issues, because I had similar experience with a DX7, but I would like to hear what you think.
many thanks!
Last edited by Yekuku on Sun Mar 07, 2021 1:35 pm, edited 1 time in total.
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madtheory
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Re: CASIO CZ-5000 distorted output

Post by madtheory » Sun Jan 24, 2021 7:59 pm

I think I know this sound. Kinda gritty, low bit depth effect? Try adjusting the DAC offset. Page 59 of CZ-1 manual (same thing as CZ-5000 in this case). IIRC you have to remove the keyboard to get at this VR.

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Re: CASIO CZ-5000 distorted output

Post by Yekuku » Sun Jan 24, 2021 8:36 pm

Thank you for your reply Tomas.
Unfortunately adjusting VR2 does not have an effect on sound.
VDAC is 4.8V which I think is the problem.
Checking the PSU without load the VDAC is 5.2 V which I think is good, when connected to the mainboard it drops to 4.8V.
I tried to track where VDAC is used and it feeds the VR2 which is in feedback loop of the opamp after the DAC. It looks like the VDAC feeds only passive components, I wonder why there is this voltage drop. Could it be that a resistor on the DAC circuit has gone up in value and is pulling more current ?
Or is the problem in the PSU which generates the VDAC ?
Any ideas?


UPDATE: VDAC also feeds the expander and sample & hold circuits, I ll have to check these ICs too.
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Re: CASIO CZ-5000 distorted output

Post by madtheory » Mon Jan 25, 2021 11:48 am

Good call, yes, I guess it could be anything in that circuit?

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Re: CASIO CZ-5000 distorted output

Post by Yekuku » Tue Jan 26, 2021 10:13 am

Well, since I dont have proper understanding of what is going on , on the expander and S&H ciruit, I replaced all ICs there, ( 4051,4053,082) but nothing changed. VDAC remains at 4.8V.
My thoughts are on the power supply, I tested the zeners and they look ok , I went out shopping yesterday for 2SC1815, and I was surprised to find out that they go for 2.5 euro per piece ! CRAZY! I used to buy these for a few cents per piece! I did not buy any, I ll try and replace them with a cheaper compatible version.

In the meantime , I have discovered more problems.
- The sequencer is not working
- torn contact strips.
I will deal with these once I repair the distorted output problem.
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Re: CASIO CZ-5000 distorted output

Post by madtheory » Wed Jan 27, 2021 11:57 am

Yekuku wrote:
Tue Jan 26, 2021 10:13 am
- The sequencer is not working
That's a shame. It's a PITA to learn, and there's nothing it does that you can't do in a DAW. The step programming is exactly like step input in Pro Tools! But it is a fun set of limitations to work in. I learned the s**t out of it back in 1990, it was all I had :)

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Re: CASIO CZ-5000 distorted output

Post by Yekuku » Wed Jan 27, 2021 8:01 pm

Ha! Now I am more curious about the sequencer. Gotta fix this and check it out!
I tried also searching for contact strips but I couldnt find any :-/
Do you know of any other keyboard models that use similar strips ?
I will have more news about the power supply repair on the weekend.
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Re: CASIO CZ-5000 distorted output

Post by madtheory » Thu Jan 28, 2021 2:27 pm

I think it is a safe bet that Casio CT series keyboards from around 1985 use the same keybed/ mechanics as CZ. But I've never tested that theory. They're an unpleasant action to use, and get squeaky with age/ use. Although I understand the desire to fix it. FZ-1 and CZ-1 are defo the same keyboard, and it looks to me like the CT-6000 is the same keybed even though the aftertouch is a different mechanism (I have an FZ-1 above a CT-6000 here) and feels even worse IMO. I picked up a CT-430 for €10 without a PSU and two broken keys (it's fixed now and it is cute). So I'm sure you'd pick something up that you could test with.

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Re: CASIO CZ-5000 distorted output

Post by Yekuku » Thu Jan 28, 2021 5:18 pm

Many thanks for the information Madtheory, I deeply appreciate it.
When it comes to Casio , I am a complete noob, the CZ 5000 is my first Casio.
I will research the CT series, I am hoping that they used similar keybeds.
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Re: CASIO CZ-5000 distorted output

Post by madtheory » Thu Jan 28, 2021 10:56 pm

Came across this info about the DAC offset (this is a CZ-1000):
https://zeninstruments.blogspot.com/201 ... NZqARgKKbY

Here is CZ-5000 service manual, text searchable pdf:
https://www.dropbox.com/s/9g6p4d0hdaz87 ... e.pdf?dl=0

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Re: CASIO CZ-5000 distorted output

Post by Yekuku » Tue Feb 09, 2021 9:13 pm

Thanks for the help ;)
So far , no luck. I checked all components on the PSU section that generate VDac and I didnt find any problem, everything tested ok off circuit. Zeners, the usual leaky suspects, work in specs in circuit.
Still VDac is 4.8V, in other circumstances I would not see this as a problem but after researching similar problems on the cz-1000 and cz-101, it looks that Vdac has to be fine tuned to ged rid of the distortion.
The cz 5000 and cz-1 use 1 trimmer for calibrating the Vdac, as they have a dedicated power line coming from the psu.
I am wondering what causes the voltage drop, I have already replaced the ICs that are powered from Vdac.
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Re: CASIO CZ-5000 distorted output

Post by meatballfulton » Wed Feb 10, 2021 3:00 pm

The CZ-5000 was my first synth.

The sequencer is the bomb. Unlike so many sequencers, even in DAWs, in step mode each track can have it's own length so it's possible to create all kinds of fun polymetric behavior. I once set up a song with each track length based on prime numbers...7 bars, then 11, 13, 17, 19, 23, 29, 31. The song would run in a loop for 6,685,349,671 bars before repeating. At 120BPM that would take 154,753 days...423 years :lol:
I listened to Hatfield and the North at Rainbow. They were very wonderful and they made my heart a prisoner.

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Re: CASIO CZ-5000 distorted output

Post by madtheory » Fri Feb 12, 2021 9:23 pm

Ya it's a fun machine. I'd love to hear your track!!!

But honestly, Pro Tools can do exactly the same thing with its step sequencer. Here's a track a hauled out of my CZ-5000 sequencer backups and re-arranged (in Pro Tools as it happens). The basis is step programmed loops of different lengths. Not in years though :lol:


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Re: CASIO CZ-5000 distorted output

Post by Yekuku » Fri Mar 05, 2021 12:29 pm

Well I have been scratching my head for weeks, there is an update but the problem persists.
After checking the PSU and found all components to work as expected, I went ahead and replaced the zener diodes on Vdac 5V line although they were regulating the voltage correctly in circuit.
To my surprise Vdac recovered from 4.8V to 5V , it looks like the zener was regulating the voltage correctly but was hogging down the current. I really hate when this happens , it is impossible to find the affected component unless it gets replaced.
Anyways, the bad news is that even with Vdac at 5V the problem persists, so my assumptions were wrong.
Adjusting the DAC trimmer does not affect sound, it is still distorted.
I am suspecting the DAC ( BA9221) but it could be either one of the 2 MUSIC LSI ics or whatever.
Well , I am fed up with this one, maybe I need to take a break.
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SOLVED ! Re: CASIO CZ-5000 distorted output

Post by Yekuku » Sun Mar 07, 2021 10:50 am

Well we have success !
After replacing the 5.6V zener diode on the PSU and having Vdac recovered to 5V I went back on the DAC circuit and inspected all ICs one by one.
Guess what, it was the expander circuit causing the distortion.
When the Vdac recovered , the distortion persisted but it turned out that it a was different kind of distortion as the low volume portion of the sound sounded ok while the louder portions were distorted. At the time i had just suspicions as I could not compare the 2 different types of distortion at the same time.
This got me thinking that it might have sth to do with the expander circuit, I went ahead and replaced the 4051 ( main expander IC) , and now it sounds ok !
I had replaced the 4051 previously but with the Vdac at 4.8V , the culprit didnt show up back then so I had to put the original 4051 back in place.
On to the sequencer , let me check out what are you talking about guys !
Thank you all for your support!

p.s . If anybody finds any compatible contact strips, i would gladly buy some !
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