Saturday, June 18, 2016

CZ 1000 Noise Fix (DAC Adjustment)

So I picked up an as-is CZ 1000. It started off terribly distorted, but after jumping a few corroded traces it started to sound more normal. Still not right though. Some presets had an odd harshness and some a "zipper" sound as they decayed.

It might not come across on soundcloud, but here's an example.



After some searching I found several people discussing similar problems. Each time the solution was to adjust the DAC's offset voltage. The schematics can be found easily and they depict the DAC portion like this:



VR2 is the obvious candidate, but turning it had no effect. I started looking at the board and it turns out that there is another, less visible trim pot (VR4) up near the MIDI jacks. I can't even find it in the schematics, but once you get it in range (12 o'clock in my case), VR2 starts being helpful.

If VR2 is too far clockwise, you get more of the aliased "zipper" sound and too far counter-clockwise you get a more hissy/breathy sound. I can't find a specified voltage nor a test point for calibration, but I found it easy enough to calibrate by ear.

I had to take the CZ completely apart for other repairs. The screen had missing rows, but almost any HD44780 based LCD works as a replacement. Some buttons were unresponsive, but contact cleaner made them operable.
While I had it disassembled I took some photos of the trimmer locations. They're on the main board appropriately marked "M4152-MAIN".
To be clear, you only need to remove the bottom of the case to adjust things. Casio was nice enough to provide some holes so you can access the trimmers from the underside of the board.

5 comments:

  1. Thank you SO MUCH for this article ! I have the same issue on my CZ 1000 and hope this will help me to repair it.
    The Internet has been invented for people like you, I bet :)

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    1. Thank you and you're welcome! Best of luck with the repair.

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  2. Thanks for the great post.

    A few notes : I think you got lucky finding the sweet spot for VR4 by ear. I did eventually, but it took a considerable amount of trial & error. Regularly cycling the power was also important -- sometimes the adjustments of VR2 & VR4 didn't seem to take hold until after power cycling. And while Casio did make it convenient to adjust the trimpots without removing the PCB's, after 45 minutes of trial & error to find the proper spot for VR4, I flipped over the PCB and saw that the sweet-spot for VR4 had been marked on the top of the trimpot with a bit of paint by Casio all along - doh!

    Lastly, I would consider adjusting the title or metadata for this post as it took me a while to find it and barely did -- while technically it is a DAC adjustment, more accessibly worded I'd say this is a CZ "noise fix/repair". If your CZ is noisey, you may not think to look for "DAC adjustment".

    Still very happy with the results and your article was very very helpful! Thanks again!

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    1. Well, I'm glad you found it!

      I took your advice and changed the post title. Hopefully more people will run across it.

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