Castle VCO Help

Hey ya’ll! I have a couple Cadet VCO RevE boards that are exhibiting the same issue. I have linked a video to illustrate my issue and a couple photos showing the build itself. Anyone who is willing to lend an extra set of eyes would be greatly appreciated.

Cadet VCO Video Link

Hi Kharmasabits,
The first three images in your post are the same angle repeated - is that what you meant to post? Could you please upload a solder-side photo if available?
Some of the Castle (not Cadet) VCO behaviour in the video looks a bit glitchy, but the only thing that looks actually wrong to me are the parts of your video where the VCO oscillation is black on the left side of the screen and only starts on the right side. I’m not exactly sure what might be causing that…
Could you please describe any behaviour that isn’t as you expect, if it’s something else?
Caveat: I don’t have a Castle VCO right now so my ability to help is a bit limited. But I’m confident @pbalj will follow up pretty soon with much better informed advice :slight_smile:

Hi aladan, thanks for your reply. Each image is simply a different depth of field making each chip legible. I forgot to mention I originally built this module using the RevD BOM and schematic. I have recently changed out the 1N5711 diodes to the 1N4148. I was expecting the functionality to be similar to that of Prismatic Ray or Cadet IX. In the video I go through several functionality tests. When synced horizontally the square wave stays right justified and only allows limited scaling of the lines. When the board is synced vertical the lines seem fragmented and unstable. In this case the scaling is also extremely limiting. Later in the video I add some VC using both horizontal and vertical ramps. Unfortunately, I don’t have an oscilloscope for testing any of my equipment and my technical vocabulary is almost nonexistent. I’ve never seen one of these modules being used directly so I’m not sure what to expect. I have built many of these and all work great with the exception of these two. I’m sure I am missing something.

Good questions, and I’ll try to help where I can. In vertical sync mode I know what you mean about the “instability” - it’s particularly noticeable with the castle VCO because it’s a square wave, but I think if you look closely you’ll see the cadet VCO does the same thing - the issue is that even though the start of the waveform is synchronised with the start of the frame (i.e. the top of the picture) there’s still a tiny, tiny bit of variance in the frequency of the oscillation which means the start point of an “on” section varies slightly within each successive frame. It’s less noticeable with the cadet VCO because it’s a triangle wave and doesn’t have such a sharp transition from “off” to “on” as it happens. Also, the castle VCO goes to a higher frequency (i.e. closer lines) so maybe the effect is more marked.

The right justification of the lines and the VC scaling issues I can’t explain at all, sorry - I think that’s one for Phil. It would be worth checking all your component values to make sure a 100K hasn’t slipped in where a 1K should be or something like that, I guess. Even desoldering one pin of each component one by one and measuring them out of circuit, if you have a suitable multimeter. But that’s a lot of work so check them visually first.

Look particularly at C11, R13, R14, R15, D5 - they’re part of the sync circuit. A wrong C11/R13/R14 might cause the sync to stretch and the oscillations to start late, or something like that? But I’m just guessing.

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Thanks for pointing that out! I think I swapped R15 and R21. I will update this as soon as I get them swapped out. Thank you for helping me out. Just got to the point where I couldn’t stare at it any longer… Ha!

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These are not quite the same as the symptoms on my Castle VCOs but I do have some fuzziness / sync glitching like I think I’m seeing in your video. I had a conversation with Phil on Discord a while ago where he recommended replacing R14 with 47k and C11 with 10nF for sync issues:

I have still not got around to doing this actually (it’s been 3 months?! :grimacing:)

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