Cadet II RGB encoder ground question

I’ve just finished building a DIY Cadet II RGB encoder, and my build doesn’t currently work correctly. I have a V1.1 board that I bought a week ago. I started checking voltages, and found the +5V output from the 7805 was no good (~1.2V). Then I traced all my soldering, and found that the common (ground) pin on the 7805 wasn’t connected to ground on the euro power connector. I couldn’t see any issue with my soldering, so I referred to the (hi-res) photos I took of the board before soldering it, and I can’t find any connection between the euro power connector ground (pins 3 through 8) and the main ground net on the board! Is this expected?

I looked at the schematic and the +5V regulation section is a bit different to what I’m used to seeing - the 7805 has some small capacitors next to it (presumably internal to the 7805 part and just there for information?) and a little ground icon connected to the pins common to those two little capacitors, which looks like it is then connected to the main ground plane.

P.S. I wasn’t using patch leads for my testing, just bare wires. Maybe it works for other people because when they patch RGB signals in via the panel jacks there is a path to supply ground via that patch lead? On the PCB that I have the euro power connector’s ground pins only connect to C2 and C6 (as per the schematic).

There are a lot of things that connect to ground in that module, so I’d be very surprised if the only things connected to ground on your PCB are C2 and C6. Typically, ground is a whole plane (often the back of the board), and the ground plane connections are very easy to miss when looking at the board because they’re little connections from the filled plane to the pads.

Interestingly, in the schematic, it looks like the eurorack power header ground isn’t connected to the ground net the way it is in the other Cadet schematics. I’m not sure what EDA software LZX uses, so it might connect to that net in some way that’s not on the schematic.

It looks like the sync header’s ground connects to the ground net, so maybe that’s the ground connection on this module? Do you have the Cadet II plugged into a Cadet I via the sync headers? It needs to be in order to work since the Cadet II needs the sync. (And maybe it needs the ground too, I guess?)

Rather than a cadet 1 I am using a DIY sync generator that I designed and built on veroboard, using an LM1881 for csync and a CD4538 for blanking. That board worked fine with my DIY veroboard layout of the cadet 2 circuit (until the AD724 overheated and failed since I had failed to include the power pin caps.)

I tested various other grounded component legs on the cadet 2 and they’re all connected to the ground plane just fine. It sounds like your interpretation of the schematic is the same as mine, and the euro connector and C2/C6 might indeed be missing a connection to the ground plane on the PCB though.

Looks like you’re correct! C2/C6 and the EuroRack connector are missing a GND connection on the C2 PCB. And Joe is totally on the ball here with his theories. This is a bit of a nonissue in terms of correct operation for most, because you’re always going to be using this module with the 14-pin sync ribbon, and will receive system power and sync ground through the power ribbon and sync ribbon on those modules (which is explains why we never noticed this.) Still bad practice though of course, because you want those return ground connections going back through the ribbon with the power connections. Here’s an easy wire lead kludge for your C2:

I’ll make sure we clean this up in the next revision.


THANKS!! This was driving me insane. I don’t always use a full sync ribbon, and I couldn’t figure out why it wasn’t working sometimes. Hallelujah!


Update, it works. I’m a little embarrassed that I didn’t figure this out myself. It takes a village!


I built the Cadet II and made this extra grounding connection. Is it normal that I get no picture from it, being that I have no Cadet I yet and no ribbon cable attached? I tried connecting a fixed voltage and an output from Prismatic Ray to the inputs and expected at least some image on my tv, albeit not synced, but maybe my understanding of the module and video synthesis is lacking. Total noob here :-).

@GijsvO without sync information the encoder chip (AD724) won’t be able to generate a useful video signal. It needs those signals in order to know when to generate the colour burst (and no doubt a whole host of other things relating to encoding).

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Thank you! So there is hope that I didn’t f-up the build :slightly_smiling_face:

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you can always post a picture of the top and bottom of the pcb here to troubleshoot!
but first test it with a sync generator

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It’s working perfectly now that I have the sync generator providing the sync over the ribbon cable. Hooray!


could a symptom of not doing the kludge yet be that the image is intermittently shakey? We are talking light vertical jitter that seems to be intermittent and does clean up when I plug it into different outlet’s surge protectors and bare outlets. But then it will return. I guess it does seem related to power. Like it started happening once when my air conditioning kicked in. Could have been coincidental. But then I turned the AC off, power cycled everything and it was fine again. When the issue is not happening it works perfectly. Haven’t done much testing. It is the v1.1 board. I did just get the Cadet I Sync Generator back from having the chip programmed by LZX (also older version from 8/19). I reflowed most of the connections on both boards (I and II) to make sure it wasn’t a soldering issue. Could it be a faulty component on either module? I am driving sync from a Sony DVD Player.

I guess my question is, could this missing connection cause any symptoms if using the ribbon cable to sync between modules? Or should I look elsewhere for the culprit?

The problem described in this thread only happens for people who are using the encoder module without connecting it to a sync gen using a proper ribbon cable AND not using at least one properly grounded euro cable, so it’s really unlikely to affect many people at all. If you use a ribbon cable or a normal euro patch cable then it provides a path to ground for the module, so I doubt this is the problem you’re seeing.

I think more likely what you describe might be caused by a poorly stabilised composite source? I see a shaky image when I connect my sync gen directly to a manky old VCR. Sometimes it’s not too bad, other times it is. Turning it off and on again often helps, but the best solution I’ve found is to use a frame synchronizer/time base corrector to generate a better source for the sync gen to lock on to.

For reference, I am using PAL. The NTSC experience may well be different.

Thanks so much, I appreciate you clearing this up for me. I will keep testing with the sync generator as the sync source and see if I have any further issues. The DVD player isn’t too old, but is very cheap and could very well be generating less than stable information.