Newborn RGB Enocoder goes kaput

I just built two cadet modules. The Sync Gen and the RGB Encoder.
I switched them on and at first I got a green screen without any inputs, I threw some eurorack oscillators into the encoder and got horizontal lines and some really cool looking glitch effects, but when I unplugged one of the oscillators the video cut out, then the systems power reset, and now i don’t get any video at all from the encoder. I can still pass video through the sync gen from my camera, so I think it is still functioning well. I rechecked all my soldering and made sure all the connections were good, but I still am not getting anything, though when i have the RCA connector barely in on the encoder my display flickers the "no input sign.
any knowledge would be most appreciated.

That not how it’s supposed to work. If you don’t have anything input to the Cadet 2 it should result in a black screen. So it sounds like something was wrong from the very beginning, unfortunately.

The video output on the Cadet 1 is almost straight from the input (it just touches a few resistors and one of the opamps - check the schematic to see what I mean), so the fact that it passes the input to the output just means that one part of the Cadet 1 is OK, not that the whole thing is.

I’m a little unclear about exactly how it’s not working for you right now. Since your monitor seems to tell you when there’s not an input signal, does it say there’s input or not when you have it hooked up to the Cadet 2 output? If your monitor is registering a valid signal from the Cadet 2 output and it’s just all black, that’s a good sign that the Cadet 1 is sending the Cadet 2 a good sync signal. It should also mean that the Cadet 2 is handling the sync alright too (so much of the second page of the Cadet 2 schematic sounds like it’s working right). In that case, my best guess would be that there’s something wrong with the opamps (LM6172’s) in the Cadet 2 or their signal path.

If you’re not getting a valid (but all black) signal from the Cadet 2, that means there’s a lot of possible things that could be causing the issue.

It’s the later case. When my cable is plugged into the Cadet 2 my monitor says “no input”.
Thanks for the analysis. I’m fairly new to DIY So it looks like I’ll be looking for someone whom I can pay to take a look at these. Any recommendations?

you can also post pictures here , of the front and back of the PCB.
it is always better if you fix your mistakes yourself. keeps the DIY spirit high!

Good Idea! Thank you!

Well, nothing’s jumping out at me as obviously the problem (maybe someone else can spot something?). Might just be the angle and a trick of the light with the C1, but…

  • The pins on U3 look like they might be touching? (Also they look like kind of long.)
  • A lot of the pins on the components and headers look questionably soldered. I’d reflow a lot of those.
  • It looks like there’s solder splattered on various parts of the board… If that’s so, I’d clean those bits up, since there’s a chance they’re bridging things they shouldn’t be. Just touch them with a clean tip of an iron and it should pick them right up.

And as to the C2, the soldering doesn’t look as questionable in that pic, but there looks like there might be a lot of solder splatter there, too.

The photos of the solder side are not quite in focus but it seems like especially the front half of the board has some cold joints.
The solder needs to wet both the pin and the pad all the way around the pin.
Try to reheat the worst offenders, making sure to get good contact between the iron and both the pad and pin, waiting to see that the solder flows properly around the pin (Should take around 3-5 seconds once the solder starts melting if you’re doing it right)

try to get these results:

reflow to make the solderjoints better
and snip off all long leads.

I can check for correct parts and orientations this weekend. (if you can wait :slight_smile:


The polarity looks correct for everything.

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So I fixed my crummy soldering and now I get a display on my analog monitor color happens sometimes, but it’s black and white most of the time.
when color does happen it’s very washed out, nothing like my vidiot.
Also my digital television only displays anything when I’m using the vidiot to modulate the encoder and even then only when receiving oscillation of certain frequencies and it still is not a pristine image.
lastly it appears as though the blue jack of the encoder receives a little less signal then the other two.

Thank you for all the advice so far!

Keep working through your assemblies fixing cold solder joints, cleaning up any splattered solder, and use a multimeter to check for shorts on pins you think might be touching each other. Did you install the crystals in the right spots? Do you have NTSC/PAL modes all set correctly on sync gen, encoder, and Vidiot? (Power off and on again after changing any settings.)