RGB Encoder issue

I have build another Cadet system.

When testing the modules, it became clear that the sync cable was manufactured wrong.
All pins are shorted together.

I tested the RGB Encoder with another cable first, it worked correctly.

Then I used the sync cable to test some other modules. This did not work because the cable was shorted.

Now, the Encoder is behaving weird:

If I plug a VCO in the R/G/B channel, I see black & white bars with interference over them.
When I adjust the VCO frequency (sweep it up and down), the color comes in. It seems like the sync signal needs a nudge to work.
The PAL / NTSC switch has the effect that when switch to NTSC and back to PAL, the B&W effect appears again. This can also be resolved when adjusting the frequency of the VCO.

My question is: can a shorted out cable damage the RGB encoder?

And: how do I fix this problem? (I’ve also contacted LZX & Thonk about this issue)

I have another RGB Encoder that I build years ago that works perfectly.
So I cross-checked all the parts and solderpoints. no visible issues there so far.

I actually have this issue with the green channel on one I built earlier this year. Haven’t exactly been able to solve it either. Didn’t do anything different than on previous builds, so the questions do linger…