Diy Coaxial (digital) Output Gives Interference On Video? Options

[dennisv9]

i soldered some connections onto my xbox (see post 'Quick Guide For High Def Output, Add High Def without the M$ Pack'); i added all switches (3). just added scart, svhs, coaxial, toslink etc. etc. as far as i can test, it works quite oke (although i mixed op luminance and chroma on the svhs resulting in a non/bad working svhs in first instance i got most working. unfortunately i have no SOG monitor; so only green output on my vga). scart is working; stereo sound is working etc. etc. but when i connect a cable (a physical cable!!) to the coaxial (digital) output; i get interference on video (scart, composite and svhs). i get 'striping' / 'rolling' picture. as soon as i take out the cable out of the coaxial connector; it works fine. rather nice/good picture.

so the coax is interfering with video somehow. i checked my soldering jobs; i do not seem to have any short on the AVIP connector (i soldered the wires directly onto the avip pins underneath the motherboard). for all the dataconnections (e.g. audio, video etc. etc.) i used ONE common ground (i just ran all ground wires to a screwhole. without grounding i get bad / rolling picture; as soon as i ground the wires to any ground (i use the screwholes) i get nice picture. the coax ground connection is one 'loose' wire; meaning it is not bundled with all the other ground wires. so i tried grounding the coax at different ground points. no luck, as soon as i connect any cable to a grounded coax output, it runs interference. any help; insight or tips?

are there any tests i can run?