I have been working to maximize Ramixx500 V2’s analogue RGB video output and interestingly I have found few improvement points that are essential:

• Pin 15 of CN9 so-called _CCK requires 47Ω termination (normally provided by genlock if plugged)
• Alternatively, the following pin can be lifted (disconnected / desoldered) from the motherboard to disable the buffered _CCK line:
  • Ramixx500 V2 pin 6 of U41
  • A500 Rev. 6, 8A1 (PAL) pin 6 of U41
  • A600 Rev. 1.5, 2 (PAL) pin 11 of U32
  • A1200 Rev. 1D.1, 2B (PAL) pin 4 of U32
• Each colour line benefits of a L-R bead insertion as bead cuts high-frequency noise.
• A high standard VGA cable increase the noise immunity.
• A decent grounding of the motherboard.

In the Amiga environment the jail bars are probably generated by peak noise induced by a floating _CCK (clock out for the genlock) and empathised by bad quality shielding/grounding at cable ends, regardless the resolution or de-/interlaced PAL/NTSC video modes.

Tested with:

• Amiga Test Kit v1.18
• EA Deluxe Paint III and 4.5 AGA
• BenQ LCD Monitor G2420HD (ET-0027-B) October 2009 Rev. 00-132-BA [VGA]
• UGREEN ‎11614 VGA Extension Cable [length 6 ft / 183 cm]
• Sony Trinitron CRT Monitor PVM-9045Q [RGB + SYNC]
• RS 790-2805 Straight 75Ω RF Adapter BNC Plug to RCA Sockets [250MHz]
• Mediabridge 70-040-06B Component Video Cable [length 6 ft / 183 cm]

(schematic from amigawiki)