Connecting cables to output for better image, Sony PVM 20-L5

[BoredNerd]

My test setup: Sony PVM 20-L5, SCART->BNC cable from retrogamingcable.co.uk, PAL Mega Drive 1 (NTSC modded) and noname SCART cable, PAL SNES and noname SCART cable, PAL Wii with noname component cable and RCA->BNC adapters
My problem: Any console I tried produces dark image(same like on my LCD if I set backlight to bare minimum) both in NTSC and PAL even after calibration (used Artemio's 240p Test Suite). By accident, I discovered that if I put RCA->BNC adapters on output, image looks very good. Also, I get the same quality image if I plug-in my cables to output. As far as I understand RCA->BNC adapters removes automatic termination which results in brighter image. Does it mean that my PVM is just worn out and will die soon? Any chances that this problem caused by bad cables?

Thanks,