Hi all
I had an NESRGB (v4) installed in my Sharp Twin Famicom by a modder late last year. When it came back, the RGB picture had faint horizontal bands that pulse in time with the game music. They're most obvious on flat colours (the sky in SMB 1-1 is a good example), and they show up on both my RetroTink 4K and a CRT.
At first the audio was carried through the same DIN socket as the video (PC Engine-style pinout), so we assumed it was audio crosstalk. I'd already tried the correct 7.6V power supply and a few others, so I sent it back. Earlier this year the modder rewired it to the Neo Geo pinout, with the audio taken from the Twin's own audio output to a separate 3.5mm jack, and I bought a Retro Gaming Cables Neo Geo AES stereo SCART to match. The bands were still there.
So I've opened it up myself. The RGB comes out through the Twin's original rear RF-converter socket, with sync from CS#. Here's what I've checked:
- With the audio lead unplugged, the bands are still there
- The console's original composite output, with the NESRGB switched off, is completely clean
- The old tracks to the rear socket have been cut properly: no continuity from either RCA socket to any socket pin
- Adding a ground wire from the NESRGB straight to the socket's mounting lug made no difference
- Moving the RGB wires around made no difference
- Adding an extra ground path to the TV with an RCA lead made no difference
So the music is getting into the RGB somewhere inside the console, but I've run out of things I can test with a multimeter. Has anyone seen this on an NESRGB install, Twin or otherwise? I'm considering recapping the power/AV board or getting it scoped, but I'd love to hear if there's a known fix.
YouTube video of the issue here: https://youtube.com/shorts/oGwUGTMHy6Q?is=u_gOq7Cnl5FHGZSi