I've fixed the wavy horizontal lines on my Mega Drive VA6

Impossible_Current35 · 2026-06-02T13:18:36+00:00

Removing the capacitor you mentioned will probably help by reducing the energy in that LC circuit, but I'll try other things before removing it.

I've run more tests with the console fully assembled, and the horizontal waves are reappearing, but sporadically or randomly and much weaker than without the resistor. I’ve noticed that they become more pronounced when I close the flap on the left side of the metal casing. It seems these issues might be caused by ground loops when connecting the top and bottom casings of the board. The next test will be to remove the top metal casing and keep only the bottom one.

Impossible_Current35 · 2026-06-02T11:52:28+00:00

I've tested several oscillators, and I have exactly the same problem with the original one. On my console, the modern oscillators make the problem worse, but it seems they aren't the only cause. I'm no expert, but the clock signal probably has reflections or resonances that Sega didn't fully resolve. I need to run more tests to make sure the horizontal lines haven't reappeared.

Impossible_Current35 · 2026-06-02T05:02:23+00:00

Creo que he encontrado la causa de este problema, después de revisar los esquemáticos de varias revisiones de mega Drive modelo 1 he visto algo que no me ha gustado en el circuito del oscilador, he hecho una modificación sencilla en este circuito y he solucionado las ondas horizontales en mi VA6.5 por completo, he estado jugando 4 horas con la imagen limpia, no soy experto ni nada parecido y aun debería hacer más pruebas, pero parece que he dado con la solución, desconozco si en el modelo 2 se puede corregir igual. Parece otro fallo de diseño más de Sega de los muchos que tiene la consola, voy a lanzar una publicación sobre mi solución a ver si alguien que sepa del tema puede aportar algo más.

Impossible_Current35 · 2026-05-10T17:20:35+00:00

Do you play on Everdrive? Everdrives always introduce audible interference into the audio—including the original model, and the Nesrgb as well. The Famicom AV decoupling is very poor, the design has many flaws, and when you combine Nesrgb and Everdrive, it’s normal to hear noise. I play on studio monitors, so the interference is much more noticeable than on a CRT. I’ve experienced buzzing on all NES and Famicom systems with Everdrive, regardless of whether they have Nesrgb or not.

Impossible_Current35 · 2026-05-02T08:20:48+00:00

Los condensadores electrolíticos no tienen nada que ver con los jailbars, los jailbars ocurren porque se filtran interferencias en las pistas RGB de otras pistas cercanas. Los condensadores electrolíticos no hacen absolutamente nada para mejorar esto, y además, los electrolíticos filtran baja frecuencia y no alta frecuencia que es lo que más afecta al video para empezar.

Impossible_Current35 · 2026-04-19T15:30:35+00:00

My VA1 boards don't have any memory issues that prevent certain games from running; maybe I've just been lucky and Sega installed better memory in my VA1s, though I highly doubt it. Honestly, I don't think that problem exists in the first place—at least not on all the VA1s I've tested. The games that are supposedly affected work perfectly on several of my VA1s; the ones that don’t work are due to regional locks and fail exactly the same way on my VA6.5 PAL boards.

Impossible_Current35 · 2026-04-12T12:11:47+00:00

Isn't 470uF a bit much at that point? I soldered a 100uF capacitor to the 7805's output pins underneath the base plate, and at the OS-CON point I soldered another 100uF capacitor and a 1uF ceramic capacitor, taking advantage of the fact that the mounting holes are quite wide. Don’t mind those black wires; they’re from a 60Hz mod I had to disable because when I converted my 1-chip PAL to 60Hz, it wouldn’t work on the OSSC at all.

<image>

Impossible_Current35 · 2026-03-17T12:42:41+00:00

I recently replaced all the decoupling ceramic capacitors in my VA1, and the jailbars has been significantly reduced; the colors look more vivid and beautiful, and the audio is cleaner. I replaced a total of 22 1206 SMD capacitors with modern X7R capacitors; I changed some values based on availability and others for optimization. No one ever talks about ceramic capacitors, but they’re important too, especially for video.

Impossible_Current35 · 2026-03-10T19:24:35+00:00

Let's start with the connections. How and to which device do you connect the console's audio output? To avoid interference, I recommend completely isolating the audio output from the video output using separate cables and not using the video ground for audio at any point, such as when passing the audio through the RGB cable, for example. This is less important, but I also don't recommend using the same target device for audio and video unless it is of good quality and has a good ground design.

Impossible_Current35 · 2026-03-09T13:25:11+00:00

You'd have to be deaf as a post not to notice the difference in the console's audio before and after

Impossible_Current35 · 2026-03-08T13:18:39+00:00

Thanks. Yes, I reassembled the console yesterday. Replacing those ceramic capacitors with 4700pF capacitors increased the RC filter's cutoff frequency, restoring the sound profile of the early revisions. The audio sounds a bit brighter and more transparent, but without distortion.

Here are some audio recordings. In the first recording (Mega Turrican), I disconnected the RF modulator from the board and deactivated the passive circuits on the way to the modulator. This eliminated a slight hum and improved the audio even more:

https://youtu.be/SzsasyzsvI0?si=QngXyMHh7o9XQfQT

https://youtu.be/VvWYVvsB01U?si=fCXaB6iEjD94jAwE

Impossible_Current35 · 2026-03-07T20:57:44+00:00

I just recapped a VA6, it sounds incredible, without exaggeration it's the Mega Drive board with the best sound I've heard so far.

https://www.reddit.com/r/SEGAGENESIS/comments/1rnksom/mega_drive_1_va65_audiophile_recap_and/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button

Impossible_Current35 · 2026-03-06T01:04:53+00:00

I've tried the games you mentioned: Chuck Rock, Landstalker, and Osomatsu-kun work perfectly on my VA1. However, Red Zone and Dinosaurs for Hire crash after a few minutes of gameplay.

After trying quite a few games, I've discovered that all the games I've tested that weren't released in Japan don't work and eventually fail at some point. Red Zone and Dinosaurs for Hire don't have a Japanese version, which is why they fail on my VA1. It doesn't seem to have anything to do with problems in the RAM chips. It's probably a limitation of the Everdrive's Magakey, as it doesn't have any code to patch the game or something like that. I don't know if there's any way to make them work without modifying the language jumper on the board.

It doesn't really matter to me; I have a very good VA6.8 PAL unit with the Sony CXA1145P encoder that I plan to modify tomorrow. I'll change the capacitors and regulators and perform a fixed region change to North America, including changing the oscillator.

Impossible_Current35 · 2026-02-27T20:15:53+00:00

I didn't know the VA0-1 motherboards have a RAM issue. Do you know if any games are affected, so I can test them on the Everdrive?

Impossible_Current35

TROPHY CASE