Got an SVA2 the other day for free that was basically dead. It would light up when you gave it power but no display no audio. Ended up replacing the following:
Main power filter cap
Channel select and BW/Color mode switches
Doing the above and reseating all of the small 74 series logic ICs got it up and going with full play ability for one player games. However, the current issue and one that has been a constant issue since it first powered up, is that player 2's difficult selection is stuck in the novice setting. Both of the lights are usually constantly lit with each of the LEDs getting a bit brighter when you push the corresponding button to select the difficulty. But while the LEDs glow brighter when the button is pressed, it doesn't actually change the difficulty option at all. I've been using the colorbar generator and Space Invaders to test the switch usage.
Since the 74 series logic is all that I haven't replaced, I'm suspect that one of those is the culprit in some way?
It could also be an issue with a trace or traces that are broken on the PCB. Slight flexing on the PCB will cause the player 2 difficulty lights to flicker or come on and off but even then the actual difficulty never changes. I did reflow the LEDs to ensure they weren't loose and I've gone over the entire board carefully and can't see any cold solder joints.
Another very strange thing, is that the lights behaviors can also be changed by simply plugging and unplugging the RF cable on the main board...yeap... And in fact, I found that there is some correlation there because the RF signal is pretty snowy. But if I press and hold down on the Novice difficulty button, the picture would become crystal clear?! So yeah, the issue must stem from something with the 74x logic or some short between the difficulty selection circuit and the RF modulator?
I've not found schemes for the SVA2 so just putting this info out there for others to learn from or if they have any other ideas on where I should look, I'm all for it?