So, I populated one of borti4938's RBG bypass boards reputed to give the correct colour values (this one https://oshpark.com/shared_projects/0v1eZKgw), and installed it into my SNES mini. It works perfectly for the most part, but there are a few issues with it, related to sync. So according to the github instructions, it says to use anywhere between a 421R and 75R resistor on the sync line. However, there is no such thing as a 421R resistor, the closest I could find was a 422R one, but there is a 421kR resistor. Anyway, I have found that using the sync from the bypass board at these values produces some very strange colour errors, like red banding across the screen intermittently, and I have tried both 422R and 75R, and they effectively produce the same results. The only fix I have come up with is to use the sync from the built in RGB chip, and just wired it to pin 3 of the multi out as you would with the first revision of the RGB bypass. Any ideas about what's happening?
@borti4938 a far shot: Could it be from slightly different timing on the RGB clamps? It's got be clamped somewhere, right?
Why not try something inbetween 75 and 422? Like, 330 Ohm? If you dont have an 0805 package of that value, then use a standard resistor, just to see if it works and then replace it with a smd one later.
Even with 1% resistors, 422 is plenty close enough, as theres a variation of 4.2 ohms allowed anyway.
That's what I figured, but it doesn't tell me why the sync from the bypass board produces some funky colours.
It's quite difficult to see where your problem is without any pictures. Assuming your installation is correct: - your TV might not like the 75ohm terminated /CS (unlikely), you may try to replace the 75ohm resistor on the bypass board by 0 ohm, i.e. a simple short (as well as the 330uF capacitor on top). If this does not help, just post a few pictures of your installation.
Sure thing, I'll try bridging the connection this evening when I get home. In the mean time, here is my installation: Hope that helps.
So I tried just bridging the gap with a blob of solder and not using a resistor at all, and guess what? It worked! No more strange red banding. For the record, I'm using it on a Framemeister rather than into a TV directly.
Did you have the problem also with connecting the Mini directly to the TV, or was it just with the Framemeister in between? I don't own a Framemeister, but iirc one can set up the sync level of the input in the Framemeisters menu...
I never connected the Mini directly to the TV, only to the Framemeister. Yes you can adjust the sync signal with the Framemeister, but it needs a decent signal to begin with, and no amount of adjusting got rid of the red banding.
