I'm having a heck of a time trying to figure out what's going on here. I have a bunch of SNES clones that no matter what I do to isolate the problem I just can't get rid of it. Basically, after taping RGB/Sync from them I get this awful noise on screen. And by noise I mean the systems play fine and the image is ok but there is this pattern that is always there. These clones have the common 3-chip TCT (or similar) chipset found in many old/new SNES clones such as the TRISTAR64, FC Twin, Retro Duo's, Gamestation, portables, look alike SNES minis among many many others. I have tried different ways to amp the signals, sync cleaners, proper shielded cables, shielding the signals individually, different converters, etc.. with very little success. It almost feels like there is something happening inside the chip that produces RGB because the noise always comes in different ways. Checkered pattern: Even thou there is always noise sometimes it shows in a checkered pattern Diagonal pattern: Other times comes out with a diagonal pattern After many hours of testing I found that all of these clones have the same issue. Apparently some original SNES/SFC unit have it as well (specially those official units made in China) : http://vaot.mydns.jp/fc/sfcdiff.htm I'm guessing the cloned chips are nearly perfect that even the noise was cloned as well To make matters worse the RGB seems to be already buffered inside the chip. Any ideas as to what to do that may help?
Regular diagonal patterns usually hint at a clock line that gets into any of the analog video signals. If you have an oscilloscope, you can try to find it. If not, the usual method to fix this is a lot of bypass capacitors of various sizes and very low ESR
That does seems like it may be the case. Unfortunately I don't have a scope. Do you mean bypass caps for the RGB outputs? Thanks for your reply.
Yes to no available . The noise is coming out of the chipset way before it reaches any video encoder.
Since I've never seen an official SNES with this particular 3 chip layout I'm assuming the chip makers reverse engineered and packed mostly everything onto them. This is how the RGB and Clocking works. One chip (CPU/SOUND??? ) is drived by two xtals. One is a 24.576Mhz xtal (red marked pins Audio??? ) and the common 21.4772Mhz for Master Clock I suppose (yellow marked pins) RGB/SCIN and SYNC are tapped from a total different chip shown in the pic: R,G,B, SYNC (yellow pin), SCIN (pink pin) and the orange pin switches between 50 and 60Hz As seen in the pic below, RGB is always pulled down with a 1K resistor and coupled with a 1uf ceramic cap before reaching the video encoders. I also keep finding tons of threads about original SNES/SFC units with this terrible issue ( with the APU-01 being the worst) and some possible fixes but nothing that helps these poor clones https://krikzz.com/forum/index.php?topic=1370.0 http://shmups.system11.org/viewtopic.php?f=6&t=41943
With a scope it could probably be tracked down quickly but to state the obvious they're not exactly inexpensive and learning to use one has a bit of a learning curve.
