SNES-Mini RGB Measurements

Aside from the extra buffer from the THS7374 the THS7314 and THS7374 are almost the same. However, on the board I use a different voltage divider for red compared to green and blue. You can see in the measurements that red has a lower Vpp coming out of the S-CPUN than green and blue. The simple correction with the 1.1k resistor at every R,G,B wire to ground (parallel to the existent ones) won't change that.
What you can observe is that the color feels a bit different if you compare both methods.

 

Would you be willing to draw up a quick diagram of the parts necessary for use with an NTSC SCART cable? I read the readme but am still very confused as to which component is supposed to go where.

EDIT: Never mind, just learned what an Eagle schematic was. Sorry, this is basically the first time I've touched PCB stuff.

Well, I don't currently have any issues I'm trying to fix; I just want to make sure I get the best/newest version of the mod done.

 

I've updated the bottom silkscreen as well as the components naming in the schematic with their values. Now it should be more clear which component goes where

 

Ah, that's very clear now, thanks!

Also, one more thing I was curious about: will using your THS7314 board in a 1CHIP-01 unit improve the picture quality or is it primarily for SNES'es that have the vertical line issue? I've seen a few forum posts that the brightness of a stock 1CHIP unit is too high by default, though I was unsure whether this was actually due to an off-spec signal or people simply preferring a darker signal to aid CRT sharpness.

 

It will slightly improve the picture quality.
The brightness issue comes from the off-spec signal. However, my latest bypass boards corrects it.
The vertical line issue comes from the DRAM refresh impulse. In 3Chip-models, this refresh impulse can be deactivated by lifting pin 49 at the S-CPU (and set it to Vcc). I neither know side effects nor
the corresponding pin at the S-CPUN in 1Chip-models. However, the RGB bypass seems to help getting rid of the vertical line.

 

If you want to keep the stock encoder, will the old THS7314 fix of tying the lines to ground with 750 Ohm resistors fix the issue as well?

 

I've ordered your 1CHIP-03/SNES Mini board from OSH Park, and all of the parts from the list on Github. Can't wait to assemble this and solder that bad boy in.

 

And I've now populated the board and soldered it in to my Mini. I love it, it works great, the only thing that doesn't work is the sync line, it causes all sorts of problems like picture shaking and colours dropping out randomly. I've taken to wiring up the stock sync from the Mini's video chip and it works a treat. Tried different resistor values on the sync line and it seems to get worse with lower resistance.

 

I just realized I never updated the 3-wire mod page on my site with the brightness resistors...and it's been so long since we all worked on it, I'm completely drawing a blank on what needed to be done with that mod. I found the following post and it looks like all I'd need to do is add three 133Ohm resistors from the video line to ground: http://assemblergames.com/l/threads/snes-mini-rgb-measurements.53053/page-2#post-768707

Am I reading that correctly? Basically this, but the yellow lines would be the 133 Ohm resistors:

 

The 3 wire mod is wrong. The other mod you have on your page is the right one. The correction to the circuit needs to be done before the RGB chip.

 

Thanks for the reply! So, first do the basic 3-wire / 75 Ohm resistor mod, then remove R6, R7 & R8 (bottom of the board near the cartridge pins) and replace them with 133 ohm? Do you happen to have a DigiKey link to the right ones?

Sorry to keep bugging you, but I've been using the pre-made chips for so long now that I just forgot all about this.

 

No worries!

Keep the R6, 7, and 8. Wire up 3 1.2k resistors (Digikey does not have 1.2k 1% tolerance, but Mouser does - Link) from the vias to GND.



Connect the 3 RGB outputs from the S-RGB chip to the Multi-Out. Also connect C-Sync as well. Make sure you have a combination of 75 ohm and 220uF resistors on the output lines of the S-RGB chip, either in the cable or soldered on the board.

 

Oohhhh....this is all making sense now. It's the exact same procedure as when using the THS7314, since it's essentially doing the same thing (changing the brightness before it hits the amp). I'd just post this exact same thing in the guide, but without the blue wires, right?: http://www.retrorgb.com/snesminirgb.html#brightness

 

Okay, that was it, thanks for your help.

I just finished taking a ton of screen captures. I'll eventually try and get an many SNES revisions as possible, but here's what I have so far, including many different SNES Mini mods and a txt file with a full description of each. These are untouched bmp's without a watermark, so please be respectful and not use them without giving credit. I've had most of my pics stolen and used in other sites, eBay auctions, etc...it's quite annoying: http://www.retrorgb.com/files/SNESVersionCompareJune2016.zip

I bet the reason I used to think modded Mini's were better then 1CHIP's is because of brightness and both look identical with the THS7374 mod. I'd like to try taking a stock 1CHIP and adding the 750 Ohm resistors to it and see if it's as good as a 3-wire Mini with the 1.2k resistors. Thoughts?