SNES MINI. RGB Amplifier Chip Mod or Standard 3 Wire Mod??

FireAza, I think you're confusing the N64 and 1CHIP guides. Both use 75ohm on the outputs:

http://www.retrorgb.com/n64rgb.html

http://www.retrorgb.com/snes1chip.html

 

No, I haven't taken measurements on a N64. It's hard to do without the test program for it.

Check your RGB cable, it might have the 75 ohm resistors and 220uf caps already in it. If it does, you do not need to add anything to the output lines. You should only have 1 75 ohm resistor and 1 220uF cap on each output line.

 

Also, I suggest following retrousb's guide he posted, and follow the instructions at the end with adding the 750 ohm resistors. This will adjust the RGB to the proper levels before going into the RGB amplifier.

 

Ahhh, that's right, I forgot he said he has a PAL RGB cable and an NTSC system. Good catch.

 

Well, it's a PAL cable, but modified for use with the Super Famicom and American SNES. I took out the resistors and added in 220uf capacitors on each color line. Okay, so since I already have the 220uf cap in my cable, I just need to add the 75ohm resistors as shown by retrorgb in his guide and and this cable will give correct output on both the SFC and NTSC N64?

Also, his guide says for the N64, to just stick the resistors on the input side of the amp, while his SNES guide says to solder them to ground in a particular location. This is the right way to do it then? I'm a total electronics newbie, but I can understand why soldering the resistors to the input of the amp would lower the strength of the signal. The signel comes from the board and goes though the resistor, lowering it's strength. But for the way retrorgb describes installing into the SNES, it looks to me like the signal would come out of the board, up the leg of the resistor then along the wire to the amp, totally avoiding the resistor. That's probably wrong, but I'm having trouble wrapping my head around how this setup lowers the strength of the signal before it reaches the amp. Seems to me like the simple way would be to just stick the resistors to the input side of the amp, but hey, I'm a designer, not an electrical engineer, so I'll just have to trust you guys

 

Yes, if you have the caps in the cable you just need the resistors on the output.

Stop looking at the N64 guide, it's a different type of mod. The 750 ohm resistors go between the solder points he shows and ground. The resistors are added to lower the signal coming out of the PPU. They are used, along with the resistors that are on the board next to those solder points, to convert the current coming out of the PPU to a voltage. Think of it as part of a digital to analog converter circuit. Originally, the original circuit produced too high of a voltage, hence the increase in brightness. Read the thread I linked, there's more information about it in there, but trust me, it will work properly.

 

Just to mention here:
At the moment I'm working on a new version for the SNES-Amplifier. My aim is to create a uniform design for PAL- and NTSC-systems by using a simple RGB-cable without any components within the RGB-lines (neither caps nor pull-down resistors). All components will be on the PCB. I've done a lot of measurements in my PAL-systems as well as in a US-mini of a friend of mine.
I came up with the conclusion that it should be possible to have a common network and just adjust some resistor values at the input side of the THS7314... Will keep you inform here; current state is that I've ordered my 'new' design

 

Cool, that means I can follow retrorgb's guide as is then!

Not even if I want to do the same mod on a N64? I'm planning to mod both a SFC and a N64, you might have gotten mixed up and thought I was only modding a SFC

 

The extra 750 ohm resistors won't work with the N64 mod. I'm just saying the 2 mods are a little different.

 

Sounds good! You can probably add both sets of 750 ohm and 1.1k ohm resistors and use a jumper to choose which set depending on the system.

 

Uh, I might be a bit confused here, but you're saying that performing this mod (http://retrorgb.com/n64rgbmod.html) and adding the 75ohm resistors as suggested doesn't work?

 

I really think you're confusing yourself...and you're confusing 750 Ohm and 75 Ohm. Just read the guides one at a time. Maybe these pics can help:

For the N64 mod, the amp should look like this with 75 Ohm (NOT 750 Ohm) on both the inputs and outputs (sorry for the really bad pic): http://www.retrorgb.com/images/THS7314-08.jpg
...a bit more of an explanation here: http://www.retrorgb.com/ths7314.html


To be honest, I'd leave your 1CHIP SNES alone. It looks great as-is and if you're not comfortable with these instructions, you can permanently damage your system. If you really want to try it, the amp should look like this: http://www.retrorgb.com/images/THS7314.jpg
...then add the 750 Ohm (NOT 75 Ohm) resistors to a different place as shown here: http://www.retrorgb.com/images/1CHIPBypass-11-largeDIY.jpg
Don't forget that when you do that mod, you have to lift the output pins on the S-RGB chip: http://www.retrorgb.com/images/1CHIPBypass-03.jpg

 

Ahhhh borti, you never cease to amaze me. You beat me to it! I was in the middle of laying out such a design and incorporating the pull down resistors on the THS7314 inputs to bring the signal levels down to spec, as described by Ultron in another post: https://www.assemblergames.com/forums/showthread.php?53053-SNES-Mini-RGB-Measurements.

Since you are further along may I offer some suggestions if you end up revising the board.

1) Incorporating through holes inline with the RGB and SYNC pads. This would give people the option of using low profile right angle headers instead of soldering directly to the pads. To illustrate here is a picture of my NESRGB board that I installed that incorporates such a design. I have outlined the pads with through holes in red. Using it would be completely optional but would yield a slightly cleaner install if one decided to use it.


The low profile right angle headers I was looking at would be the similar to the ones used in the 78xxSR Series switching voltage regulators. If you wanted to take a peek at the dimensions, its on page 8 http://power.murata.com/data/power/oki-78sr.pdf

(As an aside I use that regulator in place of the old 7805 in my SNES and AV Famicom so I can do away with the heatsink)


2) Have the ability to go from SNES amplifier board pads straight to the multi-out pins 1,2,3,4, and 9

The NESRGB mod requires soldering to the RGB and SYNC pins on the multi-out connnector but there is no need for resistors or amplifier IC's. Rather than soldering to the multi-out pins directly, I envisioned a cleaner install by using the SNES amplifier board naked without any components and being able to create a direct connection from the board pads to the multi-out pins by applying a blob of solder to some jumper pads to create the direct connection.

Perhaps this is more ambitious depending on how you are laying out your board, but its something I was incorporating into my design. Although one might argue that such a simple thing might be better realized in a totally separate board, it would be nice to have a unified board

EDIT: Updated with the correct Murata link and page #

 

Ah yes, that's where I'm getting mixed up. I'm mostly looking to do this mod to remove the line down the center of the screen. It's not that noticeable, but it would be nice to be rid of it.

 

With this thread getting busy again and people talking about their new designs it seems like a good time to post some pics of my PCB for the SNES mini/SFJr. Sorry for any blurry pics.









It's pretty much a restoration of the parts that Nintendo omitted from the SNES mini/SFJr based off the RGB, S-video and C-Sync circuits of the 1CHIP Super Famicom.

For all intent and purposes it's not really any better than the basic 3 resistor RGB mod apart from the extra S-Video and C-Sync circuits, some ESD protection and EMI suppression components and also Ultron's resistor mod to restore the RGB signals to normal levels. I designed it from a purist point of view, not to improve on anything but to restore the parts that should have been there originally. With the exeption of Ultron's RGB resistor mod of course but it depends which way you look at it. After seeing the correct RGB signal levels in action now it makes me think that is how the game developers intended the games to look. The different shades of colors on the screen seem to blend together better to make a more natural looking image overall compared to the slightly washed out color tones of the original incorrect RGB signal levels.

The pics are of a test install so it's slightly unfinished. I seem to be having some teething problems with the installation at the moment. I designed it so that the pads that connect to the pins of the S-RGB chip go all the way to the edges of the board but for some reason the PCB fab decided to move them back 10mill to match inline with the GND pour and the 10mil of solder mask is making it very difficult to make the solder bridge between the pads and the S-RGB chip pins.

I have managed to test it though and for better or for worse it works exactly like my 1CHIP Super famicom, interference noise and all

 

Seriously impressive. About a week after I put a THS7314 in my own machine too... lol

 

Waow. So tiny and optimized! I love that kind of work!

 

Thanks for the compliments guys.

It's a bit of a bitch to install though

 

kel,

This is pretty ingenious method you've come up with. I've been thinking a lot about how to tap into the S-RGB IC in a clean fashion.

I came across SMD DIP sockets. My initial thought was I could remove the IC and put it on a through hole jumper board where I would then have access to all the pins. Unfortunately it seems they don't make them with pins of the correct pitch.



Did you get your fab house issues resolved? I would be interested in seeing what measurements one needs to get a PCB precisely lined up to the edge of the IC to get good bridge if you are willing to share. It seems as if the heatsink would get in the way though. Or do you remove it and replace the 7805 with a switching regulator?

 

Thanks, I'm glad you like it.

My initial idea was to use castellated vias instead of pads which would ensure that the copper would reach to the edge and also be on the sides of the board but I scrapped that because I was worried that the part of the via on the bottom of the board would be too close for comfort to the adjacent pins/pads of the S-RGB.

Nice idea about the SMD DIP sockets. I thought of a similar idea using though hole DIP sockets with the pins soldered to the sides of the S-RGB pins and the socket resting on top of the S-RGB chip. This way you wouldn't need to remove the S-RGB chip which would save a lot of people destroying pads accidentally whilst trying to remove it. I can't remember why I didn't didn't go that route in the end, probably to keep the design as simple as possible. In hindsight it seems like it would be a lot easier to install than the way that I went for, depending on whether or not a suitable DIP socket with the same width and pitch as the S-RGB chip can be found easily.

I never got back to the fab house regarding the pads not reaching to the edge of the board. This order was like a cross your fingers and hope for the best thing for me. I didn't factor price when designing the board as it is my first attempt at designing a PCB and I had no way of knowing how much it would cost. Unfortunately because of the 5 different boards in one design and the half holes it worked out way too expensive in small quantities so I doubt that I would be making another order anyway, I just can't see the demand.

At this point I'm stuck with trying to find a way around the problem. I'm thinking of trying some solder paste from a syringe to make the bridges easily but this still all makes for a complicated install which is what I was trying to avoid.

The heatsink still fits in place. Part of the design was to raise the heatsink by the same amount as the board thickness (0.6mm) so that the SMD components on the board would pass under the heatsink safely with about 1mm clearance. That's the purpose of the weird flag shaped parts with the large hole in the middle for the heatsink screws.

I have attached the eagle lbr file that I made for the pads around the S-RGB from my design. It just needs a board outline running flush along the inside of the pads with enough space at the far ends for the overhang at the each end of the IC. It is not a tight fit, as you can see in the install pic that I posted there is a slight gap maybe a few mil or more between the S-RGB pins and the board outline but I didn't want to chance making it too tight of a fit just incase it it didn't fit at all. I could imagine that if the fab house would have made the pads reach the edge of the board like it was supposed to be instead of 10mil away then the the slight gap between the edge of the board and the S-RGB pins wouldn't have been such an issue but who knows.

There's no point in me revising it unless I decided to order some more so sorry but the measurements in that lbr file are the closest I have at the moment.