SNES Mini THS7314 RGB AMP Mod Issues

[Larrs888]

Hi guys,

I really hope some of the knowledgeable folks in this great community can help me out please. I have had my SNES Mini for a couple of years with a standard 3 wire RGB mod, I have also been using it with my XRGB Mini for around 18 months. I always had some minor noise/chequer-boarding on solid colours which seemed off since it is a SNES Mini console with supposedly the best RGB image of any SNES console (once modded). I decided recently that I have put up with this issue for long enough and wanted a cleaner image, not being too great with a soldering iron and lacking the free time I sent my console away to have the old mod removed and have the new THS7314 AMP PCB installed with C-Sync hooked up.

I received my console back and whilst the image is vastly improve with zero noticeable noise present I now have a new problem that was not present before. Many games now have issues at the bottom of the image or in the overscan area on the right side of the screen, worse still Mega Man X now has an ugly green bar at the bottom of the inventory screen. I never had these issue before but the modder says its normal for a SNES Mini/1CHIP SNES. I think I would have noticed these issues in the past 18 months, especially as the SNES is my most frequently used retro system next to my cvms. Equally I can't find any other reports of these issues on the net and many rave about the SNES Mini coupled with an RGB mod and XRGB Mini.

None of my other systems have this problem so my xrgb is fine, I have also tried different settings, different scart cables and power supplies to no avail. Strangely some games appear ok (Rockman X2, Street Fighter Zero 2, DKC2) at least during a brief test but others display a faint white bar at the bottom in different places or white glitches on the lower right of the screen. This is really distracting and annoying when playing these games now. I have tried the SNES Mini directly with a TV and the issue remains although it is not as bad, I presume this is due to a TVs low pass filter being applied (LCD UK TV with RGB SCART IN) as when I enable the "standard" picture setting on the XRGB which appies a low pass filter it hides the problem in most games (but causes other issues so not a fix).

Either the AMP/THS chip is faulty or my SNES is going bad, I wanted to get some more advice before responding to the modding service I used.

Please see the below screens for an idea and let me know if you have the same issue with an RGB capable snes mini and xrgb.

(All carts are original)
Intro of Chromo Trigger:

Mega Man X - The title screen has a white line at lower part of the screen:

Star Fox glitches on the right side of the screen (I turned the brightness up to highlight the issue more but its always there regardless and noticeable with the correct brightness level:

Zelda Into has a faint white line in the middle of the screen:

Ultimate Mortal Combat 3:

 

[MuppeT]

I didn't know that this amp was that much of an upgrade from the original 3 wire mod.
What you are describing might be an issue with a wrong/bad resistor being used on your initial mod. Hopefully the guys doing your amp upgrade didn't recycle them resistors.

 

[Larrs888]

Well I read it wasn't meant to be and wouldn't have bothered if it wasn't for the noise I was getting on the image with the original mod, it got even worse when I connected to a SCART switcher, all my other systems worked fine with it. Here are the before and after photos, sadly I don't have a photo of the top of the motherboard and the Nintendo S-RGB chip that had the old mod connected. I asked for the photos from the modder as they put a warranty seal over the screw holes on the console after the work is completed.

Before:



After:

 

[Pasky]

It's just normal 1chip overscan garbage. 1-Chip's have this issue in certain games.

 

[Larrs888]

It's just normal 1chip overscan garbage. 1-Chip's have this issue in certain games.

I have read about some glitches with certain games on 1-CHIP systems, Aladdin, Demon Crest and Ghost and Ghosts but never about overscan problems. I swear these issues were not present when using the 3 wire mod with sync on composite video into my XRGB Mini. I know some consoles have overscan issues, such as the Mega Drive but the SNES Mini seems to the console of choice for a SNES with the sharpest a cleanest image, I surprised this problem isn't more talked about.

 

[Pasky]

Because it's not a big deal? It's in the overscan area...

 

[Larrs888]

It's just really distracting when trying to play games that display the issue and as I said it wasn't present before which leads me to believe there is an issue and the flickering gets really bad in Star Fox. Pasky I hate to ask but I don't suppose you happen to have an RGB modded snes mini with an XRGB Setup to post come comparison photos for me please? Sorry to trouble you

 

[kuze]

It's just really distracting when trying to play games that display the issue and as I said it wasn't present before which leads me to believe there is an issue and the flickering gets really bad in Star Fox. Pasky I hate to ask but I don't suppose you happen to have an RGB modded snes mini with an XRGB Setup to post come comparison photos for me please? Sorry to trouble you

The flickering sounds like you may need to adjust the sync level using the OSD menu on your Framemeister.

It's normal to see garbage in the overscan area using an XRGB mini with some systems/games.

You can play with the picture/zoom settings on the XRGB if it bothers you.

 

[Xian Xi]

Just use zoom. The overscan area wasnt meant to be seen anyway.

 

[Larrs888]

Thats for all the comments guys, maybe the garbage off screen was present before but it certainly wasn't noticeable before I had the amp installed. I have reset my XRGB Mini settings and played with the sync level to no avail. If I switch the HDMI colour mode from RGB Limited to full it hides most of it, again I didn't need to before. Perhaps the mod is amplifying these issues not visible before when the Nintendo S-RGB chip was handling the video signal. I certainly never had a green line at the bottom in Mega Man X before the amp mod......

 

[Xian Xi]

Thats for all the comments guys, maybe the garbage off screen was present before but it certainly wasn't noticeable before I had the amp installed. I have reset my XRGB Mini settings and played with the sync level to no avail. If I switch the HDMI colour mode from RGB Limited to full it hides most of it, again I didn't need to before. Perhaps the mod is amplifying these issues not visible before when the Nintendo S-RGB chip was handling the video signal. I certainly never had a green line at the bottom in Mega Man X before the amp mod......

Maybe because you didn't have the Csync mod.

 

[Larrs888]

I'm not sure about the c-sync maybe I'll have another play around with the other scart cable I have or even test with a composite video lead. Mega Man X always has the green line, I can see it even in an emulator or on a you tube video I have found so that threw me off. I'll ask the guy on the channel if he has the same issues as he is testing with an RGB modded SNES Mini on his XRGB Mini. Either those off screen glitches were not there before or I'm losing my mind.......maybe it is the latter. Screw the SNES I should just play more Neo Geo

Thanks again all. Sorry to digress with non neo related stuff.

 

[Thebonuslevel]

I have an rgb modded famicom jr. I dont notice any artifacts on the screen. I also use a 5x scale profile that over scans the image. Are you using a profile for the mini? If not, try downloading the profiles from firebrand.

 

[ballzdeepx]

Sorry to necro this, but I've thought about doing this with a THS7314 spare I had laying around.

I don't have a fancy PCB so I'm guessing I'd just need to do the following?

Solder in some 1.2k resistors on the RGB pads near R1 & C1 and tie them to a ground glob
Solder some wire on the resistor legs for RGB and run those to the AMP (along with 5v and ground), and then use 75ohm resistors to each RGB point on the multiAV out
For CSync, I can't tell in these pics, but it looks like they fed it through to the other side where they presumably tapped off the SRGB chip on leg/pin 18?

Thanks

 

[Pasky]

Sorry to necro this, but I've thought about doing this with a THS7314 spare I had laying around.

I don't have a fancy PCB so I'm guessing I'd just need to do the following?

Solder in some 1.2k resistors on the RGB pads near R1 & C1 and tie them to a ground glob
Solder some wire on the resistor legs for RGB and run those to the AMP (along with 5v and ground), and then use 75ohm resistors to each RGB point on the multiAV out
For CSync, I can't tell in these pics, but it looks like they fed it through to the other side where they presumably tapped off the SRGB chip on leg/pin 18?

Thanks

IMO, the 1.2K's to ground are unnecessary. I've taken a E2S datapath card and oscilloscope to the RGB lines, they are not oversaturated when I took a look at them, infact pure whites were 252/252/252 (255+ would be over driven). You can skip them entirely.

You want RGB channels inline with 0.1uF caps on the inputs, put a 0.1uF bypass cap between 5V and GND on the amp and then 75 Ohm Resistors on the output inline of the RGB lines. If your RGB cable doesn't have 220uF capacitors you'll want to put one on each color channel inline on the outputs as well:

 

[ballzdeepx]

IMO, the 1.2K's to ground are unnecessary. I've taken a E2S datapath card and oscilloscope to the RGB lines, they are not oversaturated when I took a look at them, infact pure whites were 252/252/252 (255+ would be over driven). You can skip them entirely.

You want RGB channels inline with 0.1uF caps on the inputs, put a 0.1uF bypass cap between 5V and GND on the amp and then 75 Ohm Resistors on the output inline of the RGB lines. If your RGB cable doesn't have 220uF capacitors you'll want to put one on each color channel inline on the outputs as well:

Thanks Pasky,
So basically I need to find 4 0.1uF caps for the project.

I always read the 1.2k resistors helped with the over brightness and checkerboard issues on the mini but I'm guessing the amp takes care of that with it's filtering.

Just curious what do the filter caps on the RGB inputs do, in case I can't add those right away until I buy some more.

 

[Pasky]

Thanks Pasky,
So basically I need to find 4 0.1uF caps for the project.

I always read the 1.2k resistors helped with the over brightness and checkerboard issues on the mini but I'm guessing the amp takes care of that with it's filtering.

Just curious what do the filter caps on the RGB inputs do, in case I can't add those right away until I buy some more.

"Checkerboarding" comes from noise in the sync signal, if you use CSYNC you won't get any. I think the misconception with the 1.2K resistors is people having different displays, I've measured with a scope and a frame grabber card and 6dB amplification on the RGB inputs doesn't overdrive any of them.

The 3 capacitors inline on the RGB inputs AC couples the signal. You'll want them there.

 

[ballzdeepx]

Right on Pasky thanks man.
This should be easy enough and I have a csync scart cable (looks like it just has pins for 1,2,3,4 and 11,12)
I'll grab some caps and get it done over the holiday.

Appreciate the details.

 

[ballzdeepx]

Well,
The mod went well except for whatever reason using a csync cable causes the picture to roll like mad on my pvm.
I used the same cable on a stock NA SNES and it works fine there so I don't know. Even adding a resistor to the sync wire in the scart hood didn't help.

Pin 18 on the RGB chip was wired to Pin 3 of the AV out for the csync mod.

I'm going SNES Mini>Sync Strike>PVM

I guess I'll just have to use compvideo sync on this one.

 

[segasonicfan]

read the THS7314 datasheet id regards to DC biasing - there are pull-up resistors needed as well. your issue is definitely sync related or system related though. Id recommend a JROK sync cleaner board if youre desperate. but a faint white line at the very bottom of the screen? after the signal is both upscaled and running on an lcd? I hope this modder didnt catch any trouble cause they did a quality job. I would be very pleased with those results on an upscaled setup.
note, my snes mini is rgb modded with the same chip and looks great on my crt. i suspect the setup being picky about sync.

 

[Xian Xi]

IMO, the 1.2K's to ground are unnecessary. I've taken a E2S datapath card and oscilloscope to the RGB lines, they are not oversaturated when I took a look at them, infact pure whites were 252/252/252 (255+ would be over driven). You can skip them entirely.

You want RGB channels inline with 0.1uF caps on the inputs, put a 0.1uF bypass cap between 5V and GND on the amp and then 75 Ohm Resistors on the output inline of the RGB lines. If your RGB cable doesn't have 220uF capacitors you'll want to put one on each color channel inline on the outputs as well:

Just to double check, have you checked on more than 1 unit? I've had to do the 1.2k ohm pull down on roughly 4 units while 10 others, no. I'm guessing it's a certain board revision that needs the pull down. All were modded the same way prior to the pulldown and those that needed them were WAY too bright.

 

[Voultar]

The 1CHIP ASIC has quite a wide swing on the RGB output levels. Some are pretty close to .7vPP. The grand majority that I've probed aren't anywhere near .7vPP.

Attenuation can be pretty important.

Here's a typical mini for you under peak luma load:



If you run that through a driver like THS7314 (that has a gain of 2/V) you're going to have ghosting, shimmering and a variety of reflection problems with the video output that will result in nasty shit on the screen.

1.2K is wrong, anyways. It's fine for the S-RGB encoder. But the S-RGB encoder doesn't have a fixed gain of 2. It's more in the 6.5dB range.

Let's look at something interesting.



That's a pretty decent manual measurement of the amplitude right off of the 1CHIP. What happens when it passes through the onboard encoder?



What the fuck, bitches? 1.74vPP? That figure should be around 1.616vPP if the encoder were a true 2/gain driver.

Well, it isn't. The on-board encoders gain output is 2.10V.


Here are a few measurements for different resistor pull-down values directly off the 1CHIP RGB outputs:

1.52K


1.62K


That's getting pretty close to .7vPP.

Like I said earlier, there can be a wide swing on the RGB outputs of the 1CHIP. I recommend a good optimal middle ground 1.8K pulldown to cover all of the bases, if you're using a Ti driver, that is.

Here's one that swings way out. YMMV!

 

[Pasky]

Just to double check, have you checked on more than 1 unit? I've had to do the 1.2k ohm pull down on roughly 4 units while 10 others, no. I'm guessing it's a certain board revision that needs the pull down. All were modded the same way prior to the pulldown and those that needed them were WAY too bright.

3 separate minis, one of them was a SNES jr I modded for a friend. It's possible it was a board revision, but all 3 I examined were the same revision, unsure if there are any revisions for the mini.