Cause found & solution for Pink / Magenta / Purple tinted video on MiSTer I/O Board analog VGA output

[trackball]

There were some previous threads about this topic and the symptoms described below on the older Atari forums, but they had been locked, so I am posting this solution here in a new thread.

I had purchased a MiSTer I/O board (v5.2) from a fellow forum member many months ago. The person selling it had assembled it themselves, but the board was incomplete, and missing many of the surface mount resistors and capacitors, as well as the DE-15 ("VGA") connector for the analog video output. After using it for many months mainly for the cooling fan and convenient buttons on top, I decided to order the missing parts and solder them in place to finish the board myself, so I could use the analog video output.

After soldering everything in place, I connected the I/O board back on the MiSTer, and connected a VGA-compatible monitor to the analog video connector. The video signal appeared on the analog monitor! Unfortunately, while sharp and stable and otherwise correct, it had a pinkish or purplish tint to it. The video displayed correctly and with normal colours on the HDMI connector, so the issue seemed to be isolated to the video output on the I/O board.

This pink or purple color stayed no matter what I tried. It was the same on every monitor I tried, every video cable, and with every setting I tried in the MiSTer's .INI file. I also tried re-flowing solder on the VGA connector, and on many of the surface mount components on the I/O board, in case there was a bad connection.

I found multiple reports of people experiencing the exact same symptom with their MiSTer I/O boards when I searched online, but there never seemed to be a very clear resolution as to how they made the pink tint go away, or if they ever fixed the problem they had. Most people seemed to have just replaced their MiSTer I/O board with a new one in order to make the issue go away. I figured I had nothing to lose by trying additional things and seeing if it made it better or worse.

Since the image being outputted on the video connector was recognized correctly by the monitor, and other colours were present in the image, my guess was that the pinkish tint on everything on the display was being caused by either too much of something signal-wise being sent to the monitor, or else too little of something.

When searching online for articles about what would make a VGA video image appear pink or red, I found a mention somewhere saying that a LACK OF THE GREEN VIDEO SIGNAL would make a VGA image on a monitor appear very pink or purple.

I started looking at the schematic for the MiSTer I/O board, and saw that the green video signal goes through the resistor array, and then heads down to a slider switch, where the user can switch between standard video, or sync-on-green video. If the switch is not installed on the I/O board, no green signal is passed along to the video output. The switch handles passing the green video in each of those two video styles, but it must be present or else no green signal of any kind gets sent through.

Sure enough, I looked at my MiSTer I/O board, and the switch was never installed. I never thought to order one when it didn't come already present on the board - I just figured it was optional, since I wouldn't be using sync-on-green. IT IS NOT OPTIONAL - YOU NEED SOMETHING IN PLACE HERE to make an signal connection. I quickly soldered in a jumper made from a wire between the two holes on the board enabling the standard-style video's path for the green signal. On my VGA monitor, the pink or purple tint was gone, and the analog video output now looks perfect!

I will be ordering a proper switch soon so that I can finish the board, but for now, this has solved the problem on my I/O board.

If you are experiencing a pink or purple tint on your I/O board's analog ("VGA") video output, I would encourage you to look at the schematics for your I/O board, follow the green signal's path while looking at your actual I/O board, and confirm that the sync-on-green DPDT slider switch (listed as SW4 on MiSTer I/O board v5.2) is installed and is working properly.

Hopefully this helps someone else who runs into the pink or magenta tint on their analog video and can't figure out where to start!

[Nat]

Basically a good rule of thumb when building MiSTer boards is unless it is marked on the circuit diagram as DNI (Do Not Install) all components should be installed unless you are certain of the ramifications of leaving certain components uninstalled when building addon boards.

[Sigismond0]

Good stuff, though I'll throw a small wrench into this and say that my board came with a SOG switch installed (and it works correctly as I'm using RGsB to my PVM), but I still get pink VGA ouput no matter what I do. Not a big deal for me since I'm not using VGA natively, but others might have the same issue.

[trackball]

Good stuff, though I'll throw a small wrench into this and say that my board came with a SOG switch installed (and it works correctly as I'm using RGsB to my PVM), but I still get pink VGA ouput no matter what I do. Not a big deal for me since I'm not using VGA natively, but others might have the same issue.

Think back about what you're describing here -- we know you have a green signal at the switch, because when the switch is in SOG mode, it passes green along fine to your PVM (and adds sync to it). However, when the switch is in "VGA" mode, you get the pink tint on the VGA image. It sounds like the green signal isn't being passed through the switch when it is positioned in VGA mode (eg. the VGA side of the DPDT switch isn't working properly). I would replace the switch! You could remove the switch and put a jumper in the appropriate holes for the switch for VGA mode on the board like I did and prove it that way before ordering anything. Even if I wasn't using it, I'd rather not have half working stuff if I didn't have to.

[trackball]

Basically a good rule of thumb when building MiSTer boards is unless it is marked on the circuit diagram as DNI (Do Not Install) all components should be installed unless you are certain of the ramifications of leaving certain components uninstalled when building addon boards.

I hear you - I wish I wasn't working backwards from a half-finished board to begin with.

[pokevania]

I ran into this issue after a clean format. To fix the pink/ purple hue, the ypbpR option must be enabled in /media/fat/MiSTer.ini. It's off by default.

[Psykoth]

I had this same issue with a pink hue over component to a Sony Trinitron TV that was picky about the signal. (Component worked on other TVs.) What finally fixed it was changing I/O boards to the Mister Addons Analog I/O Pro.

I am using a Retro Gaming Cables component (10-pin) cable, which has the benefit of wanting a RGB signal (set that in the Mister.ini, instead of ypbpr) which allows me to have component video and direct video both at the same time.

[cybort]

So it seems I managed to overlook this thread (and obviously I used the wrong search terms) when I posted my thread about the same issue (@mods feel free to merge my thread with this one).

I'm using a pre-build A/V Pro 9.2 (bought from UltimateMister) and I'm having the pink tint issue on the VGA output. I already tried several MiSTer.ini config variations (also the ones mentioned here in this thread) without success. There isn't a SOG switch on my board (as suggested in the first post) and looking at the schematics (assuming these and these are the correct ones) I checked the traces for the green signal from the A/V boards U1 IC to the VGA connector and everything seems to be fine.

Any ideas/guesses what may be wrong with my config or board and how to fix it?

[KennyL]

Looking at your ini, maybe set vga_sog=1?

[cybort]

Already tried that - doesn't help unfortunately.

[rickdangerous]

Already tried that - doesn't help unfortunately.

Hello send me email from the site and I check what is including I send you a MiSTer INI to you test. Have you reseat the AV module?

[cybort]

Already tried that - doesn't help unfortunately.

Hello send me email from the site and I check what is including I send you a MiSTer INI to you test. Have you reseat the AV module?

Thanks, I've just sent you an email.

I've reseated the AV module several times - no change in the pink tint unfortunately.

[cybort]

Ok, in my case, it turns out I was just being stupid.

I downloaded the 240p Test Suite with the intention of perfecting the geometry settings of my CRT. I noticed there was a White Screen test included and when I started it, my CRT displayed a perfectly white screen.

It turns out the menu has a slight pink tint (at least on VGA - it's almost not noticeable on my HDMI screen) - and that confused me into thinking that the pink tint was on the VGA output.

So in my case it came down to me being a noob in all things MiSTer. Sorry for wasting everyone's time! And special thanks to rickdangerous for providing e-mail support!

I'm attaching a photo of my CRT with the White Screen test and the menu open. Maybe my experience will help other noobs in the future.

IMG_0589.jpeg (587.43 KiB) Viewed 1719 times