ColecoVision Component Video Mod

[Ikrananka]

Over the past few years I have aspired to obtain a ColecoVision component video mod that works well on modern HD LCD TVs. Firstly I had hoped to buy one from Viking Video Games (doubledown) but unfortunately he has stopped supplying standard video modded CV's to order years ago. I then thought I'd try the 8bitdomain mod which, along with composite and s-video mods, includes a component video mod. I installed this mod around a year ago but unfortunately it didn't work well with my LCD TVs - posted my experience with it here. Discussed this with 8bitdomain who said that, in the near future, he would be releasing a new mod specifically designed for HD TVs - a year later and this has not materialised. So, I decided that the only way this is going to happen for me is to try and do it myself - problem is I have very little knowledge of electronic circuits - but I am handy with a soldering iron and a multimeter and reckon this should be a fun challenge

 

So over the past few months I have been doing as much research on the internet as I can and have found some very useful information. There are lot's of details describing how to do mods for composite and s-video but little tangible information about a component video mod. There are a few threads that discuss, or touch on, this subject but none of the ones I have found run to completion with any component video mod schematics and/or screen shots, e.g.:

 

http://nfggames.com/forum2/index.php?topic=2925

 

http://www.atariage.com/forums/index.php?s...05191&st=50

 

From what I have read there does appear to be a need to amplify the Y, R-Y and B-Y signals from the TMS9928 VDP and there are typically two ways of doing this, one using transistors and the other with op-amps. Now the op-amp circults are much more complex than the transistor based ones and so I reckon I'll start with the transistors and move to op-amps later if necessary. The other thing I have concluded is that I really need to be able to adjust the strength of each signal (Y, R-Y & B-Y) to get the picture right and so I need to include pots on each line.

 

Based on the above I have knocked up a simple schematic (attached). Probably going to head out and buy the components next weekend and knock up a proto board. In the meantime any constructive comments woud be most welcome. Things I am questioning are:

 

1. Do I need 75 ohm resistors on all three output lines or just on Y?
   
2. Do I need capacitors on the B-Y and R-Y lines to remove the DC component of the signal?
   
3. Are the pots in the right place, i.e. adjusting the voltage to the transistors, or should they be on the signal lines?
   

 

Many thanks for ANY help.

Transistor_Schematicv0.1.pdf

[+5-11under]

Hi Ikrananka,

 

I've done some work on this a while back, and am just getting started back onto the project as of yesterday. The problem I've had is variability between TV sets/monitors. On my TV, I get some corners of pixels flickering on/off on the top half of the screen, as well as vertical banding. However, I tried it out on a smaller TV yesterday at a video game show, and it looked great. Someone complained that you could see the pixels (ie. no smearing), but that's another story. I also get a lot of colour variability between TVs. I'm not sure if that's my fault or just the way it is. I'm still happy with the picture I get on my TV, but I'm hoping to get it better, and be able to have higher consistency for all/most TVs.

 

Sorry, I'm not great at understanding transistor circuits, but I'd keep the same 75 ohm circuit on each path. Remember, too, that just having the "Y" connected should get you a monochrome picture. The Pb and Pr output levels from the VDP vary somewhat from the Y level, if I recall correctly, so the amplification pot position will be different. Also, I think the output of the VDP actually needs to be attenuated, but I'm guessing most transistor amplifiers would be able to do that. Just do your best to start the circuit at the "zero" level before cranking it up to 11.

 

Thanks,

5-11under

[Ikrananka]

Hi Ikrananka,

 

I've done some work on this a while back, and am just getting started back onto the project as of yesterday. The problem I've had is variability between TV sets/monitors. On my TV, I get some corners of pixels flickering on/off on the top half of the screen, as well as vertical banding. However, I tried it out on a smaller TV yesterday at a video game show, and it looked great. Someone complained that you could see the pixels (ie. no smearing), but that's another story. I also get a lot of colour variability between TVs. I'm not sure if that's my fault or just the way it is. I'm still happy with the picture I get on my TV, but I'm hoping to get it better, and be able to have higher consistency for all/most TVs.

 

Sorry, I'm not great at understanding transistor circuits, but I'd keep the same 75 ohm circuit on each path. Remember, too, that just having the "Y" connected should get you a monochrome picture. The Pb and Pr output levels from the VDP vary somewhat from the Y level, if I recall correctly, so the amplification pot position will be different. Also, I think the output of the VDP actually needs to be attenuated, but I'm guessing most transistor amplifiers would be able to do that. Just do your best to start the circuit at the "zero" level before cranking it up to 11.

 

Thanks,

5-11under

Hi 5-11under,

 

Thanks for the reply. Sounds like you're far more progressed on this than I am. Nevertheless, I'm going to have a play and build up some circuits to see what I can get. One of the problems I have seen with the three composite modded CVs I have is that on certain games and on different TVs I'll get the top 25% of the screen suddenly tearing and jerking left and right - mainly happens on games with lots of the same bright colour or white background (Turbo in the snow scenes and any Magical Tree scene). I wonder if this is similar to what you've experienced with your component mod.

 

I have managed to get the clear monochrome picture - looks great but goes completely wrong when also directly connecting the R-Y and B-Y line (way too much blue and streaky).

 

I suspect that most of the problems could be solved if I can get the correct voltage on the amplified output, i.e. 2Vp-p (assuming that this is then followed by a 75ohm resistor).

 

I'm not sure what you mean by attenuating the VDP output - doesn't this mean the opposite of amplification - so why reduce signal strength to then only increase it again?

 

Don't suppose you'd be willing to share your circuit diagram?

 

Thanks for any help you can give and I'll let you know how I get on.

[GonzoCV-1]

Hi,

 

Remember that the TMS9928 puts out a color difference signal, not true R.G.B.

 

Here's s circuit I have from a TMS9928 book that is supposed to be a multi-video connection option. Its modular, so obviously you would omit PAL stuff. But it will output true RGB.

 

I know its more complicated than you're interested in seeing, but alas, it is what it is. If need be, I can find the whole publication and try to upload it as a pdf.

 

[Ikrananka]

Hi,

 

Remember that the TMS9928 puts out a color difference signal, not true R.G.B.

 

Here's s circuit I have from a TMS9928 book that is supposed to be a multi-video connection option. Its modular, so obviously you would omit PAL stuff. But it will output true RGB.

 

I know its more complicated than you're interested in seeing, but alas, it is what it is. If need be, I can find the whole publication and try to upload it as a pdf.

 

I am after component video and not RGB - at the moment anyway

 

The schematic is most interesting - would be wonderful if you could scan and upload the entire document - may well provide some valuable pointers.

 

I'm working up a component video schematic but I've been swamped at work and it's on hold for the next two weeks. Will progress and build a prototype in June.

[Murph74]

Hi,

 

Remember that the TMS9928 puts out a color difference signal, not true R.G.B.

 

Here's s circuit I have from a TMS9928 book that is supposed to be a multi-video connection option. Its modular, so obviously you would omit PAL stuff. But it will output true RGB.

 

I know its more complicated than you're interested in seeing, but alas, it is what it is. If need be, I can find the whole publication and try to upload it as a pdf.

 

I am after component video and not RGB - at the moment anyway

 

The schematic is most interesting - would be wonderful if you could scan and upload the entire document - may well provide some valuable pointers.

 

I'm working up a component video schematic but I've been swamped at work and it's on hold for the next two weeks. Will progress and build a prototype in June.

 

I am definitely interested in this, too, still. I've yet to even composite mod one of my CV's, but use a composite modded Atari thru a DVD recorder on to my component-based projection system with no problems. It's a long way around to get component video, but functional. And no noticeable lag.

 

Murph

[Ikrananka]

After a few months of research and planning I finally landed on a schematic design that I felt comfortable with (attached). This schematic is based heavily on the schematic from the TMS9928 "Interface to Color Monitors" application report that GonzoCV-1 kindly posted in this thread (I found the full report elsewhere - also attached). Reading the text of this report it seemed to make a lot of sense to use the Sync Separation and DC Restoration parts while simply running each restored signal line (Y, R-Y and B-Y) to a dedicated op-amp should provide well conditioned and amplified component video signals.

 

So I spent a lot of time identifying what I thought were suitable parts and ordered them. To simplify the circuit I replaced the TI schematic's sync separator circut with a single EL1881 sync separator chip. Following advice on another forum I used more modern op-amps (LM6172) compared to the older ones (LM318) in the TI report. I also noticed what I believe are some typos in the TI report's schematic around the CD4066B chip's pin numbering and adjusted as follows:

 

Before => After

2 => 3

3 => 2

5 => 13

13 => 5

 

I also noticed that the TI schematic didn't show any power supply to the CD4066B chip. For my first pass I decided to include power and so added +5V to pin 14 and routed pin 7 to ground.

 

I also included trimmer pots on the gain feedback lines to each op-amp to enable me to tweak each signal.

 

So I built the circuit and hooked it up to a 26" LCD TV. Much to my disappointment the picture was jerking badly from left to right with the jerking being much worse at the top of the screen and getting better towards the bottom. In addition, the colours were wrong with black being a very strong blue colour and the other colours just generally being wrong (except white and blue seem okay). See attached pictures. Adjusting the trimmer pots brings about little discernable difference. I wondered if my adding power to CD4066B was contributing to the problem, however disconnecting the power and ground from pins 14 and 7 made little difference to the image.

 

Have I overcomplicated this? Is the TI schematic overkill? Have I interpreted it incorrectly? Should I just be looking at running each raw TMS9928 output straignt through an op-amp without additional conditioning? Unfortunately I am not an EE and do not have an oscilloscope to analyse the signals - not that I know how to use an oscilloscope or interpret its signals anyway!!!

 

I'm willing to try anything but really need some expert/experienced advice. 5-11under - perhaps we could collaborate. Doubledown - I know you've successfully created a component video mod - any pointers from you would be gratefully received.

 

Much appreciate any help anyone can give.

CV_Component_Video_Mod_v0.1.pdf

TMS9928_Video_to_Monitor_Application.pdf

Edited June 22, 2009 by Ikrananka

[ten-four]

Hi Ikrananka...

 

As you can see in this picture, so I actually got the same result as you.

 

 

The picture are from march 2008.

 

I could not make it work.

 

Maybe the solution is hidden in this chip: AD_725.pdf