Let's design a new video mod

[Rygorn]

Came across this thread while searching out a more available replacement for the FMS6400/6410. Has anyone had any luck in finding one? Or am I going to be stuck designing something new from the ground up that uses something different?

[+-^CrossBow^-]

I haven't personally tested this board as I haven't gotten any requests to mod any 2600s and usually have left those for Osgeld to do. But maybe give this one a shot and see how results you get?

 

https://www.ebay.com/itm/ATARI-2600-MOD-PCB-KIT-BEN-HECK-SVIDEO-COMPOSITE-STEREO/332747559437?hash=item4d794cd20d:g:pgMAAOSwqQBbZgP5:rk:38:pf:0

[Osgeld]

mouser has the 6410's still in stock but it is an obsolete part

 

 

https://www.findchips.com/search/fms6410

[Rygorn]

mouser has the 6410's still in stock but it is an obsolete part

 

 

https://www.findchips.com/search/fms6410

Yeah.... I can still find them in a few places, but I was hoping to design a mod around something newer to keep it a little more sustainable. Designing around an obsolete part is never a good practice. Sure if I just want one or two for myself I could build based on that, but I'd rather add to the community with something new focused around parts that wont run out anytime soon.

[Rygorn]

I haven't personally tested this board as I haven't gotten any requests to mod any 2600s and usually have left those for Osgeld to do. But maybe give this one a shot and see how results you get?

 

https://www.ebay.com/itm/ATARI-2600-MOD-PCB-KIT-BEN-HECK-SVIDEO-COMPOSITE-STEREO/332747559437?hash=item4d794cd20d:g:pgMAAOSwqQBbZgP5:rk:38:pf:0

I saw those..... Looks like a surface mount version of the LHE mod. Kinda similar to what I'm trying to design, but would like to see if I can squeeze a little better performance out of my design. If I get something working I'll sell the PCB's if people want them, but I'll also open source the design files if anybody wants to order their own from somewhere. I don't see the 2600 selling enough mods for me to want to keep my design to myself. Not to mention just about anyone here could probably reverse engineer it anyway lol.

[+batari]

On 2/3/2013 at 1:16 AM, batari said:

The mod started as a combination of the CD4050 mod from the AA FAQ, along with a copy of some of the 2600's own video circuitry, then run into a video filter/amplifier chip. I took another look at it all, removed/added parts by experimentation, and came up with my own mod. It looks pretty good in general, but I agree, the composite could be better. What seems to help is an additional 75 ohm load to ground on the composite line, but this "shouldn't" help in theory.

 

So I decided to redesign everything, literally everything, from scratch. I will take ALL TIA pins and lift them (no longer are we relying on ANYTHING on the 2600's board) and put them together to try and recreate a proper NTSC signal.

 

This is what I learned:

BLANK level is 0v

BLACK level is about 0.1v

WHITE level is 1.0v

SYNC pulse is -0.4v

COLORBURST is +/- 0.2v

AUDIO is about 1.4v RMS (??)

 

The negative voltages are a pain to produce and I don't think they are strictly necessary, so I shifted everything up by 0.4v. The circuit can be AC coupled to remove the DC offset if needed.

 

I have carefully chosen parts so I can get somewhat close to these values. I plan to simulate this circuit in PSPICE as well. I've also axed the CD4050... I really don't think it's necessary if this mod is done right and it actually makes some things worse. I used a pair of MOSFETs in a common-drain configuration to provide unity voltage gain but current amplification on both the Y and C subcircuits, then tied each to a load resistor. I expect that the output of the FETs should be "good enough" to produce a nice video signal on their own but I'll go ahead and run it through the filter anyway.

 

I'll post the new schematic after I have a chance to actually simulate in PSPICE, then build it and see how good it is, then tweak to try and match the actual NTSC spec as close as I can, and THEN connect to the TV and see how it looks. I don't have a solid timeline for this but if I do get somewhere, I'll post what worked.

I never did finish this, at least not that I can remember. I don't think I ever ran it through PSPICE either.

 

The original intent of this post in 2013 was to reduce complexity but retain functionality. To me, an ideal video mod is one that functions very well (but not necessarily perfect) while being relatively simple and cheap to produce, use as few parts as needed and employ through-hole parts wherever possible, and to not rely on any ICs, especially not SMT ICs that are no longer made.

 

This is what I came up with back in 2013:

 

 

I don't know if this is complete or not or even that this circuit will work at all. Plus, I did a quick search for BSS110 (it's a P-channel, enhancement mode Mosfet) and it's not an active product anymore, but I am sure there is a suitable cross-reference for it. ZVP4424A seems closest, but the cheaper ZVP3310A might work too?

 

In order to most closely hit the voltages above, I thought I would put pots in for everything, plus this allows for maximum flexibility for various TVs, so you can find the display that works best for you.

 

The circuit was intended to support S-video or Composite, but not both at the same time. S-video does not need the inductor. If you want composite, add in the inductor L1 to combine the two signals, and the inductor also helps with filtering. I am not sure that the 15 mH value is ideal, so anyone who wants to experiment with this should have various inductors on hand.

 

R9, R10 and the volume control pot are optional. Plus, looking at it now am not sure how well the volume control would work anyway.

 

If anyone builds this, post up results here! Note this was never tested, and it has been so long I don't even remember how or why I came up with this: I am merely posting the file with the latest date on it!

 

 

vidmod_basic.zip