TI-99/4A websites that don't suck?

[missyrelm]

The more I think about this, the more I've been wondering what's the way to get the absolutely best possible picture from a TI-99/4A.

 

Here are my thoughts:

 

Getting the very best TI-99/4A picture:

 

With all this talk about swapping the 9918 chip with the 9928 to get component instead of composite, I feel like its time to step back and ask: “What will give the absolutely best picture out of a TI-99/4A?

 

So from reading different forums, mailing lists and groups, here’s the breakdown.

 

There are two links to fixes that have been posted on the TI-99/4a Google groups to get a clearer display before any type of chip swapping:

 

Clearer Display (Capacitor Fix)

http://www.mainbyte.com/ti99/display/display2.html

 

Clearer Display (Resisitor Fix)

http://www.mainbyte.com/ti99/display/display.html

 

I wonder whether these would actually still be needed after the chip swap?

If so, it seems a little silly to take the time to swap the chips and not do the above to “sweeten the deal” so to speak…

 

So everyone seems to agree that the way to go is to swap the 9928 from 9918 to get component instead of composite, and that this will output R-Y, B-Y, and Y.

 

So the real question is where to go from there:

Obviously you are limited to the inputs on your monitor or TV, but what if you had your choice?

 

I’m a good guinea pig for this, as my HDTV takes a bunch of different types of inputs:

(I bought it with the express intention of being able to attach as many vintage consoles to it as possible, so I purposely got one with many different types of inputs)

 

It has “modern” inputs too, but the ones of interest are:

 

2 Component video inputs

2 S-video inputs

2 A/V inputs

PC input

RF antenna inputs

 

The question is what type of input will give the very best picture once the 9928 is put in:

 

As far as I can tell, the options are:

 

1) Stick to component

 

At first I was certain that S-video would give the best picture, now I’m not so sure.

The question is will all that converting degrade the signal to the point that it’s actually not giving the best picture. I’m beginning to wonder if all I need to do to get the best picture is to get the chips swapped, and maybe get the capacitor and resistor fixes done as linked to above, and leave it at that….

 

I tried calling Samsung to ask if the component inputs would take R-Y, B-Y, and Y,

And it was obvious that they had no idea what I was talking about, but

I’m guessing that if I used this and it worked, I’d want to set the resolution on the TV down to 480p, and set the picture to 4:3.

 

2) Component -> RGB

Is there any reason why this would be more clear than the component? I’m starting to wonder, though the nice thing about this is many more monitors would support this.

 

Major props go to Djpuppa for working on this! You're the man!

 

We'll have to see how this goes....

 

3) Component -> RGB -> S-Video

 

At first I thought this is what I wanted to get the clearest picture, just because that’s what everyone seems to want to convert old consoles to. Now I’m not so sure. It seems like there’s a lot of converting here, and I wonder if the signal will degrade to much during all of that…

 

If there was a way to go straight from Component to S-Video maybe that would be different, but I haven’t heard of anyone doing that.

 

Any thoughts on what would give the absolutely best picture possible?

[Tursi]

The cap and resistor changes date back to when the TI was still actively sold. They make some improvement in most cases, but it depends on what you're using for a monitor. The resistor change is actually based on the 9918 datasheet, and should give faster rise and fall times. The cap change may have no effect depending on the monitor it's used with (some have a cap inline already).

 

The component output of the 9928 is not what we call 'component' today (at least as far as I understand - I haven't confirmed by experimentation!) So it needs to be converted into a usable form anyway. If you can find out from someone else that there are devices that take that signal, that would be great to know!

 

To that end, my *opinion* is that converting to RGB or S-Video, either should produce comparable results. My opinion is that the 9928 signal is closer to S-Video anyway, and you can't (really) get a better signal than your input, so I would expect that with a decent converters the S-Video and RGB video would be very, very close.

 

You should be able to convert to S-Video without the intervening RGB state, I think...? I thought that was what the ColecoVision circuit did on its way to composite? (The luminence information is already there on the Y line, you just need to generate the chroma information).

 

I wonder whether these would actually still be needed after the chip swap?

If so, it seems a little silly to take the time to swap the chips and not do the above to “sweeten the deal” so to speak…

 

Just wanted to add this - if you swap out for the 9928, you can't really use the video amp on the TI mainboard, so the cap and resistor changes would no longer be relevant.

Edited October 8, 2007 by Tursi

[djpubba]

Read this:

 

http://www.projectorcentral.com/component.htm

 

I think R-Y, B-Y, Y is component video. I think the signal coming from the 9928 would need to be amplified to be used though.

 

My interest in converting the signal to RGB is more for convenience than for the best possible picture. I've got a lot more RGB monitors than I have TVs with component video. The picture quality is going to be a lot better than composite either way. I doubt I'd be able to percieve a difference between RGB and component, so I'm going to be as happy as a clam with RGB.

Edited October 8, 2007 by djpubba

[djpubba]

For kicks, I tired connecting the output of the 9928 directly to the component inputs on my TV with no amps or anything. On boot, it looked pretty nice! (see pic 1). Can't really tell from the pic, but the colors look a little over-saturated. However, when I started Miner 2049er, the background was blue instead of black and the colors were way too saturated. (pic2)

 

So the signal definitely needs some additional circuitry to feed a component-input TV. It should be identical to a ColecoVision->component video mod. I've got an 8-bitdomain.com ColecoVision mod on the way from Bill Brasky, so when that arrives, I'll give it a try just for fun.

Edited October 9, 2007 by djpubba

[Tursi]

Aw, beautiful! Thanks for trying that and thanks for the link to the component description. I now know a lot more about the 9928 than I did at the start and it's all good stuff.

 

Time to get my hands on one.

[missyrelm]

Djpubba, you're the MAN!!! I second Tursi, thanks for trying that... It's great to learn so much about the component output of the 9928...

 

 

For kicks, I tired connecting the output of the 9928 directly to the component inputs on my TV with no amps or anything. On boot, it looked pretty nice! (see pic 1). Can't really tell from the pic, but the colors look a little over-saturated. However, when I started Miner 2049er, the background was blue instead of black and the colors were way too saturated. (pic2)

 

So the signal definitely needs some additional circuitry to feed a component-input TV. It should be identical to a ColecoVision->component video mod. I've got an 8-bitdomain.com ColecoVision mod on the way from Bill Brasky, so when that arrives, I'll give it a try just for fun.

[ti99_forever]

For kicks, I tired connecting the output of the 9928 directly to the component inputs on my TV with no amps or anything. On boot, it looked pretty nice! (see pic 1). Can't really tell from the pic, but the colors look a little over-saturated. However, when I started Miner 2049er, the background was blue instead of black and the colors were way too saturated. (pic2)

 

So the signal definitely needs some additional circuitry to feed a component-input TV. It should be identical to a ColecoVision->component video mod. I've got an 8-bitdomain.com ColecoVision mod on the way from Bill Brasky, so when that arrives, I'll give it a try just for fun.

 

Have you tried some color tests from TI Basic?

 

I remember my 9938 giving some slightly different colors than the 9918A (but not blue instead of black).

 

Sure you didn't have a lose connection? B/c now I remember getting weird color changes like that due to my poor soldering skills on my monitor cable I made for my 9938...

[Tursi]

I ordered a few 9928s for my own experimentation. I don't need another project, but this is too cool.

[djpubba]

I got ahold of the ColecoVision video mod from 8bitdomain.com and gave it a try on the TI. It didn't work very well. It gave similar results to just feeding the signal straight into the TV, except with more interference. Anyone know the pinouts of this thing or some real schematics for the ColecoVision? I figured out most of them from tracing things and looking at Dan Boris's ColecoVision schematics:

 

P1 (Audio Out)

1 - Audio

2 - GND

3 - Audio

4 - GND

 

P2 (Video out)

1 - GND

2 - Luma?

3 - Composite?

4 - Chroma

 

P3 (Component Out)

1 - B-Y

2 - Y

3 - R-Y

4 - GND

 

P4 (Power & Audio In)

1 - +12vdc

2 - ??? not sure what this is

3 - Audio In

4 - GND

 

P5 (Video In)

1 - B-Y

2 - R-Y

3 - Y

4 - GND

 

P6 (Power LED)

1 - GND

2 - Vcc

 

Sure you didn't have a lose connection?

 

Yes, I'm sure. I'd consider that something might be wrong with my connections or the 9928 except that it looks nearly perfect using Gorf's RGB interface board on a multisync monitor with sync-on-green. So I don't think that's it.

 

If I connect just Y, I get a beautiful, crisp greyscale image. Connecting either of the colors produces an image with way too much saturation. I suspect that the p2p voltage on the color lines is out of range. Probably with the 9928 installed on the ColecoVision there is some additional circuitry there that adjusts the p2p voltage levels to the correct range before it gets to the 8bitdomain board. In fact, I see that there is but I'd have to trace things out a bit more to be sure that's what's wrong.

Edited October 16, 2007 by djpubba

[djpubba]

For more kicks, I hooked up a couple of 100k pots between the 9928's B-Y and R-Y outputs and the TV's component inputs. By adjusting the pots, I was able to get really nice colors. The picture looked great. Looking at the data sheet for the 9928, I think it just needs some pull-down resistors on each line.

Edited October 14, 2007 by djpubba

[ti99_forever]

You're killing me! Where are the pics!

[djpubba]

You're killing me! Where are the pics!

 

I'm sure it's not the right way to do it, but I just added 470 ohm pull-down resistors to each line and then a pot on R-Y and B-Y which I adjusted until the colors looked right.

 

Seaching for info on modding the ColecoVision, I found folks talking about the need for a buffer to protect against shorts.

 

http://nfggames.com/forum/index.php?showto...ost&p=19897

 

I doubt I'll bother building a proper circuit for this since I'm going to go with RGB as soon as my Vidiot arrives (why must everything I buy for this project take weeks to arrive?)

 

Picture attached.

[djpubba]

My Vidiot arrived today. Oh. Oh. Oh. So nice.

 

It took quite a bit of adjusting to get a beautiful picture, but I got one. The voltage filter on the Vidiot was shot (probably why it was sold for parts). Once I fixed that, I still had a problem with the +12vdc getting converted to +7.6vdc instead of +8.2vdc which the schematics called for. The colors we bleeding badly and the sync was touchy. I replaced R106 (a big resistor) with a pot and adjusted it with a volt meter until it was getting +8.2vdc exactly. That fixed the bleeding issues. Then it was just a matter of adjusting the color pots on the Vidiot to get nice colors. It's beautiful. See pics attached. The second picture is a little blurry because of the camera's focus, not the LCD. It looks very nice. Lovely RGB from my TI!

 

I need to try this on a ColecoVision now to see if it has those vertical lines like you get with all the other video mods for Coleco.

Edited October 16, 2007 by djpubba

[Longhorn Engineer]

My Vidiot arrived today. Oh. Oh. Oh. So nice.

 

It took quite a bit of adjusting to get a beautiful picture, but I got one. The voltage filter on the Vidiot was shot (probably why it was sold for parts). Once I fixed that, I still had a problem with the +12vdc getting converted to +7.6vdc instead of +8.2vdc which the schematics called for. The colors we bleeding badly and the sync was touchy. I replaced VR4 (a big resistor) with a pot and adjusted it with a volt meter until it was getting +8.2vdc exactly. That fixed the bleeding issues. Then it was just a matter of adjusting the color pots on the Vidiot to get nice colors. It's beautiful. See pics attached. The second picture is a little blurry because of the camera's focus, not the LCD. It looks very nice. Lovely RGB from my TI!

 

I need to try this on a ColecoVision now to see if it has those vertical lines like you get with all the other video mods for Coleco.

 

got a link to the schematic to the Vidiot board? I can't seem to find it via google.

 

After reading all this from what I understand is that

 

1. Replace the 9918 with a 9928

2. Placed 470 ohm pull downs on the 3 outputs (Y, B-Y, R-Y)

3. Coupled with a Vidiot

4. Tweak pots on Vidiot

5. Awesomeness ensues

 

Looks like it would be pretty easy to get S-Video from there if you wanted it.

Edited October 16, 2007 by Longhorn Engineer

[Jess Ragan]

Is vertical striping common on old game systems connected to LCD monitors? I'm noticing this on both my 2600 Jr. mod and 8-Bit Domain's 5200 mod, and it's extremely irritating!

[djpubba]

No vertical striping on the TI mod. I'll try it with a Colecovision shortly.

 

The Vidiot has its own pull-downs so skip step 2.

 

The Vidiot is HUGE so it's not going to fit inside the TI's case. The good news is that the circuit we need is isolated and can be cut out of the board. It's still going to be tough to squeeze it inside the TI's case. Probably better to replicate the circuit with smaller, more modern components. There's also the matter of killing fairly rare Vidiots for this mod, which isn't a good idea to do en-mass.

 

Vidiot schematics here (pages 47-48):

 

http://arcadecollecting.xmission.com/rgvac/babypac.pdf

Edited October 16, 2007 by djpubba

[djpubba]

I took s'more of pictures of the TI connected to a nearly brand-new RGB arcade monitor (Happ Vision Pro. Got 'em on sale from happcontrols.com for $130/ea). The quality is stunning.

 

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0464.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0466.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0478.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0480.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0483.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0487.JPG

 

I also tried it with the ColecoVision. The vertical striping is still there but not nearly as bad as it was using s-video with the 8-bitdomain mod. I also tried pulling the pins up on the 9928 so the signal goes straight into the vidiot and it improved the picture even more. Doing it that way, the striping is just barely detectible in the blues (see the skill select and Time Pilot pictures — you can just barely see it. That's what it's like, but ignore the horizontal lines. Those are from the camera.)

 

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0494.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0499.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0505.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0509.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0511.JPG

http://arcadecollecting.xmission.com/Arcad...ot/IMG_0513.JPG

Edited October 16, 2007 by djpubba

[Tursi]

Awesome!! Thanks for posting the pictures!

 

I can't wait to play with this myself.

[mos6507]

Is vertical striping common on old game systems connected to LCD monitors? I'm noticing this on both my 2600 Jr. mod and 8-Bit Domain's 5200 mod, and it's extremely irritating!

 

It happens on the 2600 and 8-bit machines. It just has to do with how the chips work.

 

If you don't like it use composite instead of S-video and it will smooth it out.

[Longhorn Engineer]

adding a 100pf cap in line with chroma line should soften the lines without effecting the sharpness

[djpubba]

Just a quick note that I was able to cut the RGB circuit out of the Vidiot board and it fits nicely inside the TI's case.

[ScottHuggins]

Wow, AWESOME work. Really interesting project. I have a massive I collection (the whole PEB, modem, etc). Still love to play with it from time to time.

 

Just a quick note that I was able to cut the RGB circuit out of the Vidiot board and it fits nicely inside the TI's case.

[missyrelm]

This is sooo cool! Thanks for posting about your experiments.

 

I have tried to make other forums with people who might find this process very interesting aware of your success...

 

There is especially a lot of interest on the ti99-4a Yahoo Group about this, and at least one person there has ordered parts to try it. From the tone of other people there, other people will be trying it too at some point.

You have to be approved to get in, and the messages that are specifically about this can be a bit hard to find, but there are people there delving further into this mod ATM and while it all started here, it's probably another good place to check for people further interested in this mod.

 

I suspect that the "9928 upgrade" will become semi-common for hard-core TI-99/4a'ers but even if it doesn't, it's really cool what you've done!

 

Just a quick note that I was able to cut the RGB circuit out of the Vidiot board and it fits nicely inside the TI's case.

Edited October 19, 2007 by missyrelm

[Longhorn Engineer]

I looked into building the Vidiot. Problem is that it uses an obsolete part. Trying to find an equivalent.

[djpubba]

The LM359? Go Jameco.

 

http://www.jameco.com/webapp/wcs/stores/se...roductId=839391

 

I've been experimenting with various RGB monitors. The non-arcade monitors like the Commodore 1084 and the Sony CPD-1302 need some resistors on the RGB output lines from the Vidiot to look good. The 1084 looked best with 75 ohm resistors. The CPD-1302 looked best with 110 ohm resistors.

 

This mod on a 1084 is jaw-dropping. Amazing quality.

 

The next thing I need to try is running it through an XRGB-2 (scanline converter) to see how it looks on a VGA CRT monitor, and then a VGA LCD monitor.

 

I found another Vidiot to use on a ColecoVision. Same seller as the last one. Turns out he had two!

Edited October 19, 2007 by djpubba