TMS9929 (Sega etc.) display direct to modern TV!

[honestbob]

Good idea contacting him. You could probably just about attach his board directly to the SC-3000 by attaching the appropriate sized connector to the end to connect where the daughterboard does and adding a 5v feed. His wires are

Yellow: Video from expansion module
White: Audio
Orange: +5V power
Black: Ground for power and all signals
Red: Red (difference) signal
Blue: Blue (difference) signal
Green: Luma signal

and from the schematic the SC-3000 connector has
1: R-Y
2: B-Y
3: Y
4: GND
5: GND
6: COMP
7: RF
8: +9v

Edit - Ah - you would also have to add the audio feed, or take that off the existing composite output video connector. That would require another solder point, so maybe we just tell people to use the existing video connector for the audio.

Edit - does anyone know if that is a standard connector type used for the SC-3000 daughterboard? I haven't tried to find a compatible plug-in replacement yet.

I wonder if you can still buy these Coleco mod boards? If nothing else it would be interesting to see an original one. I just did a quick search and I couldn't find any obvious sign they are still for sale.

Yes, re end-user installation...agree, think 4095 board connector is still best idea - maybe run a short flat ribbon cable out a vent hole? Or, sneak it through the case between keyboard and front top cover?

I think the easiest for a plug-in removable mod would be the venting grills on the bottom half of the case. You wouldn't be able to see the cuts from the top and you don't have to remove any existing plugs at the rear of the case. You could just about cut the venting grills then slide one of the 8 pin plastic connectors with wires through there and plug in to the SC-3000 motherboard.



and here are the existing connectors from the rear - not much room to cut holes there

[5-11under]

Here's one of the links I recall seeing a couple of years back when I first looked around for hints on how to do this. Component video board installation guide for the Colecovision. I *think* this one was designed around the TMS9928A (see comments in the atariage thread)

I only have NTSC consoles. I'm running directly off of the TMS9928A's pins 35, 36, and 38. I'm guessing this would work just as well from a TMS9929A.

http://www.atariage.com/forums/topic/15 ... ecovision/

and here is the installation guide

http://www.colecovision.dk/Tools/CV-YPb ... all-02.pdf

It is a nice little package and not dissimilar to some of the packaging ideas we discussed earlier in the thread. Interesting idea leaving the potentiometers as user adjustable. That sounds like a sure way for an end user to stuff it up But it has a good section on how to tune the board and the optional video test pattern PCB is an interesting idea too.

The other lesson from this is that a plug in replacement daughter board would be way more usable for most people than having to solder multiple wires. The process in that installation guide is going to scare off a lot of people.

Just throwing it out there for ideas.

Cheers

Hi all, I've received a couple of e-mails from some members here, so I thought I'd join up to respond and join in the conversation.

Thia ColecoVision component/YPbPr mod kit is mine. It hasn't been too popular (which is fine, by the way - I was happy enough to have a good solution for myself), I think because it's a kit, and this scares off quite a few people. It sounds like the SC-3000 uses a daughtercard for video, so this may make the installation easier and therefore more accessible.

I should mention that there's another option, the F18A, an FPGA based VGA output to replace the TMS9918A, etc. This should work fine as long as your VGA monitor can handle 640x480 at 60 Hz.:
http://www.atariage.com/forums/topic/168968-f18a/
http://codehackcreate.com/archives/30

The first thing I did to try to get component video output out of a ColecoVision (TMS9928A) was send each of the three signals out from the TMS9928A to a buffer amplifer (no extra gain), and then off to a TV's component input. The picture was clear, but the blues were way too bright. If you're not familiar with YPbPr, this would be a good point to look it up in Wikipedia or something like that. Anyway, the 3 required signals are Y (green cable) which is the luminance signal (and sync), Pb which is blue minus Y, and Pr which is red minus Y. With the blue too bright, I turned down the Pb (B-Y) signal to compensate. Unfortunately, this not only turned down the B of B-Y, but it also turned down the "-Y". By subtracting some Y from the B-Y signal, I was able to get a signal that worked much better. I did the same procedure to the R-Y signal, but the change required for that signal is minimal. Some additional explanation is here: http://www.atariage.com/forums/topic/15 ... try1852923

A few more details to those interested in pursuing this further. I used the SOIC version of an LMH6644 as the buffer chip, although many other chips would be fine. Just make sure the bandwidth is suitable for video applications. My kit requires adjustment depending on what TV is connected. Ideally this shouldn't be the case. If I were to redo the circuit, I'd spend more time getting it more consistent. I'm guessing it's my design that is at fault, because DVD players and the like do not have this same issue. By the way, my kit is currently sold out, with more units hopefully available hopefully within a few weeks or so (no promises, though!). Sorry, it looks like my first post here is a bit of a sales post! I should note that my solution hasn't been tested with a PAL unit, as far as I know. It should work, though, although there may be subtle differences that need to be addressed.

Feel free to ask any questions, and I'll help out where I can.

[natshaw]

Hi there, 5-11under, thanks for that info. Yes, seems like we're on very similar track. One question though - what was the need for the buffer chip, and could you just have used (more) op-amps instead? My most basic plan was just to use op-amps in unity gain circuit as my buffer amplifiers. I didn't think a buffer chip was needed - or did you just find that easier?

Cheers!

[honestbob]

Hi 5-11under. Thanks for joining in the conversation.

I had a question about the need for an external clock source. The SC-3000 video daughterboard has a 4.43MHz crystal oscillator on it. From skim-reading through the original TMS99XXA docs, it seems that the Y channel already has horizontal and vertical sync signals built in. So I'm not sure why the external oscillator was required there. But if it was required, then I assume it was only required for PAL composite video, and isn't relevant for this component video mod. Does that sound right? Or do we still need an external clock source in there?

On page 3-6 of the TMS99XXA manual there is a high level diagram of a TMS9928A/29A connecting to a PAL or NTSC composite encoder with its own 4.43MHz crystal.

http://www.sc3000-multicart.com/images/ ... erface.png

By subtracting some Y from the B-Y signal, I was able to get a signal that worked much better.

Sorry - silly question time as I'm just trying to do the background reading necessary to understand this. So are you using a differential amplifier circuit something like in the link below to subtract some Y from the B-Y signal? Where do you connect your potentiometer in that diagram to control the amount of Y subtracted? Is it the R1 / R2 feed where the Y signal comes into the differential amplifier circuit?

http://www.electronics-tutorials.ws/opamp/opamp_5.html

[natshaw]

Honestbob, no xtal needed, Y already has both syncs.

[kerrjnr]

Despite understanding almost none of the technical details, I'm watching your progress with much interest as there isn't much I'd like more than to plug my beloved SC-3000H into a modern display - via a replaced 5-pin socket instead of an unseemly vent-ribbon if possible

[honestbob]

Despite understanding almost none of the technical details, I'm watching your progress with much interest as there isn't much I'd like more than to plug my beloved SC-3000H into a modern display - via a replaced 5-pin socket instead of an unseemly vent-ribbon if possible

Yes, I agree that is the neatest option. But it complicates the installation significantly. The advantage of poking a cable out a vent then having a little self contained plug box or similar (if that works) is that you don't need much in the way of soldering skills. I am hoping that it will be a simple plug in / out replacement for the video daughterboard with one relatively simple solder point for a 5v feed to the component board. We can then hide all of that in an external plug box with a single shrink-wrapped wire going to the case interior, or something like that.

The alternative is to desolder the existing 5 pin DIN, mount an 8 pin DIN in its place, probably make several cuts to traces on the motherboard, and solder another 3 wires from the component board to the new 8 pin DIN on the motherboard. You could still do this with the approach I'm suggesting. You would just hide the plug box inside the SC-3000 case (assuming there is enough room), and run connections to a new 8 pin DIN on the motherboard. Then you would make up your own custom cable to go to the TV. But that is probably enough to scare off a number of people who might give it a go with simpler installation instructions.

Anyway, the first step is to get something going I've finally had time to do a little background reading on op amps and read through more of 5-11under's notes in various forums, so I'll try to order in a couple of bits and pieces and see if I can get it working with my TV. Then natshaw and I can swap notes on what works and what doesn't. I'll get that replacement TMS9929A VDP and the other chips in the post tomorrow - forgot about it today, sorry.

Cheers

[natshaw]

One comment first: composite video from the 5-pin din, without any mods, into my LCD TV, actually gives a good picture. Suggest anyone following this try that first and see if happy.

Anyway, I've progressed a bit, which will also shed some light on other approaches.

I now have a stable, slighty dark, monochrome image on my Sony TV.

Pin 3 of daughterboard, to a 470 ohm resistor, to green (luminance + sync) socket on component video (DVD) input.

This gives about correct impedance for the VDP chip to drive. However, signal is not 1 V p-p, it's more like 0.25 V. Quality device like Sony TV can just understand signal. Dell monitor with component inputs cannot.

Using a buffer with selectable fixed 2x or 4x gain is obviously an attractive option, then opamps for colour correction. Building a non-inverting opamp with correct gains and presenting correct impedance to VDP is fiddly, but probably doable. Care must be taken to ensure any pots do not mess with impedance presented to VDP.

[arjoll]

Building a non-inverting opamp with correct gains and presenting correct impedance to VDP is fiddly, but probably doable. Care must be taken to ensure any pots do not mess with impedance presented to VDP.

Just put the pot in the feedback loop to control the gain. The impedance presented to the input should be constant.

[natshaw]

First thing I'll do is build a simple non-inverting 3x gain amp for the Y signal. Will test 2 things with that output signal:

• That it is still viewable on my not-fussy TV (i.e. I haven't gone backwards!)
• That it is now viewable on my fussy monitor (i.e. that I have made progress)

This should do it, any op-amp rated 4 MHz or more should be fine.

R1 (540~560) presents about the load that VDP would usually see on a Sega 4095 video daughterboard (R103 is 270 ohms + R104 is 270 ohms = 540 on that board). Input impedance of opamp is in parallel with R1, but is massive, so no issues there, won't factor that in! Output impedance of the opamp is very low, so this should work a treat!

Tests OK in a SPICE simulator, did get some bottoming-out (bottom clipping? what's the term?) when I increased the input signal amplitude, so will check that 1st if I don't get a working signal.

Could do this with transistors, will look into that once I get this going, may be able to steal them off the 4095 board! That would drop costs a lot for those willing to hack & chop.

8-pin DIN is what I'm going to use, especially since the Yeno models already have it fitted. For the PAL model, I'm just using unused pin for my Y-signal, but I need to also do the red & blue lines, so that approach won't last...

[honestbob]

Thanks for the circuit diagram - very helpful for matching against what I think I understand from my opamp reading I'm planning to scattergun a couple of types of op amps and video buffers off eBay based on what other people have tried (and which are relatively cheap to buy) and get some SOIC to DIP sockets for breadboard testing. I'll go post your ICs now - should be there in a couple of days.

For the PAL model, I'm just using unused pin for my Y-signal, but I need to also do the red & blue lines, so that approach won't last...

I was thinking about it. You can still use the 5 pin DIN plug on the PAL units. You would end up with something like:

5 pin video DIN connector
pin 1 - audio
pin 2 - Pb (cut the composite video connection)
pin 3 - Pr (cut the GND connection)
pin 4 - Y (cut the GND connection)
pin 5 - GND

You only need a single ground feed. When you make up a custom component to 5 pin DIN cable, you just twist the ground shields of all the wires together and solder to pin 5.

Also, instead of cutting the composite video connection to pin 2 it *may* be feasible to wire your Pb feed to pin 6 on the daughterboard connector if that has a direct connection to pin 2 on the 5 pin video connector.

[Carcenomy]

How about removing the DIN connector, cutting the legs and soldering the component signal cables to the pins you need instead? Saves cutting the PCB - they still make through-hole 5-pin DIN connectors, they don't still make SC-3000 mainboards.

[natshaw]

I will test initially with a CA3140 op-amp, I have a bunch of these from Jaycar. They store them on foil/polystyrene and don't care if the legs miss the foil, and they don't use static bags nor straps, so I just pray the bl**dy things still work. God, that company is useless, brain-dead, and a ripoff. Do they sell anything that's not junk? Their employees hate the interruptions that are customers, they just chit chat to each other all day - must be no managers on duty.

My circuit sim shows the 4MHz-rated CA3140 have slew rate issues over a couple Mhz, resulting in poor gain - is that how opamps are rated - max Mhz is only for unity gain? I might have to go for the big brother 15MHz CA3130, or something else, feels overkill, I guess I need at least double the 3.58 Mhz pixel rate.

[natshaw]

How about physical mods only - no electrical mods whatsoever? Since I'm happy the circuit will just be a plug & play into the internal video board connector...

I reckon 3 (or 4 incl. audio) RCA panel-mount sockets might be cool - would they fit on the left side of the Sega? Don't have mine handy.

One of these:


or a few of these:


Here:

[Carcenomy]

Hmmm, would work but would be a little frustrating for playing games - the component cable would foul the joystick cables. Plus it'd look a little rude having the RCA connectors poking out like sores from the side of the chassis

Actually I just realized something else - what's the SC-3000's schtick for getting audio out of it when you're not using RF?