TMS-RGB vs 'Hans Otten' PCB

بواسطة Rataplan

Champion (354)

صورة Rataplan

14-05-2023, 15:05

Hi. I'm looking to RGB mod my ColecoVision. Same VDP as MSX as we know. Now, would there be a noticable difference between https://videogameperfection.com/products/tms-rgb-v2-board/ and the pcb at https://download.file-hunter.com/Technical/Hans%20Otten/rgbm... which I can make very cheaply? Anyone tried either one?

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بواسطة CASDuino

Champion (358)

صورة CASDuino

14-05-2023, 17:30

I have the TMS-RGB installed in my Toshiba HX-10 and it really is amazing. The picture quality is beautiful.

بواسطة sdsnatcher73

Enlighted (4295)

صورة sdsnatcher73

14-05-2023, 19:06

A similar method to create RGB is present in some MSX1 computers. I’m the Netherlands the Sony HB-75P and JVC HC-7GB has such circuit. Whilst on this machine you do get RGB the quality of the RGB cannot compare to what we are seeing on machines with V9938 or V9958. Hans’s schematic allows for tuning the individual colors so it might get better results but it is hard to predict without building the board. As you said it will be cheap to build so don’t expect miracles, then again it won’t cost you an arm and a leg you try it out…

بواسطة Rataplan

Champion (354)

صورة Rataplan

14-05-2023, 20:09

Yeah nor does the TMS-RGB really, but still it's like 5 euros tops and some time vs almost 50. The tinkerer in me says try the home-made one first. But I've seen TMS-RGB in real life on a MSX1 and that's absolutely awesome. So i was just wondering whether someone actalually has both or at least the home made one, to compare.
Thanks for your insights so far Smile

بواسطة sdsnatcher73

Enlighted (4295)

صورة sdsnatcher73

14-05-2023, 19:21

One issue that I suspect will happen with this schematic is jail bars. The sync output is derived directly from the Y signal so it is not a clean CSYNC. This also is visible in the 2 computers mentioned.

بواسطة Rataplan

Champion (354)

صورة Rataplan

14-05-2023, 20:15

But what does the TMS-RGB do? It taps from the same signals. I've not looked up the chips on it, but it's just some glue logic I suppose? But yeah.. I guess it's gonna be the TMS-RGB. The mod will be more expensive than the console itself Question I was playing HERO on both my MSX2 (with native RGB) and my composite ColecoVision, next to eqch other. Composite on the CV is already miles better than the native RF of course. But still it's amazing how crisp the MSX is in comparison. Ah well Smile

بواسطة cjs

Master (143)

صورة cjs

15-05-2023, 03:21

sdsnatcher73 wrote:

One issue that I suspect will happen with this schematic is jail bars. The sync output is derived directly from the Y signal so it is not a clean CSYNC. This also is visible in the 2 computers mentioned.

Is that due to the way the VDC works, or something to do with the technique used for that converter?

On computers without composite sync (such as my FM-7, where the RGB connector has just separate hsync/vsync) I regularly plug the (monochrome) composite video output into the external sync input of my Sony PVM, and I don't recall seeing jailbars when I did that.

بواسطة sdsnatcher73

Enlighted (4295)

صورة sdsnatcher73

16-05-2023, 12:23

Well the jail bars may be less obvious on CRT and especially on professional CRT (PVM may even strip sync from the composite signal). Also FM-7 has digital RGB FDD so that needs to be converted to analog before hooking up to a PVM (unless your PVM has digital input, but European models don’t AFAIK). Later FM77 models do have analog RGB.

بواسطة cjs

Master (143)

صورة cjs

16-05-2023, 14:06

sdsnatcher73 wrote:

Well the jail bars may be less obvious on CRT and especially on professional CRT....

Why would that be?

Quote:

(PVM may even strip sync from the composite signal).

Well, of course, as all displays must. Pretty much every display is going to need separate horizontal and vertical sync signals internally, so the internal circuitry will be separating them. It's not too hard when doing that just to ignore a luma signal mixed in with the sync.

The same often goes for RGB, too. All CRTs and LCD displays (as far as I'm aware) need separate R, G and B luminance signals to drive the tube guns or the pixel matrix, and so a composite or Y/C input will have to be converted to RGB for that purpose. This is why you can mod so many consumer TVs to have an RGB input.

Quote:

Also FM-7 has digital RGB FDD so that needs to be converted to analog before hooking up to a PVM (unless your PVM has digital input...

Not actually; the only thing you need is a display that doesn't get upset when you give it 5 V on its inputs, which my PVM does not. (It of course does drive the three luminance signals to maximum brightness, but that's more or less what you want anyway.) That said, yes, I do use a DRGB converter board that brings the levels down to, I think about 1 V P-P. (IIRC, I tried it at the 0.7 V P-P from the monitor's spec sheet but it didn't work so well. But I could be wrong; I've not measured the current settings of the pots on my board.)

But I decided to look around to find out what usually causes jail bars, which took me down a bit of a rabbit hole, including this forum thread and this excellent video. The source of everything there can be summed up as "interference affecting the chroma signal," which makes perfect sense: chroma is by far the highest frequency signal involved (several octaves higher than luma) and also of lower amplitude than the luma, so it's likely to suffer most from any distortion. The grounding fix near the end of that video ("Fourth change") produced a particularly impressive improvement.

But RGB doesn't have a chroma signal, just three separate luma signals, so none of the sources of interference mentioned in the posts and video above appear to be relevant. Are you saying that the jailbars are related to the Y/R-Y/B-Y to R/G/B conversion in some way? What would be the source of the issue, and how would you change the circuit to clean it up?