MSX1 RGB mod

[Midori]

I traded an Atari for a MSX last year. However the YUV converter in it was broken so I only got a black-and-white image from it, not that big a loss though since it was composite only anyway. However I did want to be able to use the thing. Of course it worked somewhat by connecting the computer to my TVs component input, but that was not optimal since the colours were off and I found no suitable amp for it.

So I searched and found a translated dutch pdf with instructions on how to build a YUV to RGB circut for an MSX. I was bored and decided to give it a go despite that I found no people reporting results from building it.

The pdf is available here: http://www.msxarchive.nl/pub/msx/mirrors/hanso/hwdoityourself/rgbmsx1.pdf

After four hours, I have produced this:



The little board looks a lot more simple than it was for me to build :-) The top looks better than the bottom...



Fairly ugly and those pots will have a more worthy life one day. But I didn't feel like spending time trying to tidy up something I didn't even know if it worked :-)

Did it work? I'll let this image speak for me:



In other words, it sure does :-) I'm having a little interference in the image and such but that is probably because I spent less love on the thing than I should have. Will be nice to it from now on. The image is good otherwise, very strong colours and accurate. I was actually fairly surprised.

But here we are, one working RGB circut for the TMS 9928 and 9929. Should be useful for other machines aswell that uses that chip.



Darn shame that the machine runs in 50 Hz though, poor Knightmares music is tormented over and over...

[l_oliveira]

You need an 60hz VDP chip (TMS9928 for YUV and TMS9918 for NTSC CVBS) by the look of the things you have an TMS9929 on the computer. Also editing the ROM header bit to show 60hz so games choose the appropriate timing do help. I have spares here if you need (and are willing to pay the shipping)

If you want to you could make it into an MSX2 easily by adding the V9938 chip and RAMs. I also have spares of the V9938 here.

[Midori]

Yeah, there's a TMS9929 in the computer.

Thanks for the offers :-) I did order two 9929s from a strange site already though, will see if they arrive...

But you do need to do a little more than add a V9938 to make a MSX2 don't you? Except the RAM. I seem to recall more stuff... Interesting offer though. Of course I would pay for the things :-)

[l_oliveira]

With hacked system ROMs all you need is the E-VDP chip (V9938) and it's 128 KB DRAM. Since it's I/O logic is basically the same as the original one on the MSX for TMS9918, it's just an drop-in replacement.

For a "real" MSX2 upgrade with non hacked ROMs you need also the RTC/backup ram/battery circuit. 64KB RAM is the minimal MSX2 system configuration. You would have to give up one external slot connector for the "sub" rom with the extended bios, though. So most MSX2 systems contain an "slot expander" circuit installed on the primary slot 3 to allow 3 more internal sub slots for adding for example an bonus software (such an text editor or demonstration program)

If the MSX contains an "CHIP-ENGINE" such as the S-3527 Yamaha chip you can use it's internal slot expander logic to add the "SUB-ROM" without lose an external slot.  Considering the picture (It appears to be an small Mitsubishi unit) it's very likely to be using an chip-engine.

[Midori]

Oh, never heard of that.

I have a Mitsubishi unit, yes. A ML-F80 to be specific. It has 64 KB RAM. Not sure if it has a Chip engine though. No Yamaha chips in it. The only two that stand out except the CPU and sound-chip is the Hitachi HN613256P(MSX-Basic and bios?) and the Mitsubishi chip called M5L8255AP-5.

[l_oliveira]

If it's not chip-engine based it will have a lot of TTLs and an i8255 (or equivalent, in your case an Mitsubishi part) an AY3-8910 and the TMS9928 chip. Along with an Z-80A.

The chip engine purpose is integrate at least all the TTLs, the PPI (8255) and PSG (AY-3-8910, the same sound processor G.I. developed for it's/Mattel's Intelivison design.)

[Midori]

There's an army of chips in this unit. An overview pic here :-)



I recieved a TMS9928 this monday, I managed to install it in my computer:



I also took some time to improve the RGB circut:



Now it works a bit better, and it runs i glorious 60 Hz :-)



The image is flawed though. There is quite a bit of interference in the colour signals, and it is a bit bright. So there is a lot to improve.

But if you toy around a bit with the contrast and brightness settings on the TV the image sure is decent, just that it could be better :-) Much better than before when mine only gave a poor greyscale image ;-)

[l_oliveira]

Looking awesome !

I look forward for the schematics of the YUV to RGB  converter circuit once it's done.

[Midori]

The schematic is available in the dutch pdf in the first post :-) My improvements are mainly trying to tidy up m circut and replacing wires with better ones.  And replacing the big potentimeters with trimpots.

I'm fairly annoyed by this interference though. It's in the colour signals, there is no interference in the Y signal used as sync. Perhaps I should replace some wires with shielded ones...

[Midori]

The colours just are not correct, so I have dug deeper. If found some new information, a new circut for RGB, this time from TI themselves.

Here is a pdf with everything: http://spatula-city.org/~im14u2c/vdp-99xx/e3/SPPA004A_9928-29_9118-28_Interface_to_Monitors.pdf

This seems serious and better than the dutch pdf. I worked on the schematic and produced this new one instead with just the DC restoration, RGB converter and the Sync separator:



I have already built the sync separator and DC restoration parts because I wanted to try them out with the dutch RGB converter. The results aren't that great though :-) The image is now mostly black and white, there is colour, but it's... something, probably too weak.

Will try to build the TI RGB converter aswell and see if that works better.

[Drakon]

what exactly is the type of image "flaws" do you get?  From the looks of your screenshot it looks very much like the distortion I get on my rgb nes.  And what exactly do you mean by "not correct" colours?  Are they not strong enough or the wrong colours?

[Midori]

The flaws are probably not the same as the ones in your NES. The flaws appear in such a way that depending on which colours are displayed the other colours purities are affected.

For example in Knightmare which I have a screensshot of here the black colour is pure black, but in antarctic adventure the black colour is wrong by being to bright and has blue lines mixed in it. I believe there is something wrong in the mixing circuit or that the signals are not clamped and therefore have no common reference level... Or I did something wrong :-)

I'm going to try a new circuit I found in a yamaha MSX computer service manual instead and see if that improves the image. The one I linked to from TI didn't work well at all. It gave me a black-and-white image :-) Perhaps I failed with that one to...

[Drakon]

yeah these certainly aren't simple circuits.  I've never seen hardware that outputs yuv by default