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Falonn

TMS-RGB: An RGB Mod for 2020 and Beyond

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(TI-99/4A) Yes, the VDP provides the audio clock. I've run a console with the 9918A replaced with a 9928A before. I don't remember if I tested sound, but everything else worked.

 

If you are getting the title page, you can be certain that the VDP, VDP RAM, scratchpad RAM and GROMs are working. Color would be a function of the video output. If you just plugged the chip directly into the motherboard, and it's a US console, then yeah, you're only getting the luma output, thus, black and white. There's no circuitry on the US motherboard that will support the 9928 directly, not even with jumpers. In fact you are wiring one of your video out pins to the console reset bus. You'll need to lift the three video out pins and wire them to the mod board manually.

 

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26 minutes ago, Tursi said:

(TI-99/4A) Yes, the VDP provides the audio clock. I've run a console with the 9918A replaced with a 9928A before. I don't remember if I tested sound, but everything else worked.

 

If you are getting the title page, you can be certain that the VDP, VDP RAM, scratchpad RAM and GROMs are working. Color would be a function of the video output. If you just plugged the chip directly into the motherboard, and it's a US console, then yeah, you're only getting the luma output, thus, black and white. There's no circuitry on the US motherboard that will support the 9928 directly, not even with jumpers. In fact you are wiring one of your video out pins to the console reset bus. You'll need to lift the three video out pins and wire them to the mod board manually.

 

It's good to have someone with actual experience here.

The setup that Retro is attempting has the board soldered directly to the bottom of the 9928 in place of the 9918.  From the schematics, it appears that jumpers on W201, W203, and W206 will provide the load resistors that it needs.  Jumpers W202 and W204 should be removed.  This would effectively hook up YPbPr to the standard video output connector.

 

The schematic shows a small length of coax that goes from pin 38 to the audio chip.  That should be removed, and W101 should be jumpered instead. Then the audio chip needs to be a replaced with a SN94624 or SN76494 to use the slower clock.

Then the add-on board is connected to its own video output.

 

Are you saying that's still not good enough?

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TMS-RGB will not work on either of the SG-1000 MK II systems I have. One has a TMS-9918, the other has a Sega custom chip. Luckily it was easy enough to mod the system for composite video, which was my initial goal.

I will be trying to install one into a Dick Smith Wizzard next, which does have a TMS-9929, I believe.

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14 hours ago, cdoty said:

TMS-RGB will not work on either of the SG-1000 MK II systems I have. One has a TMS-9918, the other has a Sega custom chip. Luckily it was easy enough to mod the system for composite video, which was my initial goal.

I will be trying to install one into a Dick Smith Wizzard next, which does have a TMS-9929, I believe.

The SG-1000 II with the custom Sega chip can be easily modded for RGB by using an amplifier circuit or even a Genesis Triple Bypass board.

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35 minutes ago, ApolloBoy said:

The SG-1000 II with the custom Sega chip can be easily modded for RGB by using an amplifier circuit or even a Genesis Triple Bypass board.

Yep, the RGB and CSync points are labeled on the board.

I was just after a composite signal, and audio, I found those also.

Edited by cdoty

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How can i get the miniboard for mounting the 9-pin mini din socket? I didn't found the gerbers files in the repository, any suggestions? 

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The ones I used were from Ospark I believe.

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2 minutes ago, -^CrossBow^- said:

The ones I used were from Ospark I believe.

Thanks, I'll look there! 

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The links are a little buried on the tms-rgb.com site, sorry.  On the BOM page, there are a pair of "this breakout board" links that take you to the relevant OSHPark project pages for the 8-pin and 9-pin breakouts.

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6 hours ago, Falonn said:

The links are a little buried on the tms-rgb.com site, sorry.  On the BOM page, there are a pair of "this breakout board" links that take you to the relevant OSHPark project pages for the 8-pin and 9-pin breakouts.

Yes, i missed the link! found it and just ordered some, thank you!

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I also want to say that I installed mine recently on my good CV and the output looks great through an OSSC, although there is a touch of noise. I can easily mask it using the OSSC's LPF but I still need to try this on my PVM. It's also worth noting that mine has a Yurkie AV mod installed (added by a previous modder, maybe by Yurkie himself?) but I don't think that's the cause of the video noise. 

 

After this I might be interested in pairing the TMS-RGB with an internal RGB to component converter, as I have another CV which has a crude component video mod (just straight from the video output pins with pull-down resistors and decoupling caps) that only seems to work properly on my PVM.

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28 minutes ago, ApolloBoy said:

After this I might be interested in pairing the TMS-RGB with an internal RGB to component converter, as I have another CV which has a crude component video mod (just straight from the video output pins with pull-down resistors and decoupling caps) that only seems to work properly on my PVM.

You may want to hang fire on that.  The TMS-RGB actually generates component signals before it then converts them to RGB.  Falonn has kindly agreed to help guide me with cutting his TMS-RGB schematic down to a component only output design which I then plan to create a PCB design for.  Only downside is that this may be a few months away as we're working on another project at the moment which needs to be completed first.

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1 minute ago, Ikrananka said:

You may want to hang fire on that.  The TMS-RGB actually generates component signals before it then converts them to RGB.  Falonn has kindly agreed to help guide me with cutting his TMS-RGB schematic down to a component only output design which I then plan to create a PCB design for.  Only downside is that this may be a few months away as we're working on another project at the moment which needs to be completed first.

Interesting. I don't mind waiting a few months really, my other CV is in storage and I'm satisfied enough with the RGB output on my good system that this isn't a priority.

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1 minute ago, ApolloBoy said:

Interesting. I don't mind waiting a few months really, my other CV is in storage and I'm satisfied enough with the RGB output on my good system that this isn't a priority.

We'll no doubt post something in this thread when progress is made.

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On 8/24/2020 at 1:45 PM, ChildOfCv said:

The schematic shows a small length of coax that goes from pin 38 to the audio chip.  That should be removed, and W101 should be jumpered instead. Then the audio chip needs to be a replaced with a SN94624 or SN76494 to use the slower clock.

Yeah, I actually took deeper examination of his issue to the thread he started in the TI forum. ;) That said, be careful with the schematic - the commonly available schematic is for the the 99/4 rather than the 4A, and the clocking is a little different (as far as I remember, I need to get my TI's here to verify that my old memory is still on track.)

 

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5 minutes ago, Tursi said:

Yeah, I actually took deeper examination of his issue to the thread he started in the TI forum. ;) That said, be careful with the schematic - the commonly available schematic is for the the 99/4 rather than the 4A, and the clocking is a little different (as far as I remember, I need to get my TI's here to verify that my old memory is still on track.)

 

The attached may help - it's specifically for the 4A and includes the schematics.

ti99_tech.pdf

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4 hours ago, Ikrananka said:

The attached may help - it's specifically for the 4A and includes the schematics.

Wow, that's super clean, I didn't have that. When the heck did Mainbyte post that one? ;)

 

Thanks!

 

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10 hours ago, Ikrananka said:

The attached may help - it's specifically for the 4A and includes the schematics.

That's the same link I included 25 posts ago, back on page 3! :lol:

 

Though, like ChildOfCv noticed, be careful scrolling through it too fast: it contains two sets of schematics, one for the 99/4A and another for the 99/4QI... whatever that is.

 

11 hours ago, ApolloBoy said:

After this I might be interested in pairing the TMS-RGB with an internal RGB to component converter...

Yeah, like Ikrananka was saying, this would be a roundabout, inefficient path.  The output signal is almost natively component.  So you'd be going component'ish --> RGB --> component, where at least that first step (through the LMH1251) sucks up a lot of power.  A component-only board would only require half the parts, half the power, potentially half the PCB size (or possibly double the component size to make it easier to solder by hand?), and less than half the cost because it wouldn't need the expensive LMH1251 anymore.

 

I'm not sure how useful a component version would be to the wider community, seeing as most new TVs are dropping component inputs completely.  But, after that laundry list of benefits above and knowing that it's just TMS-RGB with a few things removed, I'm interested now just out of completeness.

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Interesting, the hand-drawn version mentions a TMS9318A for the VDP with a hastily corrected "9929A" written above it.  Maybe they were planning to use some future VDP product that never materialized?  And designing it for both styles of output explains why all the jumpers are there for choosing between composite and component'ish output.

 

It also looks like the hand-drawn schematic must have been the source of the SGCCK vs. SGC CLK naming discrepancy on either side of W104.  The same names are used on the same pages in the same places as the other PDF.

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20 hours ago, ApolloBoy said:

I also want to say that I installed mine recently on my good CV and the output looks great through an OSSC, although there is a touch of noise. I can easily mask it using the OSSC's LPF but I still need to try this on my PVM. It's also worth noting that mine has a Yurkie AV mod installed (added by a previous modder, maybe by Yurkie himself?) but I don't think that's the cause of the video noise. 

 

After this I might be interested in pairing the TMS-RGB with an internal RGB to component converter, as I have another CV which has a crude component video mod (just straight from the video output pins with pull-down resistors and decoupling caps) that only seems to work properly on my PVM.

I have slight jail bars noticeable on mine that is especially evident on solid background colors like blues, greys... Was told that others who tested with the OSSC saw the same and had to modify some of the settings on the OSSC to get rid of them and saved that as a dedicated profile. I've not messed with it because it honestly doesn't bother me when playing games and I only noticed it when I popped in Fathom as it is there but didn't show up in my pics. Or on the player/difficulty select menus at the start of games.

 

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For what it's worth, I saw this all through development, too.  The Framemeister is razor sharp with zero noise.  I always saw faint jailbars through the OSSC when against a black background.  But making the offset changes in step #10 of the install guide cleaned it up.  All that's left on the OSSC afterward is a very tiny bit of overshoot in rare cases.  (The Framemeister is also able to clean that up somehow, too, leaving emulator-like, essentially perfect output.)

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On 8/27/2020 at 4:50 AM, Falonn said:

That's the same link I included 25 posts ago, back on page 3! :lol:

Though, like ChildOfCv noticed, be careful scrolling through it too fast: it contains two sets of schematics, one for the 99/4A and another for the 99/4QI... whatever that is.

Hehe, sorry, I jumped into the middle of the thread. ;)

 

The QI was the last release of the TI99 - consolidated some discrete logic and supposedly improved the quality (QI = Quality Improved). They're generally less common and less desirable to most people. ;)

 

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