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Only B&W RGB on a NTSC 99/4a with TMS-RGB (but with PAL VDP)


Lambda Mikel

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Hello all,

 

so my new-revision NTSC motherboard got the TMS-RGB, and the VDP was changed for PAL (->TMS 99929A). However, RGB image was black & white only. Please see pictures attached. We also cut wires L2 / L3 near the video DIN socket, but that made no difference (well, composite output was gone from the DIN then).

 

What other mods might be required to an NTSC new-revision motherboard in order to get color? The monitor is fine and works perfectly - and in color - with other RGBs sources (e.g., Amiga 500, Amstrad CPC).

 

Also, I am noticing that the audio is a bit faint and noisy now with that board. This might be unrelated to my failed TMS-RGB installation attempt, but I hadn't noticed this until I put the machine back together. I removed the TMS-RGB for now and put in the NTSC VDP. Color is back.

 

Thanks for any ideas.

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Edited by Lambda Mikel
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8 hours ago, Lambda Mikel said:

Sorted, can be closed. Used an old-style motherboard and applied the TI mod. Without applying this mod, you'll only be getting B&W from an NTSC 99/4a. Simply swapping the VDP and installing TMS-RGB doesn't do it.

 

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thanks for this, added to the FAQ, prob you could have used the NTSC version of the chip (9928) to avoid the mod

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1 hour ago, arcadeshopper said:

thanks for this, added to the FAQ, prob you could have used the NTSC version of the chip (9928) to avoid the mod

I don't think so. The TMS-RGB didn't work with the NTSC VDP for me. Showed garbage on RGB. Also I wanted a PAL TI. So, one can leave the NTSC 5pin DIN installed, but the audio is buzzing. Now, I also needed to route another audio cable. That solved the buzzing and noise issue. Maybe interference from the video or insufficiently shielded cable? I have a 4 RCA socket to DIN5 cable (same I usr for C64 etc.) And was only going to use only the audio line but the video buzzing was very audible. Yes, I used the right line of the cable ? Dedicated mini stereo socket fixed the audio.

Edited by Lambda Mikel
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5 hours ago, Lambda Mikel said:

I don't think so. The TMS-RGB didn't work with the NTSC VDP for me. Showed garbage on RGB. Also I wanted a PAL TI. So, one can leave the NTSC 5pin DIN installed, but the audio is buzzing. Now, I also needed to route another audio cable. That solved the buzzing and noise issue. Maybe interference from the video or insufficiently shielded cable? I have a 4 RCA socket to DIN5 cable (same I usr for C64 etc.) And was only going to use only the audio line but the video buzzing was very audible. Yes, I used the right line of the cable ? Dedicated mini stereo socket fixed the audio.

the 9918a?  or 28a?  the console originally had an 18.. composite.. 

https://en.wikipedia.org/wiki/Texas_Instruments_TMS9918#TMS9918A_and_TMS9928A

 

Edited by arcadeshopper
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Both the beige and the silver had an 18 installed. I checked TMS-RGB first with the 18 in the beige 99er, and got RGB video garbage. Plugged in the 28A and got B&W RGB. Then found the mod, but didn't apply it as it seemed to apply to the black&silver old revision board. I hence reverted the beige into original NTSC condition, and modded the silver TI with the old style board instead. I haven't checked NTSC VDP (18) with TMS-RGB in this one, as it already had failed in the beige with the same 18 NTSC VDP. Hence, I went straight for PAL 28a. Discovered that it was B&W. Applied the TI mod. Got color. Happy :D

 

I didn't unsolder the DIN socket if I ever want to revert it back to original NTSC, it's easy to do. I added RGB DIN 6 socket for Amstrad CTM RGBs monitor, and an extra mini stereo to fix the audio droning.

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