JJB Posted January 26, 2021 Share Posted January 26, 2021 Just confirming that TMS RGB works very well in my US TI after replacing the TMS9918A with a TMS9928A I purchased from Ebay. Pin 38 (CPUCLK) wasn't used for the sound processor so I just terminated it with a 560R resistor, same with pin 35 (EXTVDP). The composite video signal from pin 36 goes to a inductor (L202) first, I cut the incoming side and bent it out of the way. Right under that inductor is an unused wire link which can be conveniently used to terminate pin 36 with another 560R resistor. I re-used the existing TI video connector to provide RGB out and made a custom DIN - SCART cable to connect to a cheap RGB - HDMI converter. SCART needs a positive potential on pin 16 (Fast Switching) to select RGB instead of CVIDEO but with a 5-pin DIN I didn't have a spare pin to carry 5V from the console. I just opened up the converter and connected pin 16 internally to a suitable 5V point via a current-limiting resistor. Cheers, Jochen 7 Quote Link to comment Share on other sites More sharing options...
GDMike Posted January 26, 2021 Share Posted January 26, 2021 Photos? 1 Quote Link to comment Share on other sites More sharing options...
JJB Posted January 26, 2021 Author Share Posted January 26, 2021 6 Quote Link to comment Share on other sites More sharing options...
ti99iuc Posted January 26, 2021 Share Posted January 26, 2021 @JJB Really nice try! There is also this old TI doc that mention some steps to convert NTSC to PAL but I never tried to do ? 2 Quote Link to comment Share on other sites More sharing options...
RickyDean Posted January 26, 2021 Share Posted January 26, 2021 (edited) 17 hours ago, JJB said: Just confirming that TMS RGB works very well in my US TI after replacing the TMS9918A with a TMS9928A I purchased from Ebay. Pin 38 (CPUCLK) wasn't used for the sound processor so I just terminated it with a 560R resistor, same with pin 35 (EXTVDP). The composite video signal from pin 36 goes to a inductor (L202) first, I cut the incoming side and bent it out of the way. Right under that inductor is an unused wire link which can be conveniently used to terminate pin 36 with another 560R resistor. I re-used the existing TI video connector to provide RGB out and made a custom DIN - SCART cable to connect to a cheap RGB - HDMI converter. SCART needs a positive potential on pin 16 (Fast Switching) to select RGB instead of CVIDEO but with a 5-pin DIN I didn't have a spare pin to carry 5V from the console. I just opened up the converter and connected pin 16 internally to a suitable 5V point via a current-limiting resistor. Cheers, Jochen I have a tan TI, had it since about 92, that has a 9928 and a 6 pin din connector where the 5 pin din is supposed to be, I have a dijit rgb unit that plugs in. But can find no documentation for it, even asked here in the past. Edited January 26, 2021 by RickyDean spelling - thick fingers Quote Link to comment Share on other sites More sharing options...
JJB Posted January 28, 2021 Author Share Posted January 28, 2021 this one? http://www.mainbyte.com/ti99/hardware/peb/avpc.html Quote Link to comment Share on other sites More sharing options...
GDMike Posted January 28, 2021 Share Posted January 28, 2021 2 hours ago, JJB said: http://www.mainbyte.com/ti99/hardware/peb/avpc.htm http://www.mainbyte.com/ti99/hardware/peb/avpc.htm Quote Link to comment Share on other sites More sharing options...
RickyDean Posted January 28, 2021 Share Posted January 28, 2021 (edited) 12 hours ago, JJB said: this one? http://www.mainbyte.com/ti99/hardware/peb/avpc.html No, this was an external unit, plugged into the ti with a 6 pin DIN connector, has 4 cables coming out R,G,B, and audio. Was only meant to be 40 column rgb. I thought I posted a pic in the past, but doing a search, can't find it. Will have to locate the unit and take (again?). I saw a conversation in the search for dijit, between the Great Gazoo and Ksarul, where Gazoo was asking something about it. https://atariage.com/forums/topic/238138-original-dijit-video-card/?tab=comments#comment-3234632 Edited January 28, 2021 by RickyDean added content Quote Link to comment Share on other sites More sharing options...
JJB Posted February 6, 2021 Author Share Posted February 6, 2021 (edited) Apologies have to revise my story about AC-coupling the R-G-B signals, it did cause colour smearing in some cases. Fine-tuning the capacitor values would probably solve that but I decided to remove the electrolytics and live with a bit of colour diff; picture quality is still great. I had a problem with noise on the TMS-RGB sync line, causing my RGB->HDMI converter to re-sync and show that annoying OSD. Chased a lot of red herrings but can only conclude the noise is generated by TMS-RGB. With a scope and a capacitor decade box I determined that a 10nF capacitor between sync and ground nicely cleans up the signal and makes the converter behave. Hope that helps, Jochen Edited February 10, 2021 by JJB Removed AC-coupling; sync noise solution 2 Quote Link to comment Share on other sites More sharing options...
Calab Posted January 22, 2022 Share Posted January 22, 2022 On 1/25/2021 at 10:42 PM, JJB said: Just confirming that TMS RGB works very well in my US TI after replacing the TMS9918A with a TMS9928A I purchased from Ebay. Pin 38 (CPUCLK) wasn't used for the sound processor so I just terminated it with a 560R resistor, same with pin 35 (EXTVDP). The composite video signal from pin 36 goes to a inductor (L202) first, I cut the incoming side and bent it out of the way. Right under that inductor is an unused wire link which can be conveniently used to terminate pin 36 with another 560R resistor. I re-used the existing TI video connector to provide RGB out and made a custom DIN - SCART cable to connect to a cheap RGB - HDMI converter. SCART needs a positive potential on pin 16 (Fast Switching) to select RGB instead of CVIDEO but with a 5-pin DIN I didn't have a spare pin to carry 5V from the console. I just opened up the converter and connected pin 16 internally to a suitable 5V point via a current-limiting resistor. I have one of these TMSRGB boards that I was hoping to use in my QI TI-99/4a, but it has a TMS9918A chip. I want to connect the RGB output to a 15Khz capable VGA monitor, so SCART support isn't necessary. Could you provide a step by step of how you replaced the TMS9918A with a TMS9928A, please? Is is possible to retain the composite video output on the TI-99/4a with this mod? If not, how about component or S-Video output? 1 Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted January 24, 2022 Share Posted January 24, 2022 On 1/22/2022 at 11:37 AM, Calab said: Is is possible to retain the composite video output on the TI-99/4a with this mod? If not, how about component or S-Video output? No, the RGB becomes the output. The 9918 generated the composite on-chip, so replacing it with a 9928 would require you to add modulation circuitry to get composite back. On the good side, the modulation circuit wouldn't interfere with the RGB output so you'd have your choice of outputs. Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted January 24, 2022 Share Posted January 24, 2022 On 1/22/2022 at 1:37 PM, Calab said: If not, how about component or S-Video output? 7 hours ago, ChildOfCv said: The 9918 generated the composite on-chip, so replacing it with a 9928 would require you to add modulation circuitry to get composite back. FWIW, S-Video (Y/C) is a slightly different color space than the YPbPr output of the 9928A. Thus, to get S-Video from a 9928A-based TI you will need additional conversion circuitry, the mathematics of which are beyond my interest, or a specialized chip or two. A while back I tried the simple method of combining Pb+Pr to get C, but doing so failed to produce a color screen. Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted January 24, 2022 Share Posted January 24, 2022 1 hour ago, OLD CS1 said: FWIW, S-Video (Y/C) is a slightly different color space than the YPbPr output of the 9928A. Thus, to get S-Video from a 9928A-based TI you will need additional conversion circuitry, the mathematics of which are beyond my interest, or a specialized chip or two. A while back I tried the simple method of combining Pb+Pr to get C, but doing so failed to produce a color screen. It's not a color space issue. You need the modulator to turn it into a form that the TV expects. Pb and Pr are just voltage levels that track with the color output. The modulated signal is a 3.58MHz sine wave which gets phase shifted to the color in question and whose magnitude controls color saturation. The circuitry needed to convert this would include a LM1889 or MC1372 at its core. Quote Link to comment Share on other sites More sharing options...
Calab Posted February 5, 2022 Share Posted February 5, 2022 On 1/24/2022 at 7:58 AM, OLD CS1 said: FWIW, S-Video (Y/C) is a slightly different color space than the YPbPr output of the 9928A. Thus, to get S-Video from a 9928A-based TI you will need additional conversion circuitry, the mathematics of which are beyond my interest, or a specialized chip or two. A while back I tried the simple method of combining Pb+Pr to get C, but doing so failed to produce a color screen. But could you run wires from the YPbPr pins of the 9928A to RCA jacks and get component video? or do you need some buffer/amp circuitry between the chip and RCA jacks? Quote Link to comment Share on other sites More sharing options...
ChildOfCv Posted February 12, 2022 Share Posted February 12, 2022 It's best to have amplifiers on each output. The chip is not geared to directly drive a 75-ohm load. Quote Link to comment Share on other sites More sharing options...
RickyDean Posted November 27, 2023 Share Posted November 27, 2023 (edited) On 1/28/2021 at 11:45 AM, RickyDean said: No, this was an external unit, plugged into the ti with a 6 pin DIN connector, has 4 cables coming out R,G,B, and audio. Was only meant to be 40 column rgb. I thought I posted a pic in the past, but doing a search, can't find it. Will have to locate the unit and take (again?). I saw a conversation in the search for dijit, between the Great Gazoo and Ksarul, where Gazoo was asking something about it. https://atariage.com/forums/topic/238138-original-dijit-video-card/?tab=comments#comment-3234632 Found this thread tonight and found the DIJIT RGB interface last week. Anybody got a manual, info, something? Did find an ad in MicroPendium (2nd picture attached). Edited November 27, 2023 by RickyDean spelling, added content 1 Quote Link to comment Share on other sites More sharing options...
+Ksarul Posted November 27, 2023 Share Posted November 27, 2023 15 hours ago, RickyDean said: Found this thread tonight and found the DIJIT RGB interface last week. Anybody got a manual, info, something? Did find an ad in MicroPendium (2nd picture attached). I think that's the first one of these I've actually seen in the wild. . . Quote Link to comment Share on other sites More sharing options...
RickyDean Posted November 27, 2023 Share Posted November 27, 2023 (edited) 38 minutes ago, Ksarul said: I think that's the first one of these I've actually seen in the wild. . . Wow, I've got a piece of equipment that our Ksarul doesn't have, amazing!! Of course you may have several in the basement? Edited November 27, 2023 by RickyDean added content Quote Link to comment Share on other sites More sharing options...
+Ksarul Posted November 27, 2023 Share Posted November 27, 2023 30 minutes ago, RickyDean said: Wow, I've got a piece of equipment that our Ksarul doesn't have, amazing!! Of course you may have several in the basement? Nope, the cupboard is bare on this one. I'd read about these, but they were released while I was in Germany and were no longer available by the time I returned to the US. I've never seen one show up for sale either, so I still don't have one. I was eventually able to acquire an AVPC though, as they show up for sale once in a while (I had the same problem there, as they went on sale and then were no longer available by the time I initially went looking for one). Quote Link to comment Share on other sites More sharing options...
RickyDean Posted November 27, 2023 Share Posted November 27, 2023 3 minutes ago, Ksarul said: Nope, the cupboard is bare on this one. I'd read about these, but they were released while I was in Germany and were no longer available by the time I returned to the US. I've never seen one show up for sale either, so I still don't have one. I was eventually able to acquire an AVPC though, as they show up for sale once in a while (I had the same problem there, as they went on sale and then were no longer available by the time I initially went looking for one). Well it is a moot point today as there are other RGB options, but I do have the modified console as well as this card, console has the 9928, I believe and I can plug one wire into a video jack on a composite screen and get a gray screen title screen. I may use something to convert the signal to Scart or vga sometime, but I just got in Tang 20k's today and am working on HDMI for the Geneve's. Quote Link to comment Share on other sites More sharing options...
+Ksarul Posted November 27, 2023 Share Posted November 27, 2023 5 minutes ago, RickyDean said: Well it is a moot point today as there are other RGB options, but I do have the modified console as well as this card, console has the 9928, I believe and I can plug one wire into a video jack on a composite screen and get a gray screen title screen. I may use something to convert the signal to Scart or vga sometime, but I just got in Tang 20k's today and am working on HDMI for the Geneve's. Yes, this mod changed the VDP to a 9928. There are several 9928 conversion projects that showed up in various newsletters, and the output from any of them would work with this RGB Interface if routed to the right pins on a DIN6 console connector. 2 Quote Link to comment Share on other sites More sharing options...
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