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JJB

TI99/4a and TMS-RGB

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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

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@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 😛

 

image.thumb.png.4b01bfce8e53a3809e206e39d66de4e1.png
 

 

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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 by RickyDean
spelling - thick fingers

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this one? http://www.mainbyte.com/ti99/hardware/peb/avpc.html 

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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 by RickyDean
added content

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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 by JJB
Removed AC-coupling; sync noise solution
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