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RGB Mod Explanation

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On 3/27/2021 at 10:28 PM, webdeck said:

Success!  I followed the instructions in Post 28, namely:

  1. Disassembled the console
  2. Removed the 9918A with a chip puller
  3. Soldered a ribbon cable to the TMS-RGB
  4. Soldered the TMS-RGB (ordered from Mobius Strip Technologies) under the VDP socket on the back side of the board
  5. Soldered a wire to the sound output
  6. Desoldered the video connector and removed it from the board
  7. Desoldered the one resistor that was where the bottom 560 ohm resistor goes
  8. Added and soldered the three 560 ohm resistors
  9. Soldered the ribbon cable and audio cable to a mini-DIN 8 jack following the XRGB wiring diagram (using this helper board)
  10. Bent back the shield near the mini-DIN jack to make enough space for the new connector + wires
  11. Attached the mini-DIN jack (upside down) to the board with solder and hot glue, using a nut as a spacer (otherwise it is too low for the opening)
  12. Double-checked continuity between the pins of the mini-DIN jack and the TMS-RGB and checked for shorts
  13. Cleaned off all the old thermal paste from the shield
  14. Inserted a TMS9928AN (purchased a used one pulled from a working system on eBay) into the VDP socket
  15. Applied new thermal paste to the VDP
  16. Covered soldered wires with electrical tape
  17. Put electrical tape around ribbon cable where it comes near the shield to go around the board
  18. Put everything back together
  19. Connected the mini-DIN jack to my OSSC's SCART connector via the recommended cable
  20. Set the OSSC for AV1 (SCART) RGBs

I powered it up and got the most beautiful crisp title screen.  Audio works fine with the SN94624 sound chip.  My TI has never looked this good!




I made the same mod with the TMS-RGB board and the Mini Din 8pin. 

I have a nice and crisp picture but sound is very low and I can barely hear it.

I connected both L/R audio cables to the pin 5 of the DIN connector. I have a PAL machine by the way.

I am missing something to get louder audio output?



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  • 1 year later...
On 3/7/2021 at 11:00 PM, mdfk said:

Where I marked here, there was a resistor (22 ohm?) already populated on the board, with its left leg going into the left throughhole (orientation matching the image). I removed it and replaced it with 560 ohms

I removed the "22 ohm" part and checked it:  On my NTSC TI system it is a 25 microhenry inductor.  So, I added the inductor back to the circuit, just assuming it is there to help with noise, and also added the 560 ohm resistors.

Thank you to everyone on this thread for providing instructions and notes!  RGB output is looking amazing on my NTSC TI-99/4A!

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