I followed your guide step by step and got beautiful RGB from my NTSC TI-99/4A!!!   I replaced the TMS9918A chip with a TMS9928A from eBay (A socketed IC--what a breeze!). I soldered on the TMS-RGB, and added the 560 ohm resistors on the lines where indicated. 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, with the