Bas From BetaGamma here.

I’m going to be honest with you its a pretty bad install, I can see lifted tracks, shorts and you are hooking up to wrong pins left right and centre.

These mods do require a degree of precision as there are some fine micro pitched legs on the main chip.

There is an official install document I produced which…Read more

The TMS video out signals rely on external pullups, 270R if memory serves, but pls check the schematics.

The original board probably had the required pull up resistors on it.

Answers to your questions

1. Yes this is the way, dont double buffer or you will delay csync timing

2. Yes remove it

3. See VGPs response

ST and STe scart cables are notorious for sync issues where scart cables are concerned…

This is because they don’t natively have 5 or 12 Volts on the monitor connector which is usually used by other systems to derive the Fast blank switching voltage on scart Pin 16 which TV’s need to be informed to use RGB signalling instead of…Read more

My advice is use the buffered sync from the scic board

Cut the tracks for RGB at the video out port then stick the rgb board in place.

Run the RGB signals from the mainboard as identified in the docs but use the scic out for csync

5v shorted to red indicates the red output was shorted or cabled up incorrectly causing the chip to fail.

The soldering in general concerns me, there appears to be pcb damage to the one board near the chip leg pads…

I assume you have insulated the…Read more

I would try reflowing the 3 signal inputs using some liquid flux.

I also notice that you are using a megadrive cable. These cables have inline components and its recomended you remove the three resistors on the tmsrgb board and jumper them instead. If your cable also has a csync inline resistor you will need to connect to the other…Read more

You can also check the B output of the board with the scope.

But basically you are missing Blue

As replied above, you can ignore R18 being replaced due to the cable you plan to use.

Regarding the RGB lines, it is your call tbh the vias alongside the resistors are indeed tracked to them.
some people shy away from soldering direct to VIA’s as they can be delicate, but if you use thin enough, eg AWG30 kynar you will be…Read more

Before fitting the board to a junior you need clop the pins on 3 capacitors, the 2 in your picture and one further right.
Also ensure you insulate the underside…Read more