Can you upload the other pcb photos?
Here is R7 at 2.7K(red violet red) and 270(red violet brown): https://tsk-tsk.net/net/temp/sfx_r7.zip

- power on
- synth mode
- press a note key (resets parameters)
- F12C
- play keys EDCBA
- F30C
- play keys EDCBA

Which one sounds more like the real one?
I don't mean the pitch or the decay rate, but the buzz in the background, especially on F30C with R7=2.7K.

Youtube video of Coleco Galaxian, fast foward to 2:30

Sound is too high pitch for me to determine by ear if it's a saw wave. And I don't really care what the exact waveform is, just that it's not simple enough to simulate accurately without a netlist in MAME.