Goldstar FC-200 VDP Oscillator replacement

The normal clock frequency for the VDP should be 10.738636 MHz (3 * 315 / 88 MHz), but on PAL machines the clock frequency is often tweaked to get a more in-spec PAL signal frequency with a 15625 Hz horizontal scanning rate. I presume to improve compatibility with 80’s era TVs. The crystal frequency used is therefore 684 * 15625 Hz = 10.6875 MHz (where 684 is the nr of master clock cycles per line).

At the normal clock frequency the VDP outputs lines at 15700 Hz. Note that this is also slightly out of spec for NTSC (expected 15734 Hz) so Texas Instruments took a middle ground value that was “good enough” for intents and purposes with both PAL and NTSC outputs. p.s. Note that progressive scan itself (“240p”) is also out-of spec, liberties were commonly taken with video signals in 80s game consoles.

Since on this machine the CPU clock frequency is derived from the VDP clock, it also means the CPU runs slightly slower at 3.56 MHz rather than 3.58 MHz.

Btw nice hand-drawn schematics in that service manual!

i also suspect that even the psg sound is affected in tone frequency by the slower clock rate

But the crystal in the OP's first pic is not the system clock, it's the video modulator clock.
In the WIKI there's a couple of pictures, I can only read the value of the French version (the usual PAL 4.43 MHZ), so probably the PAL version is the same value.

Whilst that is not wrong (it is true for every MSX), it is not what Pentarou was saying. The oscillator that was replaced is not the actual source for the VDP master clock. It is used solely on the video board (which just takes the video signals from the VDP and creates the RF/RGB/composite depending on the model), I am not sure what for exactly it is there. The main oscillator that drives the VDP is just above the VDP and is marked as 10.6875MHz. So that the 10.7MHz oscillator is working on the X-TAL location on the video board seems like pure luck.