UPDATE 2021-01-02 – I’ve created a repo with the datasheet for the main encoder (and other MStar chips) at https://blog.obsoletemadness.com/2021/01/02/mstar-datasheets/
I recently purchased a couple of cheap SCART to HDMI adapters from AliExpress. The first one I ordered claimed it could do both 50 and 60hz output. Unfortunately, it didn’t have a button to do the toggle and after a prolonged fight with the vendor I got a refund.
So I tried a different model. This one clearly had a PAL/NTSC button on it. (As an aside, while today the price difference between the two models is about $1, when I originally ordered these, the second one was almost $20 dearer).
Sadly, while this one could output 720/1080p@50hz it would corrupt the display after 30 seconds. Rather than be stuck with two adapters that didn’t work the way I needed, I decided to see if I could add a PAL/NTSC button to the one that did work!
Looking at the two devices it was clear that one was simply a cost reduced version of the other (at the time I bought them, there was nearly a $20 difference, it looks like they’ve come down a bit since).
So, I traced where SW2 on my broken board. SW2 goes directly to whatever pin this is on this unknown chip.
The way I did this was to wire one end of a switch to the unpopulated R103 pad closest to U14. I then wired the other end of the switch to ground via a 470 ohm resistor.
Finally I drilled a 6.5mm hole in the front SCART connector face of the case and pushed the switch through.
Behold! 50hz output!
Is this worth it? Only if you already have the adapter without the PAL/NTSC toggle. If you’re buying one the price difference between the two devices is only $1 now – and the one with the toggle has HDMI input, and Coax digital out.
A quick review
These boards do what they promise, they convert SCART (including RGB) to HDMI at various output resolutions. The video quality on them is quite good – and they’ve worked with everything I’ve tried (C64, Amiga RGB, Sega Megadrive, SNES). The usual caveats apply for progressive 240p-ish sources. There is a de-interlacing filter on them that bobs the image slightly.
I need to find out what the two unknown chips are on the board (U11 and U14). U14 is clearly a micro of some description, handling the button presses, etc. U11 looks like an LCD TV SoC (which makes sense). But what one? The headers for what I think is the ISP are quite clear – so perhaps there’s an opportunity to (say) disable the de-interlacing.