Making a SCART cable for 6128

[wcameron2005]

I've made a cable based on the "Amstrad CPC to SCART" diagram from the below site:

https://www.cpcwiki.eu/index.php/TV_SCART_cable

The cable works fine on my Philips CM8832 monitor (albeit a little noisy), but not on my Akura AHLTV15 (cheap 15" LCD tv): the TV displays a "SCART (AUTO)" message, but nothing but a black screen. I'm using a12v power supply to provide power for pins 8 and (via a 470 ohm resistor) 16. I've tried various things, but the screen flatly refuses to display a picture.

Any help greatly appreciated.