Right sat down and did a bit of research and came up with this...
The original white PC Engine was a NTSC machine it supported NTSC RF, although the expansion bus at the back had Composite, Stereo Audio and RGB and sync signals. You could get Composite with an AV Booster. The machine became very popular if because against the Famicom it looked and sounded amazing and the Sega Megadrive had not yet come out.
It became popular via grey imports in other places including the rest of asia, europe and the States. However as NTSC RF or even composite video doesn't work on PAL TVs it meant that some people couldn't play the machine. Although RGB existed on the machine very few TVs had a SCART socket and the ones that did may not have supported RGB (this was the late 80s after all, a lot of people didn't even have CD players....).
However some engineers in Hong Kong found a way of reducing the video refresh rate to 50Hz and converting the video signal from NTSC to PAL (which technically isn't all that difficult to do...) and lo the PAL PC Engine was born. It was a third party adjustment and it was soon copied by people who could just barely hold a soldering iron in the UK (cough colin moron diamond cough...).
NEC saw how popular the machine was and decided to launch the machine in the states and would see how the machine would do before commiting to a european launch. The US machine was a lot larger, the official reason given was that it required more RF shielding then the PC Engine to pass FCC tests. However the unofficial reason was that americans would think that anything that looked smaller then the NES would probably be worse and would struggle to do 64x48 pixels in 4 colours and go beep at the same time. NEC struggled to match SEGA and Nintendo in advertising and the machine struggled to sell in any great numbers.
Back in Asia, NEC decided to try and sell the PC Engine in Asia and unofficially made a small number of PAL Core Grafx units and sold them via a distributor, they didn't sell very well and NEC decided not to enter certain Asian markets.
Back in Europe, NEC saw how the PC Engine in France was selling well via a large games distributor who sold converted PC Engine units. Still Grey imports but NEC decided not to do anything except refuse to repair the machines, in the UK the same thing happened when a few distributors sold the machines via mainstream shops, most notablely Hamleys. NEC then decided to convert NTSC units into PAL ones to see if they could shift some units.
The major differences between the PAL and NTSC ones is the fact that the PAL ones have an Composite AV socket on the machine rather then an RF connector (although an PAL RF box came with most machines). No machines were sold as RGB machines although in France some machines were converted to RGB SCART by the distributors.
NEC did dither about which regions they would sell them in, mainly due to the success of the Sega Master System, Nintendo NES and even Sega Megadrive and the slow sales in the states. Several distributors came up including some investors in the UK that claimed they would sell the TG16 in the UK (which they er didn't). In the end they decided not to sell the machine officially anywhere in Europe. However they did let distributors sell the machines and NEC would at least honour the warrenties. They turned up in Spain, France, the UK, Germany, Italy and Austria and they even were sold in Argentina, South Africa, New Zealand and Australia.
Most of them were unsold and a distributor did sell most of the European stock to various distributors includig Lik Sang and Telegames.
