It might have been missed since it's buried in another thread (http://atariage.com/...c-needed/page-2), but just wanted to share this awesome MOD and document it in its own thread.
Parts used for this mod: AY-3-8900-1 NTSC STIC, 3.5795MHz crystal
A bit of background - The PAL territory Intellivisions run many games at different speeds to the USA version of the console. The PAL CPU runs faster, but the video refresh is slower. Since the games are synched to the video refresh, the gameplay is slower. The pitch and speed of the sound is different too thanks to the different speed the CPU runs at.
Most notable is D2K - the game and music runs around 12% slower, and the sound pitch is higher. Dreadnought Factor won't run at all on a PAL system.
I picked up a model 3668 PAL Australian Intellivision that turned out to have a bad AY-3-8900 CCIR PAL STIC. I had no spares of this chip, but had an AY-3-8900-1 NTSC version of the chip lying around. Since the two are pin compatible, I speculated if it was possible to swap the NTSC chip in and mod the system to run at USA clock rates, and to produce a PAL60 RF signal - 60Hz refresh with PAL encoded colours.
Earlier 3668 model Intys seem to have a daughter board that produces the colour information, this Intellivision motherboard revision does not have this daughter board and instead has an onboard colour chip. It shouldn't matter which version your system is.
I swapped just the STIC out and tried the system - it worked, but the video was out of synch.
The PAL Intellivision has two crystals onboard - one at 4.4MHz for the PAL colour generation, and a 4.00MHz system clock (nearest the CPU). I swapped the 4.00MHz crystal for a 3.5795MHz crystal and tried it again - it worked!
The system runs at the correct clock rates, with correct USA game speeds and sound pitch, on a PAL 60 TV. The picture quality is excellent. As an added benefit the picture fills up more of the screen.
I am astounded at how simple the mod was, I was fully expecting to have to make further mods to the RF video circuit, but the RF circuit is unchanged. Since the mod is so simple it should be compatible with other mods, eg composite mod.
A big THANK YOU to intvnut for his technical assistance with this mod!
It should be noted that I am using the modified console with a later Sony CRT that supports 60Hz refresh rate, obviously earlier 50Hz PAL CRT TVs won't be able to synch with the modified video signal.
Edited by HunterZero, Tue Oct 11, 2016 7:18 PM.