Converting a NTSC 1200 to PAL

[Zac67]

Pin 41 of Alice is controlled by R203 - if removed/cut _NTSC/PAL is switchable by the Sony video encoder U12.

The switching signal is output through pin 7 and inverted by Q201. PAL machines have additional components (crystal Y451 et al) to generate the color clock, maybe U12 checks for that signal. All this is not needed if you just use RGB output.

Hmm, with R209 in place (Rev 1B+), the U12 logic doesn't make much sense - it's simply not able to pull down _NTSC... If you just cut the R203 bridge, you should have PAL.

For complete PAL compatibility you need to replace the modulator (else you lack composite) and the crystal (else genlocking might be a problem), too.

[Zac67]

I was just exploring the schematics - just disregard the second paragraph and it makes a lot more sense.  :-D

U12 (Sony chip) sits in the top left hand corner, a bit below that you find Q201 (three legged transistor) and to its left is R203 (black resistor) - looking at BBoAH photos it actually seems to be a real SMD resistor, not just a bridge. Can anyone verify that it shows '000' like my (bad quality) schematics state? Removing this or cutting one of the traces should make it a PAL Alice.

[Zac67]

willow wrote:
... connecting pin 41 of the Alice custom chip to ground causes the A1200 to default to NTSC, while pulling this pin high (disconnecting it from the motherboard and connecting it to +5V through a 4.7k resistor) will make the default power-up state PAL.

No need for pullup though - Agnus/Alice has an internal pullup.

[Zac67]

adolescent wrote:
When you switch by changing Alice (or Agnus, etc.) and don't change the motherboard crystals you end up with NTSC-50Hz (or PAL-60Hz if it's a PAL model).  For example, on my 1% TV I get a signal, but no color if I use a PAL Amiga.

The crystal swap is needed to reach the exact clock you need for genlocking, connecting an A2024 etc. To get proper (enough) composite - whatever that's worth :-P - you need to exchange the modulator and (NTSC -> PAL) add the missing components for the PAL color clock.