I used the schematic from Atariage FAQ (the CD4050 mod) on a PAL 2600jr and it works great! You only have to find where to pick the signals since the TIA pinout is different between PAL and NTSC. The junior (and 6 switch) already have the luma and sync signals buffered by a CD4050 chip, so the mod is a little simpler than on a 4-switch.
Here is a schematic of the circuit (exactly the same one on AA faq but without the CD4050, cause I used the one already installed on the console)
signals on the board:
Sync: R51, upper side (CD4050 pin 12)
Lum0: R52, upper side (CD4050 pin 2)
Lum1: R49, upper side (CD4050 pin 10)
Lum2: R53, upper side (CD4050 pin 15)
Color: R29, bottom side (TIA pin 9)
Audio: W2, upper side (TIA pin 13)
Power (+5v) and ground can be tapped into many different places on the board and are not indicated in the pic.
For example, power can be found at any point continuous with the right pin of the voltage regulator (with printed side facing you and pins pointing downwards), while ground at any point continuous with the center pin of the regulator or with the metal shield.
The pic refers to a PAL-B, rev. B board. I've seen some images of PAL-I (for UK market) junior boards and they have a slighty different layout, so you may need to change something. (use the schematics on AA as reference)
I removed resistors R49,R51,R52,R53 and R55 and cut the center pin of transistor Q3 and Q4. This should avoid interferences with the mod and reduce power load of the console but it's not necessary and, since I'm quite inexperienced in electronics, I'm not even sure this is the correct way to do it. (Suggestion from electronics experts are welcome!)
I removed the rf connector and used the hole left in the case for the new scart cable that I soldered directly on the mod board. I also modified the channel select switch to select between composite or s-video (you need to cut some traces on the board and solder a couple of jumper to isolate the switch from the rf circuit). In this way I avoided to drill or modify the case in any way. Next time I plan to make the cable removable using a 6-pin mini din connector (like those used for PS-2 computer mouse and keyboard) with luma/composite, chroma, audio and ground signals.
The hole of the rf connector is the right size for mini-din, so this shouldn't require any case mod too.
Edited by alex_79, Thu Jul 3, 2008 1:53 PM.