Atari 2600, video mod
Frustrated by the results of my slightly unsuccesful Atari 2600 video mod, I ended up buying a RetroKidz composite / S-video mod from (the nowadays ceased) 8-bit Domain webshop shortly after. The specs available there stated that this mod had been tested to work on both PAL and NTSC systems, so it seemed like a hassle-free solution.. Not that it proved out one, really. If you have a PAL system and this mod installed, you should definitely read on!
Ok so after receiving the mod, it turned out to be a slightly modified copy of Thomas Clancy’s CD4050 video mod. I haven’t bothered completely reverse engineering the circuit, but at a glance this RetroKidz version seems to have only an alternate input/output pin order on the 4050 compared to the schematic on the link above. The entire circuit has been implemented with SMD components.
Much to my annoyance, despite the picture quality was ok the colors were mixed up. I don’t know how many times I checked the connections but nonetheless, I was unable to find anything wrong. As I had strong belief, that someone manufacturing mods such as this would know what they’re selling (“tested to work on PAL/NTSC systems”) I didn’t bother looking deeper into why the colors might be b0rked. I just assumed I have a damaged TIA and boxed up the Atari to the basement. Spare parts should come my way sooner or later..
Some sure did, but so did a discussion about Atari 2600 video mods with Visy / Wamma^Trilobit too. Having done quite a bit of coding on the 2600, Visy knew to point out that there are actually separate NTSC and PAL versions of TIA and (wonder if you guessed/knew this already?)..: They don’t share the same pinout!
I never recall reading about this fact anywhere but believe me when I say, I’ve definitely done my reading about the various Atari 2600 video mods. Chip recognition is easy: PAL TIA is labeled CO11903 whereas NTSC is CO104444. Needless to say, I was pretty fucking disappointed at 8-Bit Domain after hearing about this. Either the person who made this PCB is entirely color blind or the board was never tested on a real PAL system. Yeah, fuck you too and thanks for wasting tons of my time for not doing YOUR homework before knocking up a PCB.
Sure enough, there’s a PAL/NTSC jumper on the PCB. However, this simply routes pin 12 of a PAL TIA to the main board (sync osc circuit) or bridges pins 12 and 13 together for a NTSC TIA (AUD0 + AUD1 summed). Despite this, LUM signals are hardwired for NTSC TIA! So, in order to make this mod PAL for real, LUM0 and LUM2 need to be rewired.
After having had this repair pending for several years, it’s now time to make it work by modding the mod! :)
Not much to it, pins 5 and 9 of the 4050 get lifted from the board and wired to the proper pins on the socket instead. Come to think of it, digging up the box of Atari stuff from the basement was far more bigger a task!
As for audio connections, since PAL TIA has only one audio out (pin 13), the L/R wires on the audio output can be shorted together (mod kit comes with a 3.5mm stereo jack) . I just added a blob of solder on the connector header.
While at it, I also ended up replacing the TIA socket. After having seen a lot of TIA / video mod reseating over the years, it’s single-wipe contact pins were starting to cause random problems on the video. Nothing a new machine tooled socket wouldn’t cure :)
If you’re totally unfamiliar with Atari 2600 demoscene stuff go check out this list of releases. I’ll leave you with a video capture of the amazing ‘(c0re)’ by PWP & Trilobit. How nasty can a Atari 2600 speech synth sound..? ;)