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PAL Coco Differences

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Home / Articles - PAL Coco Differences


A guide to the various PAL Coco systems

Some other things just came to my mind (which is a little bit rusty after all these years):

I own PAL CoCos (and MC-10s) from different areas and they are all slightly different.

AFAIR, there's one group which has been sold in Germany, Belgium & the Netherlands (CoCo 1 to 2B). These are following the PAL-G standard and have a modulated RF video out on UHF (0.3-3.0 GHz) channel 36 (this channel was originally kind of reserved for this purpose: computers, video recorders, etc. In times where you only had 3 terestrical analog TV programs and not yet SCART and/or composite video inputs in your TV sets). A channel switch was not present (the corresponding hole in the CoCo's case was covered by a plate reading "Channel 36").

Some key dates for PAL-G:

  • Vertical scan lines: 625
  • Vertical frequency: 50 Hz
  • Horizontal frequency: 15.625 kHz
  • Video band-width: 5.0 MHz
  • Audio carrier: 5.5 MHz
  • Color subcarrier frequency: 4.43361875 MHz
  • Channel spacing: 8 MHz
  • Vision modulation type: AM
  • Vision modulation polarity: negative
  • Sound modulation: FM
  • Vestigial side-band: 0.75 MHz
  • Field period: 1/50 s = 20 ms

There's another type sold in United Kingdom (Great Britain [England, Scotland, Wales] and Northern Ireland), I assume this one follows PAL-I standard (difference to PAL G: Video band-width is 5.5 Mhz [instead of 5.0 MHz], Vestigial side-band is 1.25 MHz [instead of 0.75 MHz] and the audio carrier is at 6.0 MHz [instead of 5.5 Mhz]). The latter has the effect, that on a PAL G TV you can either have the sound correctly tuned or the image. It was rather using VHF (0.03-0.3 GHz) [instead of UHF], so it had the "Channel 3(?) or 4(?)" select switch.

From Australia, I got at least some PAL CoCo3 (the PAL CoCo3 had never been sold in Europe, because Tandy/RadioShack closed its stores in the time the CoCo3 came out. The CoCo2B [lower-case, 6847-T1 VDG] was never officially available in Germany, but I got one with a very low serial number which was a demonstrator from our local store). Australia has PAL B/G, and AFAIR the machines have the VHF "channel 2(?) & 3(?)" switches, so I assume CoCo3s are PAL-B machines. However, you would rather use the composite video out or the RGB out with a CoCo 3 and not the RF modulator. Composite video out is generated from the RGB out with a piggy-backed satellite board, the GIME's NTSC composite out is not connected on PAL boards. The PAL CoCo3 has a modified PAL ROM too (initializing the GIME to 50Hz video timing).

The strangest group of machines (CoCo1 to CoCo2B) come from France. These have a French AZERTY keyboard layout [instead of QWERTY in both the US and the rest of Europe, at least in Germany we would have prefered a QWERTZ layout, but noone cared :-)]. The modulator has been completely replaced by a VDG to RGB circuit, which is compatible with the French SECAM-L TVs. For the sake of completeness, a SECAM-L RF modulator would have to comply with the following (I think they were sold as an external device):

  • Vertical scan lines: 625
  • Vertical frequency: 50 Hz
  • Horizontal frequency: 15.625 kHz
  • Video band-width: 6.0 MHz
  • Audio carrier: 6.5 MHz
  • Color subcarrier frequency: 4.406250 MHz/ 4.250 MHz
  • Channel spacing: 8 MHz
  • Vision modulation type: AM
  • Vision modulation polarity: positive
  • Sound modulation: AM
  • Vestigial side-band: 1.25 MHz
  • Field period: 1/50 s = 20 ms

The French CoCo PCBs have an additional +12V voltage generator on board, which is output along with R, G, B, H+V (which is AFAIR actually a composite sync signal) on a small Mini-DIN connector. Then you need a special Mini-DIN to Péritel (=Euro-SCART) cable, which contains voltage devider to create switch voltages which set the video sink (the TV) to RGB mode (rest-of-Europe SCART often runs on composite video mode only).

Hope that is kind of interesting (depite it doesn't solve your problem yet).

Best regards, Torsten