[Coco] PAL Cocos

[Jayeson Lee-Steere]

Torsten,

That is kind of interesting indeed, as in kind of very interesting. I have
an Australian Coco 2 and a 3 here. I knew quite a bit of what you
discussed, to some degree, but this info is hard to find, so thank you for
the full rundown. I was reading up on the Coco 3 NTSC vs PAL differences
last night when I should have been sleeping. I did notice that GIME pin 56
was not connected on the PAL model and was going to wire in the simple
composite output circuit from the NTSC model. However it occurred to me
today that the crystal is slightly off so NTSC colors still won't work.

It looks to me that you can get the PAL Coco 3 to 60Hz by forcing the RGB
monitor detect pin low? Actually, I just found you can clear the GIME 50Hz
bit in software. BASIC likes to set it back though however since BASIC is
running from RAM, changing BASIC's variable does the trick. My Coco 3 is
running PAL-60 right now. Much less flicker, much wider black lines between
the scan lines.

Jayeson


On Thu, Feb 28, 2013 at 11:29 PM, Torsten Dittel <OS-9 at trs-80.cc> wrote:

> Jayeson,
>
> I should have several Service Manuals for differnt CoCo1 to CoCo3 PAL
> models
> (access might be not that easy currently because it's all stored in
> boxes). If
> noone else finds these and/or has it already scanned, I might give a try
> to dig
> them out.
>
> 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
>
>
>
>
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