[Coco] video composite on korean coco 26-3134A

[Luis Antoniosi (CoCoDemus)]

This is a pal machine:

https://lh5.googleusercontent.com/-R2PDAlwUyC8/Ukef7tm_2iI/AAAAAAAAHQg/S6ZXnbdbq2I/s912/WP_20130928_020.jpg

Cocos2 are the second easy machine to repais that I found, being the coco1
the first.

service manual:
http://www.colorcomputerarchive.com/coco/Documents/Manuals/Hardware/Color%20Computer%202%20Service%20Manual%20%28Tandy%29.pdf

steps:

1) check the +5V, either on Chip vcc terminal or the test points. If the
+5V is not ok, then check the capacitors and power supply transistors (AC).
If they are ok, check the SALT chip. It serves as voltage regulator and
also other things.

2) being the voltage ok, check for the 6847 video output. it generates
composite monochrome video direct from pin Y (pin 28). The mc6847 is
already wired for text video output upon start. If there is a clock and
power supply it will generate video. There is no way to disable it.

3) if 6847 generates video check the 1372 connections. It should receive
6847 Y, 0B, 0A and clock.







Luis Felipe Antoniosi



On Sat, Oct 4, 2014 at 1:01 PM, Zippster <zippster278 at gmail.com> wrote:

> Ah, ok.  He could look for that chip then to verify it’s PAL.
>
> -Ed
>
>
> On Oct 4, 2014, at 11:24 AM, Luis Antoniosi (CoCoDemus) <
> retrocanada76 at gmail.com> wrote:
>
> > the PAL machines have an extra chip on it connected to the 6847 as this
> one
> > cannot generate 50 Hz PAL video.
> >
> > Luis Felipe Antoniosi
> >
> >
> >
> > On Sat, Oct 4, 2014 at 9:50 AM, Zippster <zippster278 at gmail.com> wrote:
> >
> >> The crystal on the motherboard should tell you wether it’s PAL or NTSC.
> >> It’s divided by 4 for the subcarrier frequency.
> >>
> >> 14.31818mhz = NTSC, PAL should be 17.73448mhz
> >>
> >> - Ed
> >>
> >>
> >>
> >> On Oct 4, 2014, at 8:05 AM, Bruce W. Calkins <brucewcalkins at charter.net
> >
> >> wrote:
> >>
> >>> If it is a 50 Hz power supply the TV output is probably useing the
> >> European PAL standard.
> >>>
> >>> Bruce W.
> >>>
> >>> ==================
> >>>
> >>>
> >>>
> >>> ----- Original Message -----
> >>> From: "didier derny"
> >>>
> >>> I tried, I was not expecting a correct image, but at least something
> >> like a
> >>> synchro
> >>> But nothing, just snow...
> >>>
> >>> The tv see a "VCR" but no signal
> >>>
> >>> Any idea if the modulator or the coco uses the 60hz ?
> >>> The power supply is 110v but 50Hz
> >>>
> >>> That's why I have a serious doubt about this machine...
> >>>
> >>> --
> >>> didier
> >>>
> >>> -----Message d'origine-----
> >>> De : Coco [mailto:coco-bounces at maltedmedia.com] De la part de Zippster
> >>> Envoyé : samedi 4 octobre 2014 00:17
> >>> À : CoCoList for Color Computer Enthusiasts
> >>> Objet : Re: [Coco] video composite on korean coco 26-3134A
> >>>
> >>> You could rig up a quick and dirty piece of coax cable from the RF port
> >> to
> >>> the antenna in jack on a tv and tune it to channel 3 or 4 (whatever the
> >>> switch is on).  The picture may not even be that bad.
> >>>
> >>> Or the relay.
> >>>
> >>>
> >>> -Ed
> >>>
> >>>
> >>> ---
> >>> This email is free from viruses and malware because avast! Antivirus
> >> protection is active.
> >>> http://www.avast.com
> >>>
> >>>
> >>> --
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> >>> Coco at maltedmedia.com
> >>> https://pairlist5.pair.net/mailman/listinfo/coco
> >>
> >>
> >> --
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> >>
> >
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