[Coco] need help repairing a coco 2

Didier Derny didier at aida.org
Thu Oct 16 03:02:54 EDT 2014


the 6847 can produce the "beginning" of an image without being programmed ?

the 6809 can be only partly blown ?

thanks

--
didier


On 16/10/2014 00:25, Retro Canada wrote:
> its pretty easy through a mialigned cartridge to blow the 6809. you coul blow it entirely or some pins. this is the first thing to replace. the second is the ram chips. the you go for sam and pias.
>
> the 6847 is working fine
>
> On Oct 15, 2014, at 6:14 PM, "didier derny" <didier at aida.org> wrote:
>
> I have a coco 2 with no video on tv output.
>
>
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> I built the composite interface on a breadboard
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> Obviously I'm getting an image.
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>
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> But the machine is not correctly starting
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>
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> When I start or reset the machine I get
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> The following patterns:
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> 1/ Orange screen
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>
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> 2/ mix of green/orange lines not correctly synchronized
> http://netfilters.eu/p2.JPG
>
>
>
> 3/ black screen with random green square containing the letter 'P'
> http://netfilters.eu/p3.JPG
>
>
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> 4/ mixed pattern, orange bands with green square containing the letter 'P'
> http://netfilters.eu/p1.JPG
>
>
>
> I removed all the component on socket and clean the pins.
>
>
>
> If I remove   ram or sams or  eprom I don't get any image
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> So my "theory" is that the 6809 starts
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>
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> The coco 2 is a 16k Korean one with 2 small sockets beside the ram chips
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>
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> Any idea ? it's the first time I repair a coco
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>
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> Thanks
>
>
>
> --
>
> Didier
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>



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