[Coco] need help repairing a coco 2

[didier derny]

I have a coco 2 with no video on tv output.

 

I built the composite interface on a breadboard

Obviously I'm getting an image. 

 

But the machine is not correctly starting

 

When I start or reset the machine I get

The following patterns:

 

1/ Orange screen

 

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

 

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

So my "theory" is that the 6809 starts

 

The coco 2 is a 16k Korean one with 2 small sockets beside the ram chips

 

Any idea ? it's the first time I repair a coco

 

Thanks

 

--

Didier