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

[Gene Heskett]

On Saturday 04 October 2014 13:34:39 Luis Antoniosi (CoCoDemus) did opine
And Gene did reply:
> 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/Col
> or%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.
> 
I might point out that if its a PAL machine, the modulator probably is not 
outputting on an American channel known as 3 or 4.  Frequency assignments 
for TV usage varied from country to country, even for those using NTSC and 
IIRC there were several variations among the countries using PAL too.

So spin the dial on the tv, you may find its signal on some other channel, 
but on an NTSC TV, it probably will be all out of synch & un-usable.  And 
its possible it is not findable on an American TV.  

And, while I thought SK was using NTSC, and pretty close to our channel vs 
number assignments, I've not much of a clue what is the defacto standard 
where you are Luis. IIRC you are in South America someplace?


Cheers, Gene Heskett
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