[Coco] CoCo in France

[Gene Heskett]

On Sunday 10 February 2019 10:59:23 Francis Swygert wrote:

> From: Carlos Camacho <idevgames at gmail.com>
>
> Let me recap my previous post...
> 1) NTSC Coco (mine)
> 2) NTSC TV (his)
> 3) He's using a step down transformer
> 4) He says other video game consoles (NTSC) are working with his
> transformer and his NTSC TV
>
> I asked him to try the RF output to the NTSC. He says that too has no
> video.  I asked him to turn on the machine and enter the SOUND 100,10
> command. He reported no sound on the audio out. I need to have him try
> the sound test again over RF.
>
> I was also thinking a difference in the 50hz vs 60hz. Could it be the
> 'other retro' systems he mentions (that he bought from the US) have
> less of an issue producing a video if his transformer is handling the
> hz as is expected. ie a 30+ year old system vs a 10+ year old system.
>
> ================================
> Since the CoCo converts from AC to DC internally the 50hz vs. 60hz
> shouldn't matter. AFAIK there is no use of direct AC for anything.
> Since this is a CoCo1 it is possible that one or more chips got
> dislodged during shipment. You might want to have him crack the case
> open and push down on all socketed chips. Sounds like maybe a RAM, the
> SAM, or 6809 might be up in the socket enough to not get a good
> connection.

I'll make a SWAG here after putting on my CET hat, and say the big 
electrolytic capacitor on the mainboard, not too far from the bigger 
transistor on a heat sink of sorts was getting pretty well dried out, 
and while it could hold a usable voltage during the low voltage portion 
in a 60 hz wall supply, but is falling short on the longer low voltage 
period of a 50 cycle supply. We tend to forget that these things are 30+ 
years old, and the average life of such is not measured in multiple 
decades.

Not to mention that the power transformer in the coco was a 60 hz rated 
one, and is going to run 15 or so degrees F warmer on 50 hz, due to the 
longer time the primary current has to build up, approaching the 
saturation point of its iron core.

So at a minimum, that cap might need replaced.

If the iron does saturate magnetically the current flow in the primary 
will rise to resistive limits and will likely toast the transformer at 
some point, compared to the 100+ years it will run on 60 hz. But IIRC 
there's a fuse on that little pcb which might interrupt that.  If it 
clears, the coco will be completely dead. I've only seen one of those 
fuses fail, so its not a common occurrence on 60 hz power.

That capacitor, IIRC is a 4700 uf, and on 50 hz power, a 6800 uf would be 
a better replacement.

Good luck Carlos

Cheers, Gene Heskett
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