[Coco] Coco in France

[Gene Heskett]

On Monday 11 February 2019 07:05:55 Carlos Camacho wrote:

> Well, it looks like his power transformer only steps the voltage down
> to 110V but doesn't alter the frequency. So that remains at 50hz.
>
> Refresh my memory... the CoCo needs 60hz in order to generate it's
> NTSC RF video correct? And as I tap into the video signal just before
> it goes to the RF modulator for composite out, that would explain why
> no video there too.
>
No, the REAL reason is that the coco is crashing from low power supply 
voltage, 100 times a second at 50 hertz.  Due to the loss of microfarads 
in the filter capacitor the output voltage is dropping below around 4.6 
volts for a few microseconds everytime the AC voltage reverses, 100x a 
second at 50 hertz.

> He says a transformer that converts to 60hz is expensive so is
> wondering about replacing the internal transformer. Frankly, for me,
> I'd prefer spending the money on a good external transformer and not
> risk my retro gear.

'twouldn't help unless your raised the voltage to around 135 or 140, and 
that would fry that 60 hz transformer in minutes. The transformer will 
probably survive, the REAL problem is the dried out filter capacitor, 
either loss of microfarads, or just as likely, high ESR, which is the 
acronym for Equivalent Series Resistance. Thats generally considered to 
be well done toast if it measures over 2 ohms. A very high likelyhood in 
a part potentially 35 years old. I've seen 5 year old stuff show at 100+ 
ohms. Junk when it was made. Its very difficult to make a gas tight 
metal to metal connection when one of the metals, aluminum, is the most 
reactive metal we have. On exposure to the oxygen in the air, it can 
form an oxide film, also the best insulator we have, with a breakdown 
voltage of about 50 volts, in .0001 seconds. To get any connection at 
all, this oxide film has to be punctured and a microweld has to be 
established to re-establish a connection between the lead or lug and the 
actual highly etched alu foil that may be only .0001" thick inside that 
alu can, and that is the actual capacitor.

> Interesting that he is using same transformer with C64 and other retro
> machines without issues.

They may have filters in slightly better condition. It could easily have 
been the reverse.

Just think, we could still be using Leyden Jars for that but it would 
take several thousand such jars to duplicate what's inside that can.

> Anyhow, I just need confirmation on 60hz power requirement.
>
> Carlos


Cheers, Gene Heskett
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