[Coco] CoCo RGB video timing and levels

[KnudsenMJ at aol.com]

In a message dated 8/24/04 12:20:09 PM Eastern Daylight Time, 
neilsmorr at hotpop.com writes:

> Probes you can get off eBay or from a electronics jobber. They may cost more
>  than the scope (go figure).

Probes tend to break and wear out, due to frequent handling.  Make sure any 
used ones you buy (or that are included with a used scope) are known good 
before you buy.

>  Same as a computer - European DIN 6 amp. Really old ones may use an odd 
ball
>  cord.

*Really* old scopes will have the cord permanently attached to the rear.  But 
you don't want a really old scope unless it's a Tektronix 500 series, which 
will keep your house warm in the winter and prevent your workbench from blowing 
away in hurricanes :-)
 
>  Go to the library and look for, "How to use your Oscilloscope" or similar.
>  An ARRL handbook or a generic test equipment book may help also.

ARRL (Ham Radio) books are good.  One good thing is that on a scope with a 
lot of controls, there are only a few that you need to know how to operate at 
first.  The trick is to set the others so they stay out of your way.

Make sure the scope has enough bandwidth -- at least 10 or 25 MHz.  50 or 
even 100 MHz is best.  There are plenty of old TV-service scopes that are only 1 
MHz or so.  They aren't much good for digital work, even on our brontosaurus 
Cocos.

Vertical sensitivity -- you don't need much, maybe 0.1 V/cm.

You can get started with only one vertical channel and no external sync 
input, but very soon in digital work you'll want at least two channels and external 
sync.

Recent TV-service scopes are probably high enough BW for working on a Coco, 
and have built-in preset sweep rates for TVs.  Since the Coco's clocks are all 
based around color TV frequencies, that may be a plus.  I've gotten along fine 
without the TV sweep rates in my scopes, but that's a thought.  --Mike K.