[vcf-midatlantic] Vintage computer finds at the Sussex Hamfest

Herb Johnson hjohnson at retrotechnology.info
Mon Jul 18 22:36:19 EDT 2016


Jonathan wrote:

 > Perhaps that's why people aren't interested in 20 MHz "student"
 > or "TV" 'scopes but will spend money on USB connected device
 > that claim 100+ MHz bandwidth...

Jonathan knows about, what I'm about to post....

Note that I cast those 20-40Mhz scopes as alternatives to logic probes; 
a low bar. It defies my old-person 20th century mind, that someone would 
try to debug TTL logic and 4MHz processors with a logic probe and 
interpret a blinking LED. When most any 'scope with triggered sweep will 
provide means to check timing and logic states at 8-bit processor 
speeds. Not to mention, funny logic levels that will confuse gates, and 
indicate fried TTL drivers or possibly shorted lines and connections.

I'd say most 1970's microcomputer failures could be "caught" with this 
class of oscilloscopes, used with some knowledge and experience and a 
TTL data book.

What such scopes won't do, is catch "glitches", odd logic events due to 
faulty timing or noise artifacts treated as logic signals. That's when a 
100Mhz true analog bandwidth starts to become useful. And at that, you 
may need a storage 'scope to catch one-off events.

While I've bought and used simple "TV repairperson scopes"   - I 
actually see better 'scopes than that, go begging. One I picked up 
Sunday, has some kind of digital storage, but otherwise analog. The 
other is a lower-end Tek scope with some digital controls. One acquired 
late last year, was 40Mhz and had some digital display features.

As for USB-based "oscilloscopes", those are analog-digitizing devices 
which use a PC for display and operation. Sample rate does not equal 
bandwidth, an LCD does not equal a CRT. (hooking thumbs in suspenders) 
While I don't know much about 'dem fancy, hew-hess-bee, citi-fied ways 
of readin' logic levels; it seems to me that an honest, middlin' 
bandwidth, analog 'scope, with a bright green CRT, can do the job, 'jest 
*fine*. I'll take a bank of ten-turn potentiometers and toggles, over a 
click-and-pray virtual test panel, any day.

Uncle Herb

-- 
Herbert R. Johnson,  New Jersey USA
http://www.retrotechnology.com OR .net
preservation of 1970's computing
email: hjohnson AAT retrotechnology DOTT com
alternate: herbjohnson ATT retrotechnology DOTT info



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