HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
REGISTER   |   LOGIN   |   HELP
Comments
View Comments: Oldest First|Newest First|Threaded View
Page 1/2  >  >>
Beth Stackpole
User Rank
Blogger
Following the trail
Beth Stackpole   2/27/2012 7:06:25 AM
Sometimes knowing too much and exploring too many options masks the simplicity of the real problem. By asking the basic questions and doing the due diligence in terms of the general state and maintenance history of the oscillator, you would have been on the trail of the problem much earlier. But you're absolutely right that it's always easier to come to this conclusion in hindsight. How come we never learn??!!!

Tmachell
User Rank
Iron
Re: Following the trail
Tmachell   2/27/2012 8:05:48 AM
NO RATINGS
We never learn, because we keep forgetting what we learned last time. Afterall, we're only human right? Thanks for the comment Beth.:-)

Rob Spiegel
User Rank
Blogger
Re: Following the trail
Rob Spiegel   2/27/2012 2:07:51 PM
NO RATINGS
Looks like the solution came from not taking anything for granted. Over and over with these Sherlock Ohms problems and solutions, the answer comes when the most simple (and thus invisible) assumptions are challenged.

Tmachell
User Rank
Iron
Re: Following the trail
Tmachell   2/27/2012 2:56:20 PM
NO RATINGS
Thanks Rob. There is truth in what you say. Perhpas the article should have been "Assume Nothing" when trouble shooting. - Tom

jmiller
User Rank
Platinum
Re: Following the trail
jmiller   2/27/2012 8:09:56 PM
NO RATINGS
One of the first things that jumped out at me was the comment about being "in tolerance."  Sometimes I find people that are looking to make a change to this or that for whatever their personal reason/goal is and all they care about is if the parts are "in tolerance".  What happened to wanting to make sure the end product was of good quality and made as cost effective as possible?

Phil Hobbs
User Rank
Iron
What you needed was an analog scope!
Phil Hobbs   2/28/2012 9:29:38 AM
NO RATINGS
A classical example of how misleading digital scopes can be. 

An analog scope wouldn't have hidden the problem--you'd have had a broad stripe across the display at low sweep speeds.  When using digital scopes, I leave them in "envelope" mode most of the time, for just that reason.

Cheers

Phil Hobbs

oldtimer8080
User Rank
Gold
This example is why digital scopes are BANNED in my lab!
oldtimer8080   2/28/2012 1:00:48 PM
NO RATINGS
As a Calibration Tech for AMD in the beginning of my career, I had seen these problems easily with my analog scopes.

When I worked at Cray, I saw and dealt with SAMPLE and HOLD issues at the GHz level. Issues with the plug-ins for  the 7104 to work with greater than 1 GHZ levels were always a problem. Intermittent and harmonic static had to be captured and NO trigger was fast enough!

Today, I ONLY keep analog scopes. The noise may show up as a blur, but that is still better than the scope " proving " that no noise exists...

That " Sample and Hold " issue is the ugly secret that today's scope makers ( including Tektronix ) won't talk about.

The real irony: It cost Cray ~$60k for the 7104 & the plug-ins. That was in 1980s $.

It costs around $1k for the same stuff today. Just spend another $1k to get it recalibrated. New is not always better. Old warhorses still kick @$$...

I've already collected my stuff. Have at it on eBay....

 

Jon Titus
User Rank
Blogger
Re: This example is why digital scopes are BANNED in my lab!
Jon Titus   2/28/2012 1:49:28 PM
NO RATINGS
Good point about analog scopes.  I cherish my older Tektronix 465B, which I bought on Ebay years ago and had calibrated and a few components replaced.  Love that scope.  Recently I had to help troubleshoot a signal source.  At first it looked OK, but when I stepped through the time/division-switch settings it was obvious the oscillator had noise on the signal. Turned out that the power-supply filter was bad and let 120-Hz noise modulate the oscillator output. I find if I don't look at signals on all of the frequency settings I can miss problems that don't appear when I "think" the problem exists elsewhere.

Island_Al
User Rank
Gold
Instruments readings != word of God
Island_Al   2/28/2012 5:28:10 PM
NO RATINGS
Been there, done that.  I use the LFW (Last Fiddled With, or at least thats the "nice" version of it) method in evaluating problems.  How many times have we all heard "oh yes, I did so-and-so, but that had nothing to do with this problem"?

And not just o-scopes, but in my old age I take no readout as the word of God.  A very recent example is one of the staff engineers told me an eight watt air to ground radio was outputting 1 watt and had a 1/4watt reflection using a Bird watt meter.  It came back from the repair facility no trouble found. I measured it myself with an attenuator and spectrum analyzer and found full power.  He used the wrong slug in the meter! 

Also I get a kick out of the guys here who use 1 hertz resolution on a 500MHz signal, then have the nerve to tell me "the oscillator is off frequency by 1234Hz."  I pull out the spectrum analyzer spec on freq drift/accuracy.  I get the "Gee, I never thougt about that." answer.  Same with the LSD on digital meters.  Read the accuracy specs!

Had a non-tech guy yesterday come in an he reached out to touch a circuit card I just fixed.  I told him "Don't touch that or you'll get hurt."  He asked "Will it electrocute me?"  I replied, "No, its low voltage, but if you break it I WILL HURT YOU!"!

I love my digital instruments, but have to learn their limitations.  Great story, one that I have lived countless times over the past (almost) half century.

Tmachell
User Rank
Iron
Re: Following the trail
Tmachell   2/29/2012 7:43:35 AM
NO RATINGS
In this regard, "being in tolerance" means passing the automated test. The test can't move forward if the UL or LL are exceeded.

Page 1/2  >  >>


Partner Zone
Latest Analysis
Eric Chesak created a sensor that can detect clouds, and it can also measure different sources of radiation.
Festo's BionicKangaroo combines pneumatic and electrical drive technology, plus very precise controls and condition monitoring. Like a real kangaroo, the BionicKangaroo robot harvests the kinetic energy of each takeoff and immediately uses it to power the next jump.
Practicing engineers have not heeded Yoda's words.
Design News and Digi-Key presents: Creating & Testing Your First RTOS Application Using MQX, a crash course that will look at defining a project, selecting a target processor, blocking code, defining tasks, completing code, and debugging.
Rockwell Automation recently unveiled a new safety relay that can be configured and integrated through existing software to program safety logic in devices.
More:Blogs|News
Design News Webinar Series
3/27/2014 11:00 a.m. California / 2:00 p.m. New York / 7:00 p.m. London
2/27/2014 11:00 a.m. California / 2:00 p.m. New York / 7:00 p.m. London
12/18/2013 Available On Demand
11/20/2013 Available On Demand
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Apr 21 - 25, Creating & Testing Your First RTOS Application Using MQX
SEMESTERS: 1  |  2  |  3  |  4  |  5


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Next Class: April 29 - Day 1
Sponsored by maxon precision motors
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service