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Sherlock Ohms

The Ghost Image Messed With the Display

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warren@fourward.com
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Re: Good logic
warren@fourward.com   11/15/2012 5:38:21 PM
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I think the one-change-at-a-time rule should be written into law,or at least a physical punishment given for ignoring it. The little or much time given to its implementation pays off more than we know!

Tool_maker
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Re: Good logic
Tool_maker   11/15/2012 4:20:19 PM
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Battar: I think you need to add a corollary, only change one thing at a time. It drives me crazy when someone makes wholesale changes that make the problem worse and then they cannot recall everything that was done so we can reverse the procedure to get back where we were and start the trouble shoot process anew.

Rob Spiegel
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Re: Good logic
Rob Spiegel   11/8/2012 11:32:44 AM
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I agree Battar. Hitting the product can be a real solution. I had a TV for a few years that needed a smack on the side every time it was turned on in order to bring up the picture. It was quite amusing to watch my kids each morning as they turned on the TV, and then smacked it on the side.

Battar
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Re: Good logic
Battar   11/8/2012 2:08:54 AM
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Rob, thats 97% for one of the 4 options. "hit it" is good for 30% - it cures bad connections and cold solder joints fast (but temporarily). As one of my colleagues was fond of saying, a fault isn't a rabbit - it doesn't run away, it always returns (that rhymes in the local lingo here).

Rob Spiegel
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Re: Good logic
Rob Spiegel   11/7/2012 5:02:26 PM
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Battar, did you mean that 97% of the time one of the four attempts works? Or did you mean that 97% of the time it's the number four try (looking at what you touched last) that delivers is the solution?

SteveG56
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Iron
Re: Good logic
SteveG56   11/7/2012 11:08:26 AM
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You're right, Batter.  And I think the 97% statistic for step #4 is pretty close.  In this case the problem was on a board 5 slots away on the backplane and some time had elapsed since the previous design change.  Regarding the pesky spread spectrum clock oscillator, we were probably thinking if a little is good, a lot will be better.

Battar
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Re: Good logic
Battar   11/7/2012 9:25:15 AM
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Steve, actually you just had to follow the 4 rules of fault-finding for technicians. It's under rule 4. The rules are - 1)Turn it off, turn it on again 2)hit it 3) read the data sheet 4) look for the problem at the last place you touched before it stopped working. That usually solves 97% of all problems.

Charles Murray
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Re: Good logic
Charles Murray   11/6/2012 6:08:54 PM
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Great sleuthing work, Steve. I agree with JamesCAnder's comment below: "...intuition and experience can solve a lot of issues."

Rob Spiegel
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Re: Good logic
Rob Spiegel   11/6/2012 5:57:54 PM
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Yes, I know how that goes, Steve, when you think the problem is in one area and it's acually in another area.

SteveG56
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Iron
Re: Good logic
SteveG56   11/6/2012 5:00:44 PM
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You're exctly right.  The thing was, the first spread spectrum clock oscillator (I'm not a fan of those) had a narrower "spread" and didn't cause the problem.  It was when we widened the spread, to get the emitted noise spikes lower, that the ghost images started showing up.

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