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!
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.
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.
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).
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?
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.
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.
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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