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Re: Other lost skills coming back
11/27/2013 4:07:53 AM
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@Duane....Well having got back from work I did just that and got the following.

The E columns indicate the frequency of use of the colours

E3 is the frequency of colors used in the basic E3 values (10,22,47)

E3M is as E3 but with one added for each time a colour is used as a common multiplier (ie black to green) - I thought I would do this as we use these colours as much as the value colours.

And the same for the E6 & E12 series, with and without multipliers.

White is definitely the least used and there is a bias towards the lower colors. but apart from white there's not much in it.

HOWEVER - if you look at E3M, which comprises the most frequently used values, your difficult colours are the ones with Zeros, Duane.  I rest my case!

 Color E3 E3M E6 E6M E12 E12M Black 0 1 2 1 2 1 2 Brown 1 1 2 2 3 4 5 Red  2 2 3 2 3 5 6 Orange 3 0 1 2 3 3 4 Yellow 4 1 2 1 2 1 2 Green 5 0 1 1 2 2 3 Blue 6 0 0 1 1 2 2 Violet 7 1 1 1 1 2 2 Grey 8 0 0 1 1 3 3 White 9 0 0 0 0 1 1

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Re: Other lost skills coming back
11/26/2013 2:55:52 PM
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@Duane - "...blue, grey and white....never managed to stick in my head."

I have the same problem - I thought about it once and I think it is because those colours are the least used in the common E6 series of values - blue and grey are only used in 68, and white not at all.  And really in a lot of cases you only see "E3" values - 10,22,47.  I'd do an analysis of the frequency of use of the colours in E12 but I have to get to work :-(

There's a nice graphic here showing all the E series and how they overlap:

http://www.logwell.com/tech/components/resistor_values.html

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Re: Soldering.....Dry Joints essential knowledge
11/26/2013 2:18:14 PM
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elizabethsimon said: The other failure that I've seen frequently is a solder joint failing due to repeated mechanical stress. Power jacks seem to be especially suseptible to this...

Surface-mount headphone jacks often fail too.  It's a wash as to whether the solder joint fails before the PC board traces peel off.  You really need through-hole.

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Re: Soldering.....Dry Joints essential knowledge
11/26/2013 1:27:33 PM
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@elizabeth  The other failure that I've seen frequently is a solder joint failing due to repeated mechanical stress.

As in cheap equipment that depends entirely on solder to hold a volume control in place.  Guaranteed to last just beyond the warranty period.

Sometimes I think dry joints from hot resistors are just another way to ensure eventual failure and future sales.

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Re: Soldering.....Dry Joints essential knowledge
11/26/2013 1:14:47 PM
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@ Crusty: A good point about the failure of solder joints from thermal stress. I've repaired several older Amatuer Radio tranceivers. In almost all cases, the repair was to re-solder a power component in either the power amp or power supply.

The other failure that I've seen frequently is a solder joint failing due to repeated mechanical stress. Power jacks seem to be especially suseptible to this....

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Re: Other lost skills coming back
11/26/2013 12:53:54 PM
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Zeeglen - For some reason, I still (and always have) need to look up and double check blue, grey and white. Those three never managed to stick in my head.

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Re: Other lost skills coming back
11/26/2013 12:00:20 PM
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Another skill is reading resistor color code without needing to look it up on wikipedia, but sometimes it can be misleading.  Some manufacturers are not overly caring about the quality of the paints they use, often it can be difficult to distinguish between brown, red, and orange even when the resistor body color is light such as beige.

I recently ordered some 4K99 1% resistors made by KOA Speer, when they arrived I had to put one on the ohmeter to verify the value - its colors were green white white brown brown which indicates 5K99 1%.  Then I realized that the first band was actually yellow but transparent to the blue body color, which converted it visually to green.  An almost gotcha.

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Re: Soldering.....Dry Joints essential knowledge
11/26/2013 11:43:44 AM
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Ron - "it is even more useful and important for engineers to know exacltly what a dry joint is, why it occurs, what it looks like and the all the possible consequeces intermittent or otherwise"

So very true. It's quite far from just a matter of turning on an iron and going. Oxidation, surface type, thermal mass - all of those things come in to play.

Fortunately, with a bit of awareness, it can become second nature.

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Re: Other lost skills coming back
11/26/2013 11:39:18 AM
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Crusty - Since I rarely throw things away, I've been having a bit of a field day fixing up broken items I've had buried in my garage. I can't help you with the case though. Mechanical things are not my forte.

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Re: Soldering.....Dry Joints essential knowledge
11/26/2013 10:04:33 AM
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@Ron Neal: I think I can add hot joints to this.

I have come across a number of power packs where the main resistor was not provided with a sufficient heat sinked, or the copper traces were too small for the thermal energy disipated. You end up with a dry joint in the end, but from thermal stress.

One more reason for soldering and repair skills, is in a companies returns department. To get the best quality control a returns department needs to actually tear down the faulty items and feed problems found back into the production cycle. On a number of third part quality audits I have undertaken, the returns process and how it feeds into the production cycle has often been the biggest audit failure.

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