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Alexander Wolfe
User Rank
Blogger
Re: DeBugging Proto Circuits – Motors
Alexander Wolfe   12/5/2011 5:16:47 PM
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I believe that those of us who went to school in the analog days, when there were labs such as those of which you speak (old style scopes and voltmeters) acquired skills which can't be duplicated in today's digital world. Possibly a lot of the stuff we learned was subjective; the way I put it is, if you've never dealt with 60-cycle hum, how can you begin to understand more complex methods of troubleshooting?

lgrant
User Rank
Bronze
Re: DeBugging Proto Circuits – Motors
lgrant   12/5/2011 3:37:28 PM
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When I was in engine school, some four decades ago, I went to Genral Motors Institute.  GMI was well-funded by General Motors, and had a whole team of technicians who made sure that every piece of equipment in the lab was in tip-top shape.

I then transferred to a smaller, less-well-funded engineering school.  We were taking a Motors course, and were making some unexpected discoveries, like energizing the field on a motor does not affect its running.

It turned out that this school did not have the large lab maintenance team that I was used to from GMI, and about a quarter of the patch cords we used to hook up the motors had opens in the wires.

Our standard routine soon became starting each lab session by grabbing a handful of patch cords and measuring them with an ohmmeter.  After that, our motors started performing much more like how the books said they should.

Rob Spiegel
User Rank
Blogger
Re: The mismarked resistor.
Rob Spiegel   11/15/2011 6:17:55 PM
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Thanks William.

Send me your email when you get the chance.

rob.spiegel@ubm.com

William K.
User Rank
Platinum
Re: The mismarked resistor.
William K.   11/15/2011 5:57:14 PM
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Rob, I have written for Design News before, when Karen Field was the editor. So if those records are available you can learn a whole lot about me. 

I can certainly expand that story, because those two detailers did indeed give me quite a few interesting experiences. In a similar manner, our technical writer created some interesting explanations on several occasions..

But it will probably wait until next week since this week has been filled up by others who made their requests earlier.

William Ketel (you will need my name to find out what I have written.

Rob Spiegel
User Rank
Blogger
Re: The mismarked resistor.
Rob Spiegel   11/15/2011 3:13:04 PM
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Hi William K,

 

I'd like to use your story here for a Sherlock Ohms blog. It's a tad short, but it's a good story. Perhaps you could flesh it out a bit to get it up to about 300 words.

If you're interested, please let me know at: rob.spiegel@ubm.com

I could also use a short bio to include. Twoor three sentences would be fine.

So please send. Thanks.

William K.
User Rank
Platinum
The mismarked resistor.
William K.   11/5/2011 8:07:58 PM
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Several years back I worked at a place where we had detailers to turn our sketches into drawings. One project that I had built up on proto board worked very well, and would be a large coast reduction which also improved reliability.

So after the prototype was optimized I gave the sketch to the detailers, who were a couple of young guys very impressed with themselves. The drawings were then passed to the techicians who wired up the first board, and attempted to calibrate it. After they were unable to get the circuit to function at all, I was called back into the production area to find the problem. I checked some voltages and they were way off. Then I looked at the drawing, and saw that the resistor values just would not work. Back into my office and got my sketch, and found that several of the lower valued resistors were way to high, 27K ohms instead of 27 OHMs. Then I realized that the detailers had assumed that I had forgotten to put the "K" om several of the resistors, and since they were so very smart, they fixed the dumb engineers mistake. I marked up the drawing for the technician and once the correct values were in place, the design worked well. Then I went and explained to the detailers that if they ever thought there was a mistake, they had to come to me and ask about it, rather than make changes themselves. I am not certain that they learned anything though.

shadow1701
User Rank
Iron
Mismarked Resistors
shadow1701   11/4/2011 12:51:34 AM
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I had something very similar happen when I (a ham and commercial licensee) was fixing CB sets for other members of the Rolling Meadows Civil Defense [ESDA] organization.  A very common fault was the carbon resistor in the emittor or cathode of the audio output/modulator active device getting fried so that its value was about 10 to 100 times what it was supposed to be.  In the process, the multiplier color band got fried so it looked like the correct one for the measured value of the resistor.  In the case of one 5-watt transistor walkee-talkee the resistor was supposed to be 33 ohms [orange-orange-black] and it was fried to look like orange-orange-brown = 330 ohms.  The symptom in both tube base stations and transistor walkies was low volume and much clipping.  Some reasonablness checks and voltage measurements solved the problem. Always make voltage measurements and check for reasonable values.

Rob Spiegel
User Rank
Blogger
Re: Not Mislabeled, But Close...
Rob Spiegel   11/3/2011 1:24:43 AM
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Hi Mr.88cet,

You have a good story here.

I'd like to use it as a Sherlock Ohms entry.

Let me know if that's OK. We would like to include your name, but that's your choice.

Please let me know at:

rob.spiegel@ubm.com

Thanks.

Lund_P
User Rank
Iron
Re: Surface mount components
Lund_P   10/20/2011 4:36:01 PM
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I never liked SMT resistors. You can't read them and when you pull one off to measure as soon as a meter probe touches it It’s gone like a tiddlywink never to be seen again. Tape them down helps. My first time seeing a (or not seeing) a SMT resistor I ordered one from the material guy at work he handed me one in a clear bag. The next day I asked for another and mentioned the bag was empty. It was there.  

Now the new color code resistors are very bad. Years ago I purchased my son one of those breadboard kits with springs where you can make a dozen things. I had to get out my DMM and measure the resistors browns violet and reds were especially hard to tell what was what. He quickly lost interest.

 

btlbcc
User Rank
Gold
Surface mount components
btlbcc   10/13/2011 1:33:47 PM
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The surface mount components are probably the biggest ptoblem, both because you pretty much can't hand "wire" a prototype (or limited production) board and also because it's so difficult to read the numbers on them (it there's even room for numbers).

 

But today's leaded components - particularly axial leaded resistors - have their own problems, relating to the color codes.  Some of the resistor manufacturers (sorry, China) seem to have a very odd conception of what the colors are supposed to be (or maybe it's the fault of a heat-curing process for the color bands).  In any event, I have seen orange (and red) that looks like brown and other similar problems.  Getting out the magnifier helps a bit, as does comparison with other resistors ("yes, that's probably orange, not brown"), but ultimately, one has to get out the ohmmeter.  Better a little time spent up front, than time spent troubleshooting and removing and replacing components...

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