Well over 30 years ago, as a young TV test technician, I had applied to work for a well-known German TV maker. As part of the qualification evaluation process for this position, I was asked to troubleshoot a newly fabricated set in which a number of faults had been intentionally created. A full set of schematics and appropriate test instruments were provided.
One by one, I had found and corrected a number of faults. Ultimately, all the signals on the CRT socket, including the HV terminal and the deflection coils, were as expected. Yet I still could not get a picture. In fact, the CRT face remained completely dark. Evidently the electron beam was somehow failing to reach the phosphor. One of the common causes of this is a misalignment of the ion trap located on the neck of the CRT. This ion trap consists of a small bar magnet that is typically secured on the neck with a hose clamp.
Moving the ion trap back and forth along the neck and even turning over the magnet did not help at all. So, I was then suspecting that the CRT was actually defective. When I so indicated to the fellow who had been watching over the troubleshooting process, he picked up a screwdriver and showed me that the "magnet" had in fact no magnetization at all! That was something I had never experienced before, nor since, but it was a great lesson about not assuming anything. While I failed to find the magnet that wasn't, I still got the job.
This entry was submitted by Alain Gronner and edited by Rob Spiegel.
After completing an EE degree and apprenticeships in both the instrumentation and the telecommunication industries, Alain Gronner started and ran his own manufacturing company, which developed and produced instrumentation for the US telephone digital network.
Tell us your experience in solving a knotty engineering problem. Send to Rob Spiegel for Sherlock Ohms.
If you could elaborate on your story and send it to me at rob.spiegel@ubm.com we could include it as a Sherlok Ohms entry. If you chose to do so, please send along a short bio as well.
Quite often those of us who have the "knowledge" will assume the problem is of a more complex nature than it may be. But with greater "experience" one can temper the impulse to tear into a problem without first checking on the simple and obvious. Is it plugged in? Are all connectors tight? Is the lens cap off?
The other day I removed a defective device from service and substituted a recently factory repaired unit. That did not solve the problem. Good thing I knew there was nothing wrong with anything else external to the device through previous testing as it turned out to be dud. A second spare worked fine. Now, I could have decided the problem was elsewhere as the spare had been factory sealed and should have solved the problem! Sometimes you have to be prepared for the unexpected.
"The key to diagnosis,however,is knowledge of how the circuit is supposed to work rather than the availability of elaborate test equipment or a degree in electronics" - Eugene Trundle (Author Servicing TV And Video Equipmemt). From that comes knowing exactky what is wrong with a piece of equipment then its just a short step from having it working again,and the most succesful engineers are,(were?),those who have the aility to quickly track down,to componenet level,the root of the cause. This might sound logic or not but its always the best approach to trouble shooting.I mean,why buy a Mercedes when you dont know how to drive a car?
If you could expand on your story here, we could use it for a Sherlock posting. We try to make sure the postings are at least 300 words. You could get there by explaining some of the hits and misses as you tried before you identified the problem. We're always looking for good stories, and yours looks good.
If you're game, please send it to: rob.spiegel@ubm.com
The discussion has called to mind an experience from the late 70's. A system I was working on had two motor driven components (running just under 1000 rpm) and some electronic subsystems that had to be synchronized to the shaft position of each of them. One channel was working fine, but the other was triggering erratically. The shaft position sensor was a bar magnet attached to the rim ofa flywheel and the pickup was a simple coil to generate a pulse when the magnet flew by. We finally (after hours of looking at connectors and cables) removed the clamp that held the magnet, and discovered that the weak signal was due to a broken magnet. Based on the appearance of the broken ends the material was probably alnico, which is pretty brittle. A new magnet solved the problem immediately.
I have never come across a failed magnet in an ion trap assembly.
As for getting into troubleshooting, that is something that I do not only for profit, but also for fun. I have written manuals for some of my employers products with the intention that they would save me from needing to visit some plant and repair equipment.
There are two ways to troubleshoot, the first is to check things until you find something that is not right, and the second one is to understand correctly and in detail how something works, and then look for the part that has stopped working correctly. Actually there is a third method of troubleshooting, which is to randomly replace components until the item starts working again. Of course, that method usually will not correct a problem requireing adjustment instead of replacement.
Over the years there have been a few instruments created to assist by substitution of signals. Many of these are called "Channylists", or some other spelling of the same word. The ads are always interesting, but unfortunately many of them offer little more value than a good multimeter, a circuit schematic diagram, and an understanding of how the item works.
There are things made to assist in finding the points of failure, and some of them are indeed quite useful, although many of them still demand that the service person actually understand the process of the device being serviced. So it would appear that a service career may be secure, until the quality of the products being serviced falls to the point where they are not worth fixing.
I agree, Rob. Skepticism is the right word. Checking if the magnet is manetized is roughly equivalent to opening your car's hood every morning to see if someone disconnected your battery during the night.
I suppose this has become a cliche, but electronic control has made it more difficult for kids to do the kinds of things that we used to do as kids, Alex. Engines and transmissions have powertrain controllers. Brakes are all ABS. Most components -- even down to the catalytic converter -- converse with engine management system. Then there's the issue of lack of space: On old cars we could lay underneath the car, look up and see the ceiling of the garage. Today, the FWD transaxle obliterates all light under there. The bottom line is that you can still work on your car if you're determined, but it's really hard for kids to know where to start. You have to go to school and take a class to get started, instead of just learning by dumb trial and error, as we did.
It takes a deep amount of skepticism to check of the magnet is magnetized, the same kind of mind that looks both ways before crossing a one-way street. There are many cases in life where the obvious is overlooked.
Not much stuff is repairable or even analyzable anymore--I'll second, or third, that comment. Remember when you could fix not only electrical and mechanical appliances, but also your car? And what about all those budding engineers taking apart the proverbial radio and other old-timey electronics? Good luck with today.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 5
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This radio show will show what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
7 
