My church’s data projector stopped working, and since I was known to be an electronics engineer, I was asked to take a look at it to see if it could be fixed. The symptoms were very simple. You applied power and nothing happened -- no power, no LED, nothing.
I searched the manual and troubleshooting guide which told me nothing more than to turn the power on. The remainder of the troubleshooting section assumed the power was on and the unit was responding to its remote or buttons.
I decided to dismantle the unit. The assembly appeared to be designed neither for ease of assembly or disassembly. It seemed to be assembled by very cheap labor, where the cost of assembly was not a significant portion of the overall cost to manufacture the projector. After I removed the covers, the main board, the rear interface panel, and the cooling fan assembly, I was able to remove and check the input filter -- It was OK.
The next suspect was the power supply. With great difficulty, I managed to remove it and partially dismantle it to the point where I could unplug the input power cable and check to see if there was power. There was none. Obviously, there was a break between the filter and the power supply. Then I noticed, mounted to the bottom of the case, a suspicious-looking device with the power leads running through it. I removed it and discovered that it was an undocumented, resettable overload switch that was accessible through a small hole in the base of the case. When I pressed it, it gave a reassuring click and power became available at the power supply connector.
I decided to take a chance that this was the only problem and reassembled the unit. It worked perfectly again. I have to wonder how many units have been thrown out needlessly and how many customers have been charged exorbitant fees for repairs when the fix required the serviceman to simply poke a pin through a hole in the base to reset the switch.
This entry was submitted by Bill Washington and edited by Rob Spiegel.
Bill Washington has worked as an electronics design engineer in telecommunications and general electronics for more than 20 years. Prior to that, he spent more than 10 years in electronic equipment installation, repair, and refurbishment.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
I love hearing you comment your code. I was a design engineer for many years; some of the work I did involved writing VHDL for FPGAs. As I became more senior I was involved with overseeing other designers as well as reviewing design code. Kind of a funny story made short which involved me overseeing 32 poorly structured VHDL design files owned by foreign division of the company where I was currently employed. Whenever the engineers made changes they would comment ALL the old code and insert new code and very rarely many any comments of importance. I'm like do they really understand the concept of commenting your code? So they is why when I teach a class on FPGA using VHDL at the university I always stress the importance of GOOD Comments. Just as you said Nancy you may have to come back to this code at a later date. Also, good comments make it easier for you if you ever have to modify someone else's code.
Funny you said, "Also, good comments make it easier for you if you ever have to modify someone else's code" because I always thought so too, which is another reason why I commented mine - for anyone else down the road or for test sets that were moved to our plant in Mexico (which made it easier for them and prevented me from having to travel there to fix things). But I knew some engineers who wouldn't comment their code on purpose - they viewed it as job security. They figured that they would have to be called in to troubleshoot any problems because no one else would be able to figure out what the code was doing. A very bad attitude but when you are working in an industry where lay offs are common place, I could see how it would evolve.
I know these people. Job security went out many years ago. I find that type of attitude can work against them because they may be viewed as difficult to work with and may be on the layoff list because of it. They need to realize there is always someone else who can do the same work as them. While it may be hard for the company to recover but not impossible. So while they make it difficult for Company X, they may be burning their bridges with Company X and potentially other companies as well. Just like you said layoffs are common and person at Company X today may later be your interviewer at Company Z tomorrow.
'course on the other hand, if the reset button was at all visible, a natural curiosity might have simply pushed it PRIOR to disassembling the unit.As a young child, I remember how IMPRESSED I was with my mother when she simply pushed the little red button on the bottom surface of the In-Sink-Erator, and the darn thing roared back to life! How simple to reset a garbage disposal !! – Often, development EE's request the same reset button on the pre-production prototypes I've helped create.
I think in power supply issue, it's always better to check the saftey fuse unit also. In most of the power supply issues, what I had seen is the fuse unit got damaged and blocks further power supply.
The undocumented circuit breaker (likely a "Supplimental Protector") may have been the result of a failed safety agency test. When the abnormal tests and fault tests were performed, an unacceptable result may have been addressed by adding the reset device. The resetable device may have had too much variation for the application or not have been up to the handling or operation requirements of the end product. As for the instructions, the omission may have been to prevent a user from constantly resetting the device and causing the protector to fail with the contacts closed and create the hazard presented by having no device.
The blogger who suggested that this "safety cutout" was an afterthought to clear the U.S. / Canada safety agencies was probably dead nuts on target! However, IF they became aware of the need for such a safety overload protector, and had to add it to the BOM, there's no reason why they could not have also added a small stick-on label indicating its presence. To not do so IS, in my opinion, a demonstration of complete unethical behaviour!
The folks who commented about "commenting" their code, no matter what language or environment ARE also dead nuts on target. When I started out many decades ago, the first "languages" I learned were AUTOCODER, RPG & FORTRAN on I-B-M 1401 & 1130 computers using Hollerith cards to input the code & data. Practically EVERY single card of the "program deck" had pencil comments on the back side of it. I've been profusely commenting ALL my code to this very day, regardless whether it is ASSEMBLER, BASIC, C, PASCAL, or LADDER! I KNOW that I am replaceable, and have never been of a mind that what I've done cannot be diagnosed by someone else. Any engineer, programmer, etc. who has that mentality is a disturbed person.
How do you tell lazy, dumb, and greed apart? I have had major problems with the manuals that came with several Kenmore appliances. They don't tell you very much, and what they do tell you is not clomplete or clear. There are also no aftermarket repair manuals around any more.
I had a freezer stop working, and the troubleshooting section of the manual did not describe the error code on the digital display. I finally got help by looking at several websites and made some sense of what I found. The Kenmore manual said that some models had a 9v barrery. However, it did not say where the battery was located. The website said it was at the bottom, front of the unit. Changing the battery solved everything.
This was not an add-on item. I have no idea as to why the manual did not have clear information about this. Did Sears want me to have to make a service call?Did the person who wrote the manual know anything about the freezer? Did anyone who knew about the freezer proof read the manual?
How do you tell lazy, dumb, and greed apart? I have had major problems with the manuals that came with several Kenmore appliances. They don't tell you very much, and what they do tell you is not clomplete or clear. There are also no aftermarket repair manuals around any more.
I had a freezer stop working, and the troubleshooting section of the manual did not describe the error code on the digital display. I finally got help by looking at several websites and made some sense of what I found. The Kenmore manual said that some models had a 9v barrery. However, it did not say where the battery was located. The website said it was at the bottom, front of the unit. Changing the battery solved everything.
This was not an add-on item. I have no idea as to why the manual did not have clear information about this. Did Sears want me to have to make a service call?Did the person who wrote the manual know anything about the freezer? Did anyone who knew about the freezer proof read the manual?
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