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.
Most of the time, when a product is totally dead, an inspection of the power inlet system is the first diagnostic step. I have had a few instances in which the power cord has failed, either at the item itself, or near the AC line plug.
I have also come across those circuit breakers and other protection devices that are made with the same cheap labor and loose tolerances so that they will indeed trip for no valid reson. Of course, there is usually a reason, such as somebody brewing a second cup immediately after the previous one, or the AC power spking up to 128 volts or so, or a momentary drop in the line voltage.
I have also come across items like the Seagate external hard drive assembled with those quite difficult to remove 5-lobe-spline security screws, when the internal exposed power is 5 volts and 12 volts.
It does look like there is a very high level of fear related to steps taken to prevent folks from getting into consumer electronics. Of course it may also be a serious effort to assure that the products are not repaired, but rather replaced.
But for the projector, it was most likely a momentary AC line interruption due to a faulty extension cord connection. Consider that if one part on a circuit board had failed, resetting the breaker would not raise the cost of repairs, since they would consist of replacing the circuit board.
Did the device trip because of an electrical or thermal overload? Understanding what this safety device does would provide valuable information as to why it is undocumented to the casual user. And while the owner's manual did not contain any reference to the device, the service manual probably has information on why the device is there and what may cause it to trip.
Since this is a projector, most likely with a high wattage light source, there is a high likelihood this is a thermal breaker set to open when an over-temperature condition is sensed.The service manual may contain a troubleshooting process that includes checking for blockage of the cooling vents including external clearances, proper fan operation and proper ambient operating conditions.After these conditions are assured, the breaker can then be reset.
If a non-technical user was to know about this reset but didn't know the reasons for it tripping, a potential scenario is that debris such as dust and lint collected inside the device could cause a fire.By requiring at least a look at the service manual, the cleaning, installation and operating environment would be considered before re-energizing the unit.
I've been involved in the design, manufacture and service of both commercial and consumer products for many years and know of a number of situations where certain "features" were not described to the end user out of safety concerns. We always went by the assumption that the end user would toss the manuals aside with the packaging materials and only consult them in the case of a setup problem – operating and maintenance specifications would never be followed. And while we always tried to design the products to be as safe as possible, we could never anticipate the ingenuity customers displayed in abusing our products.
Finally, a true engineer always wants to know the root cause of a failure and not just the fix -- that way you know the fix is truly solving the problem.
Hello Tim! Not an engineer here at all. No formal training in the subject, but I am an avid tinkerer. From washing machines, to automobiles to microwave ovens, I have disassembled more things than you can imagine, and repaired them.
One of my favorites was my father in laws old Telefunken table top radio he had brought with him from Poland. It died on him after several years and he tossed it in the trash. I pulled it out as I loved its wonderful, full, rich sound. I "disassembled" it and started looking around. I found a smoked resistor. After removing it I took it to Radio Shack to find a replacement. They had none and there were no markings. Using an ohm meter and poking around at the remains of the resistor, I managed to get some kind of reading. I then returned to Radio Shack and purchased an adjustable resistor in the range of the one I had removed.
I soldered the adjustable piece in place, fired up the radio and began to tune the resistor until the radio came to life.
That radio has now been on my desk at work for more than 20 years now. It is a constant reminder of how some people will toss something while others will fix it. It's also a little piece of my father in law I have nearby now that he's passed on.
I think everyone is overthinking this problem. If there was a hole in the bottom of the part it had to be included in the design stage, otherwise the tooling, whether plastic mold or sheet metal stamping, would not have included the hole through which you could reach the reset switch. Assume this is a mass produced part, the switch would have to have some sort of mount, a wire path etc. etc.
That stuff would not just magically appear. There would have been a revision so the shop people would have known where to put the hole and on and on through all the steps of production. This is an example of sloppy paper work and not some sinister plot. I am sure we have all followed up on job where someone up the line made an alteration without documenting it properly. That is very common today where management does not see the need for a project engineer to baby sit the product through developement.
The writer of the manual probably never even saw one of these devices in operation and could very well have been minimum wage worker sitting in an off shore sweat shop somewhere with an English language dictionary trying to find appropriate words for a problem he/she knew nothing about.
The likely reason the circuit breaker and reset hole were not mentioned in the owners manual was for safety reasons. The manufacturer might have assumed that a fault big enough to pop the breaker required the unit to be inspected and likely repaired to avoid further damage or risk of fire. This is why some devices have hidden internal fuses, some soldered in place.
Actually, Chuck, I believe the Internet is functioning pretty well in this area. If you run into a problem with a product, chances are, your best solution is to see if others have had the same problem. In recent years, I've found forums are often the best place to do the troubleshooting.
I agree. First things, first. And first, besides checking the fuse, plugging it in, and turning it on, is to check the power supply output. No power, no nothing else.
But it is a bit deceitful to place the reset button in such a way. But clever, also. You sell twice as many in repeat customers who have built a wooden case around it to have it look good. You have to find the same one to fit your enclosure. Clever...
I think for all sorts of repair and refix, first we have to check about the power supply system and the internal saftey fuse. A simple multimeter can be used for these purposes.
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