When my wife and I got married, we bought a house in the Phoenix area that came with a solar water heater. Almost all new houses came with solar water heaters during those days due to various government credits. After a few years, when it was just a month or two out of warranty, it stopped working. A little debugging with a volt/ohm meter and some jumper wires revealed that all the components in the system were working except for the controller. The pump would pump when connected to power. The thermal sensors were producing values that seemed reasonable.
So, I did what seemed the only sensible thing -- I took the controller out with the intention of taking it to work for further debug. My wife, however, was skeptical that I would be able to fix it. I was sure any repairman would junk the whole controller rather than debug it to the component level, which is what I intended to do.
The guts of the controller were made up of an inexpensive single-sided PCB that used op-amps, resistors, and diodes to perform basic logic functions (for example, if the water in the collector is warmer by a certain amount than the water in the storage tank, turn on the pump). These days all that would be done with a microcontroller.
I traced a schematic of the board and broke the resulting circuits down into analog and logical functions to learn how it worked and to help find the fault. During a visual inspection, I could see a couple of diodes that were obviously charred. I analyzed the circuit performance and discovered that they were very underrated for the current they would have to carry when forward biased. Further bench testing confirmed they were toast. I removed them and replaced them with higher-rated diodes from lab stock and buttoned everything back up.
That evening, when I put the controller back into the system, it began working again. It continued to work until we sold the house a few years later. As a relatively new engineer, it was a boost to my confidence to be able to fix the controller, especially since I avoided what would have probably been a $200 repair bill by replacing components that only cost a few cents. It also reinforced the lesson that components have specifications for a purpose, and violating those specifications has consequences.
This entry was submitted by John Roe and edited by Rob Spiegel.
John Roe has a master of science in electrical engineering from Georgia Tech. At the time of this story, he was working for a medical electronics company. Currently, he works for a semiconductor company designing high-performance networking and computing ASICs.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
I had a similar problem with the controller for a double oven. When the manufaturer's repair guy came out he told us the control unit was no longer produced. We would have to reaplce the over. This was a $2K+ proposition. Oh, and by the way, the new units were slightly larger, so the hole in the cabinetry would have to be enlarged, if possible. Sounds like a way to make work for the contractors. I took the unit out and confirmed the problem. I isolated the problem to some power transistors. Rather than fixing it myself from that point I found that there were several companies that would refurbish the units. One was a short drive from home. So, I took it there and they fixed it. It has worked ever since.
This controller sounds very alike the technology that I saw in the Luigjes Hottop solar boiler which I installed in my home (in the last century ;-). Including the single sides PCB and dual comparators. Only this one controlled the pump via a relay contact, so there was no high current through the electronics.
Its operation was extremely simple and I doubt that even today you'd find a digital controller because the analog controller was so simple. Maybe just for calibration purpose it would be made digital (and to allow the boiler temp to be displayed so the user would have a nice display to look at instead of the two LEDs on the original controller.
The function of the entire controller was executed by the two comparators:
1. Is the temp of the solar panel a set amount of degrees higher than the water in the boiler? If yes, switch the pump on.
2. Has the temp of the solar panel reached close to boiling? If yes then switch the pump off.
The first comparison guarantees that only energy (hot water) will flow into the boiler, no hot water will cool down in the panel without the sun shining. The second will avoid the water getting pressurized from steam production and the boiler be damaged. The solar panel may get (very) how without water in it (NOTE that there was a quantity of air in the system that normally filled the solar panel when the pump was off - that protected the system so it could not freeze or boil). When the pump engaged, the panel was filled with water and the air moved to either the return-flow pipe or the designated container in systems with large height difference between boiler and panel, like in my system.
The calibration required for the controller were two potmeters to set the temp difference between boiler water and panel before the pump turned on and the max temp of the panel before the pump was turned off again.
The system was very simple and reliable and I enjoyed it for many years until I sold the house. I still plan to go back and ask if it is still working - I left a spare controller just in case.
I designed and built a solar hot water controler back in the early 80's. It is also of analog design and built and tested to UL standards. I built a total of 50 units, all of which are still operating (to my knowledge) to this day. No one has complained. Several of them, including mine, had to have the wires to the panel sensor replaced due to UV damage. The pump is controlled using a TRIAC in place of a relay. Troubleshooting and replacing defective components is easy on the double-sided board, and parts are still available to this day.
Sounds very similar to the system I fixed. I think there may have been one other logic circuit that would run the pump if the temperature in the collector got too close to freezing. I don't recall (or didn't notice) anything that would drain the water out of the collector to prevent freezing, so heating up the collector during the very rare occasions when temperatures got very low (this was in Phoenix, after all!) seemed like a reasonable compromise, I guess.
Of course, this was all 30+ years ago, so my memory of some details has suffered "bit rot" over the years!
The older style controller that used analog components was indeed repairable, which is the main reason that units made now are digital. Harder to troubleshoot and six months later you can't purchase the controller chip if you wanted to. Also, they would be programmed and the only source of the programmed controllers is the manufacturer. And by the way, they don't sell just the controller chip.
We had a similar failure on a Sears microwave oven, in that the failure was an opto-isolator that drove the power switch, but the only recourse was to replace the whole circuit board at a cost equal to the price of a cheaper replacement oven. Not as many features, but would you pay $250 to repair a microwave oven?
I've lost track of all the non-user-serviceable products and components I've fixed.
There was the PC motherboard which wouldn't drive the printer. Had to replace a surface-mount IC on it.
The 1984 washer that was incredibly robust but stopped working in 2008. It would never progress from the washing cycle to drain, fill, and rinse. The controller board would have cost $350, except you couldn't even get them. The triac which fixed it cost 37 cents from Mouser.
Two Roombas, each of which had failures in the battery charger. Each took two surface mount transistors (didn't bother to figure out which one had failed).
The loss of innocence of my son, at about age 12: "Dad, this stereo receiver is dead. It won't go on. Nothing at all." "Son, get a #2 Phillips screwdriver from the workbench." "Dad, the label says 'No user serviceable parts inside.'" "Yes, son. no user serviceable parts inside." as screws are removed from the cover. "Son, no user serviceable parts inside," as the cover is lifted off, revealing a blown glass cartridge fuse in clips, in plain sight at the top of the unit.
My son is now 37. I'm still using the receiver, haven't had to change the fuse a second time yet.
The $1.50 picofuse that put the $200 laser printer back into service in 2005 or so. Still using it.
There are dozen more instances, but they all follow the same pattern. If you simply think a little, you can replace inexpensive components instead of expensive assemblies or complete products.
We'd love to use some of your stories at Sherlock Ohms postings. Could you send one or two of them along? They need to be at least 350 words, and we also need a shor bio to go along with it -- about two to four sentences would be find.
I forgot to mention the Mitsubishi ECM (car engine control module "computer") which needed four inexpensive capacitors and some jumper wired where PCB traces had been eaten through by poorly-selected capacitor adhesive. That baby would have cost $700, had I not been able to install about $4.75 worth of capacitors.
And the dishwasher control which was over $12, but not available, fixed with a couple of "bullet" connectors costing pennies.
And I already promised to write you about the GM high-mounted brakelights. They will have to be a destructive analysis. I tried to open them to effect a repair but they were bonded (ultrasonically welded? epoxied?) so well that I will have to break them apart to find out what failed.
Terribly busy right now--besides my day job I'm leading the volunteer recovery effort from the tornados which struck here on April 16, 2011. This consumes all my nights, but it's nearly done. I should be able to send you something in May or June.
Back in the day, with Sams Photofacts and MCM Electronics there was nothing you couldn't fix.
I've gone through a series of preferred sources over the last 50 or 55 years, as each one gets "commercial focus" and establishes minimum order levels too high for hobbyists. Allied and Newark were great when I was a kid, but now the $50 or $100 order makes them unfeasible sources for a couple of transistors or capacitors. My current favorite is Mouser.
Radio Shack was a good place to go, but you had to give them your phone number and address every time you bought something in the store. Now, Amazon.com actually has a good supply with no ship minimums.
Radio Shack is okay for 10% resistors and a few transistors, but I find that I often need capacitors rated for the military temperature range, for use in the outdoor heat-pump or under the car hood. Radio Shack only stocks commercial grade capacitors, not military grade, even though the military grade units cost only a few cents more.
Larry: The "problem" with your logic of checking inside and replacing defective components is that you are denying the refuse collection technicians (garbage men) there right to make a decent living by picking up all this "junk". Furthermore, the landfills would not be nearly as filled, since a picofuse or SMT transistor occupies far less space than an entire stereo system. And, IF that's not enough to spur your patriotic juices, how about all those Chinese assembly line workers that could be furloughed because YOU did not purchase a new $500 stereo ...... instead replaced a 37 cent part??????
I'm watching my favorite program and there is a knock on the door. My neighour needs leads for his multimeter. I lend him the whole Harbour Freight special with clamp on ammeter with a breif explaination.
Then I think, he knows enought to to pull the plug, right. He is trouble shooting his electric dryer. I had to check. Yes, he knows. We looked a lot of the part. The schematic used non standard symbols but we figure out what was what.
I mensioned that what works is as important was what does not work. It does not do any thing. Oh, yes the door light comes on and the clock works runs. I showed him how to jumper around components. I explained the schematic some what. With a half hour we found the thermal limit component that we jumped allowing the other phase to power the motor.
He went on line and found the component. He phone a friend in the business who had the part. He replace the part and had the dryer running about an hour and half after I started.
He thinks I should go into the business. I think it could never pay enought fixing things rather than Oh its broke and cant be repaired I'll sell you a new one. Just too honest. An not worth my time. But it was fun.
Reminds me when I had a VW Diesel Rabbit. The car ran well, but one time a water leak got in the glow plug time delay relay. It failed and I had to lift the hood and apply a jumper between the battery and the glow plug bus for 30 seconds or so to get the car started. I checked the VW dealer and a new plug in relay was $35 a lot in 1985. So I took the old relay apart, and replaced the comparator ICs, which cost less than $1 each, but with shipping ended up costing $4. It was good for the rest of the car's life.
I had a simular experiance with my solar pool heater. The controler stopped working, I removed the controller from the circuit and found the power relay tha operated the water valve was defective. I went on line to find the part. The venders had a $50 mimium order so it was prohibitively expensive so I bought a new control;ler for $100. Problem solved!
Waah. It was a professional development learning experience. The company benefits from this type of learning of its professional staff. You ought to see what constitutes work for executives when they have their corporate retreats.
Well, I did the work at lunch, so no loss there. The company was founded by a bunch of ex-HP engineers, so they encouraged use of lab stock for private projects (within reason, of course) as had been the practice at HP back in the day. It's amazing what you can learn (that they don't cover in college classes) by fooling around with stuff!
Later on, several of us built Z80-based CP/M computers with parts from lab stock, with the company's blessing. We learned a lot about firmware (from fiddling with the BIOS) and microprocessor-based design from that project that we leveraged into user interface and feedback control systems in our products. In one example, I used that experience to design and build a Z80-based test set for testing the image processing boards in the system. The company bought a lot of experience for its engineering staff with a couple hundred dollars of lab stock parts!
I'm still encouraged when companies like Google encourage employees to work part time on similar projets. It's nice to see G-job culture live on!
In our throw away society there are many products out there that are discarded for want of a $2.00 part. I have a background as a Machinist as well as in Electrical technology and find that many times some simple, impossible to fid part is the only problem. Fortunately I can go out in the shop and use my small lathe and mill to make a replacement part. It might take me several hours and would seem to not be cost effective, but when I have some time and no money that part I am able to make is a real life saver. Just think how much money is spent because almost no-one anymore has any idea how things work, and thus they don't know that it could be repaired.
A $150 repair avoided to a television for a board that I was able to obtain for $25, deliverred. The thrown away lawn mower that I was able to fix for $12 worth of parts after cleaning the carbon out of the cylinder and installing a new air filter.
And we have a generation that are growing up now that have never taken anything apart and put it back together. Hand them a screwdriver and they stab themselves, a wrench and they smash their finger... And they say wonderful things like "You fixed that? I just threw mine away and got a new one..." And then they wonder why they owe so much on their credit card.
I think young people are apt to replace a product rather than fix it for a number of reasons. They've been taught by brand owner to replace rather than repair. Most kids don't know how to replace the battery in an iPod. When the battery goes, it has to be replaced. By the time a TV goes, the consumer is so far behind on features, there is no reason to repair the old TV. In fact, TVs are getting replaced before they go bad because of the new features.
Excellent analysis Rob and Kf2qd. However, whenever I'm in similar discussions that one thing that is asked is "And how long did that take you?", which is often followed by "Well, if you make $xx an hour at your job, along with all your benefits...and my free time is worth more to me than that!"
Excellent ploint, Jack. I've often used that calculation to determine whether to do something myself or hire a service company (giving the bathroom a good cleaning is a good example). But repairs to an applicance come with an additional consideration. Fixing a dishwasher or dryer means I don't have to send this big lump of stuff to a landfill.
Don't get me started on the stuff I've had to send to the landfill because it couln't be repaired! I've sent probably a dozen of my kid's CD players to electronic recycling (not the landfill, fortunately) all for the exact same reason: there was a tiny plastic tab that held the clamshell case closed and that tab broke off. Usually it was lost forever, but even if I had it I couldn't find a glue that would make a permanent repair. Everything else in the player would work fine, but the lid wouldn't stay closed.
While saving up for a new one my daughter did her own temporary fix: a big rubber band to hold the lid closed. Not pretty, but it worked.
Eventually the solved the problem of breaking CD players permanently: they got iPods.
I know exactly what you're talking about , John. My daughter has a desktop CD player with a lid that won't stay closed. She thought she needed a new one. I gave her a rock to set on top of the lid.
What's the worst that can happen? If I take it apart and can't fix it after spending a few hours/minutes, what have I lost? Just the time. I may have just saved me a lot of money fixing something instead of replacing it.
When something breaks/stops working, I always look at it with the intention of at least trying to find an obvious problem. Blown fuse, etc.
I had a problem with my apartment A/C running and not cooling sufficiently. I borrowed an Agilent datalogger from work, along with a number of thermocuples. I monitored the temperatures in and out of the FAU, logged the compressor on signal. I was able to show that it wan't cooling properly. The head maintenance tech complimented me on the charts that I showed him the demonstrated the lack of performance. "You've done your homework". Ended up with a new compressor out of the deal.
Good for your for documenting the problem, Bobl. Do you think that made the difference in getting the new compressor? Perhaps if you hadn't documented it, you wouldn't have been taken seriously.
In this case, my electric bill went from about $50 to $200 in a month. Yes, I was able to show that the unit would run for hours and not cool down the apartment. The weather wasn't even very warm yet. The most telling chart was when it tried to cool down the apartment from 74 to 70 degrees in the evening when the outside temperature was lower than 70. Yes, I could have opened a window, but that would have defeated the reason for all the monitoring. It took 6 hours (6pm to midnight) to cool it that day, all duly noted.
Unrefutable documentation is the way to go. He really couldn't argue with the numbers.
Thus continues the cycle of throw-away, by looking only at the cost and not recognising the value of being able to understand the operation of and fix the product yourself - which is a great motivator and pride factor, too often misunderstood - as well as the value of not adding to the waste stream.
Another factor often not considered is that people will not spend a few minutes to fix something because they consider it not worth their time, only to take hours and drive all over town to shop for the replacement. How crazy is that?
One totally ridiculous part of American culture seems to be to spend several hours every month or so, either to have the oil in the car changed (which apparently is done unnecessarily every 3k miles) or to go to the tire center to have a rotation. Each of those visits includes time to make an appointment, go to the center at the scheduled time; have a friend pick you up again or sit in a non-descript waiting room for around an hour; if required pay for the unnecessary service and drive home again. Each instance costs you anywhere up to two hours and when asked, everyone will give you their version of why they have no time or not want the hassle of changing oil or rotating tires - while you can do that at home in about 15 mins: you save time, you save money and you *know* that the work is done. How is that more hassle than wasting 2 hours, hoping that the work was done and paying for the experience?
I know - fixing a tricky appliance can involve a lot of time, possibly result in a still-not-working device and other frustrations, but the times that you can get it to work and often, by understanding how it works, actually make it better, is priceless experience in my opinion.
BTW, if you have time to answer (or even read) this post then you don't value your spare time that high.... ;-)
Good point, but I don't have billable hours so I don't explicitly earn more for spending a couple hours more at work as opposed to fixing something myself. Working extra might lead to more money when it salary evaluation time if my extra work results in doing something useful that gets recognized by management, but that's not a given.
Plus, there is something intensely satisfying about fixing something, or even just knowing you could if you had to. I recently helped my daughter experience that when I walked her through how to re-light the pilot light in the furnace in her apartment one cold evening this past winter. Otherwise she would have had to wait until the next morning when the maintenance people showed up. She said it felt really good not to have to depend on them any more!
Plus I really enjoy it. I work all day on a computer; when I leave at the end of the day there's nothing to point at and say: "I made that today". I just push bits around on a hard disk somewhere, so working with my hands is a kind of therapy. Now I know that's cheaper than seeing a therapist!
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