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Someone sent me this photo of a "fake" Chinese 6800 uF @ 50 volt capacitor which was really a 2200 uF @ 35 volts inside. What the Chinese manufacturer did was obtain the outer cases of the larger caps and stuff inside a lower value and lower voltage rated capacitor. From the outside of the cap you would never know what was inside.
On almost all Chinese amps you will never see the plates of the transformers. What they do is place a round or a square cover over all the transformers so you can't actually see the transformer itself. If you tap the the sides of the transformer covers you usually hear a "bong" - hmmmm ... lotta AIR under those covers ...
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Thanks to our fucked up procurement practices we just got bit in the ass real hard here. It was only a matter of time before we were hit with counterfeit components in our instruments. The Spectrum Analyzer group discovered fake tantalum capacitors all over their circuit boards last year. That should have served as a dire warning for the rest of our production groups, but nobody seemed to be paying much attention at the time. Now it’s our turn in this department.
Capacitors began burning off of our PC boards this past week. At first technicians figured it was purely random. Just a few defective parts. Then we experienced a rash of failures across the shop floor all due to the same problem. Surface-mounted tantalum capacitors had overheated, grenading off of circuit boards completely bomb-cratering through half of the board’s fiberglass material. Incinerates circuit traces where a failed part was located. Upon closer inspection somebody figured out that all of these capacitors were counterfeits, made to look like parts from a reliable manufacturer- AVX. Right now we don’t know which company originally produced these bad parts or what is inside of them. This is serious because we have inspected hundreds of our PC boards so far finding fake parts littered everywhere.
We’re in trouble. The instrument line is far behind schedule. If we try to re-work each and every PC board with known good replacement components we probably won’t make our monthly shipments. It’s too labor intensive, takes too much time. Plus there is a risk of causing more damage to PC boards by soldering new capacitors in place. Surface mounted circuit traces and metalized contact pads are delicate. We can’t knowingly allow instruments to ship to customers with fake components in them, either.
Situations like this are created by a long chain of events, most of which should be avoidable. Employees who are parts buyers maintain inventory levels and purchase components from vendors. The parts buyers are rewarded with incentives like bonuses for keeping their inventory levels as low as possible and for locating inexpensive materials. Parts buyers scrounge around for bulk purchases at rock-bottom prices. In the meantime, component manufacturers always end up with an amount of scrap parts. No matter how tight their processes are, they always have some material that does not meet specifications. Rather than reclaim or recycle their defective components, companies sell off those inferior parts at a fraction of cost. That way they don’t have the headache of recycling on their own and they still make some money. Most of the time these bad components eventually make their way to China.
Chinese electronics companies take these bad components and remove the part’s markings which indicated the original manufacturer, component value, and date code of production. Then each part is re-marked as if it was brand new. Initially the processes used to counterfeit high quality components was rather crude and easy to spot by a seasoned technician. That has changed considerably in the past couple of years. Knock-off parts generally had their top surface ground down just enough to remove markings. They were hand painted or inked which looked sloppy. Scratches were always clearly visible like the parts had been dragged across sand paper, and their edges were frequently rounded off instead of clean and sharp. Tell tale signs of being altered. These days fake components are laser-etched by machines making them much harder to identify.
After being repackaged as new stock, counterfeit parts are put up for sale at ridiculously cheap prices. And that’s where our clueless parts buyers come into the picture. They think we’re getting a great deal on bulk high quality parts not even suspecting for a moment the components they are buying might be fakes.
Capacitors are used in just about every aspect of electronics. Primarily they are utilized to store an electrical charge at a certain voltage and then discharge at a constant rate. They are commonly employed to take an electrical charge that might be dirty with power drops and spikes. A capacitor can handle power fluctuations like that yet still discharge clean and steady as if it was a filter. There are many different kinds of capacitors. Electrolytic caps for example use wet chemicals to store voltage. Lately we have been using Tantalum capacitors extensively in our products. Tantalum is a rare metal with an interesting property- it can self-heal somewhat if it is weakened or damaged in a capacitor. When they finally go bad though, a tantalum cap usually will overheat to such an extent that it pretty much explodes off the PC board destroying it in the process.
xover 發表於 2012-3-13 18:52 http://www.post76.com/discuss/images/common/back.gif
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