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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Advent Powered Loudspeaker and counterfeit transistors
Kudos to you Mark, and others, that are inquisitive enough to closely
examine faulty/counterfeit parts, and report the incidents. The previous instances of fake components that I've heard about were epoxy-bodied parts.. from the early PC cache-RAM that was just epoxy and pins, to power transistors and audio power amp modules more recently. So much for global trade. As distributors source components, they're rarely certain about the quality anymore, and possibly more concerned with only the cost difference of various sources. I think the chances of finding fake components is more likely when they're purchased from a mega-huge supplier like present-day MCM. Fakes from smaller suppliers can happen too, because the fakes seem to be getting into numerous supply chains. Everything has changed with China as a mainstream source of almost everything. Another aspect might be that there is always an abundance of surplus and transporting it globally is fairly inexpensive. So what does a guy do with 3 million excess empty TO-3 cases? Scrap value might not be very much. I don't recall hearing of fake components being found in ECG/NTE packaging. As I'm sure you know, the cost difference isn't because of the individual packaging in the plastic bag. I've purchased some hardware parts (coaxial power connectors) from some China sellers on eBay recently, and the poor quality is surprising. The difference in quality is far below that of (RS) that shack store, who's parts aren't anywhere near high quality (but some of their products are from Taiwan, not China). Chinese manufacturers can produce decent quality parts, but they don't need to when their parts are found in supply chains (not that I'm saying that eBay is a supply chain for reliable parts). -- Cheers, WB .............. "Mark Zacharias" wrote in message ... First, thanks to Chuck Hart for mailing me the schematics. OK, well, there's this bi-amped powered loudspeaker. The tweeter amp is blown. The outputs are 2N6284 and 2N6287 Darlington TO-3 package transistors. Pretty obscure these days. The schematic info also included NTE subs but those were nearly 20.00 each, with no guarantee in my mind as to quality, etc. So I ordered the 2N numbers from MCM. More like 5.00 each and I've had pretty good luck with MCM lately. When I received them, they were mismatched vendor markings, and one looked like cheap crap so I tested them right away. Actually, the one that looked like crap was OK, but the "2N6287" with Thomson ST markings was SHORTED emitter-base right out of the chute. I called MCM - "Oh, gee we're sorry" and they sent me another, no need to return the bad one. So I cut it open. It wasn't even a Darlington, just a single emitter base junction and the die was only 2mm instead of 5mm. There was a visible gash across the die, so obviously the thing was never tested in manufacture. So I receive the replacement. I test it, and this one is OPEN emitter base. Once again I call MCM, got credit and no need to return them, so I cut this one open as well. Here's the fun part: The transistor case was EMPTY. No die, no leads, just an empty case. I've emailed pics to MCM. With a little more research I was able to get the Onsemi MJ versions from Allied, so all is well, and the repair worked out OK. Those on the group using a binary server should see the pics. Anyone else interested, I can email them to you. Mark Z. |
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