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PostPosted: 02 Dec 2014, 01:32 
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Joined: 19 Nov 2014, 14:35
Posts: 2
This is just an FYI:

Back in May 2014 I ordered 100 UA741CN general purpose Op-Amps from eBay and ended up having to re-order using a different general purpose Op-Amp number from Digikey because the original eBay order Op-Amps did not work.

At first I thought it was the particular flavor of Op-Amp that my design was sensitive to. Just a few weeks ago I tried to re-incorporate the eBay Op-Amps into another project to see if I could salvage the order from May.

I was still scratching my head, even with a simple comparator circuit I bread boarded just to test. I was not even getting basic functionality. I noticed when I touched the scope probe which was supposed to be a driven output from the Op-Amp that it appeared to act like a floating input. This led me to test the other pins of the Op-Amp ... pin 8 showed a logic HIGH when it was supposed to be a NC, pin 1 however showed the "correct" or expected Op-Amp output. After further R&D the supposedly single Op-Amp was indeed a mispackaged (<- laser markings) DUAL Op-Amp.

So the pinout is:

1 - Output_A
2 - INVInput_A
3 - NonINVInput_A
4 - Supply -
5 - NonINVInput_B
6 - INVInput_B
7 - Output_B
8 - Supply +

ALL One hundred of the UA741CN's were like this. I contacted the eBay seller urging him to take a random sample from his stock, but have not heard anything from him.


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PostPosted: 02 Dec 2014, 19:35 
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Joined: 06 Apr 2009, 10:08
Posts: 1732
Location: US Pacific Northwest
Congratulations, you have had your first experience with counterfeit parts. :bawling:

The probability of getting a counterfeit part greatly increases based on the design age of the part. The design age is the elapsed time from the first availability of the part to the present. The design of the 741 op amp is ancient in technological terms. In fact, I know of no current producers for a 741 op amp. The nature of op amps is that there are MANY current production parts which will function just as well, if not much better, in any design you can conceive.

My very strong recommendation is to never buy ANY integrated circuit from someplace like eBay. With so many good reliable suppliers of production parts (DigiKey, Allied Electronics, Arrow, Newark, Mouser, etc.) there is really no reason to go elsewhere. What you save will likely be a false economy at best; as you have learned.

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PostPosted: 03 Dec 2014, 00:32 
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Joined: 19 Nov 2014, 14:35
Posts: 2
Thanks Suncalc ... I don't think these are counterfeit, as they would probably have worked even if they were counterfeits. I think these were just marked incorrectly as a result of human error at the foundry. They are definitely a DUAL Op-Amp in a single Op-Amp package label.

"With so many good reliable suppliers of production parts (DigiKey, Allied Electronics, Arrow, Newark, Mouser, etc.) there is really no reason to go elsewhere." - Agreed, however there are some exceptions and I wouldn't make a blanket statement to rule out ALL eBay sales for IC's.


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PostPosted: 03 Dec 2014, 01:00 
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Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
They may not be "fakes" per-se, but factory rejects. A lot of chips, LED's, etc. destined for the rubbish end up out the back door and even reputable Ebay sellers get had the odd time on their re-supply.

Cheers!

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* Ratings are for transistors - tubes have guidelines*
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PostPosted: 04 Dec 2014, 20:28 
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Joined: 04 Jun 2008, 20:59
Posts: 4324
Location: Arizona, USA
I suspect that they were a different type that was electrically similar, but repackaged in a different configuration for a special application. A sort of house special application. Regardless I get my OPs from normal parts source companies.

Good listening
Bruce

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PostPosted: 05 Dec 2014, 11:26 
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Joined: 04 Nov 2013, 21:18
Posts: 95
Location: Florida
I ordered two OPA627 ICs from Mouser at $24 each, saw some on ebay for $8 each...yeah right.

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PostPosted: 10 Dec 2014, 18:39 
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Joined: 31 Dec 2008, 15:34
Posts: 441
Lately i've got some 2SK1058 with wrong pinout ...and they are not sensitive at all ( i wonder what kind of transistor hiding behind the shield ...it's not a 2SK1058 ). The most surprising about it all, when i was complaining to the seller "hkutsource", they wanted me to change the written negative feedback, i had given the product on Ebay. Offcourse i refused to do that !


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