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TL494CN vs Tl494IN, possible EBAY fakes

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Mosaic

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Recently I purchased some cheap 'CNs' off ebay....got mixed in an "IN' application I had designed that did not require IN spec. but I had INs on hand (from Newark) so I used em.

Cost me 34 hours of trouble shooting a complex 3 PCB circuit that finally points to faulty drive transistors in the CN version.
I replaced the TL494CN with another TL494CN as a first step ( first 5 minutes of debug) to isolate that part....then went on to debug everything else (which involved shotgun changing 3 other ICs, blowing up a 28pin microcontroller due to a slipped scope probe, and lots of hair pulling and cussing.

Eventually found it by using freeze spray on the replaced TL494CN. Cold = works, room temp = stuttering.

The CNs which MUST be FAKE demonstrate an inability to drive a 4n35 opto (1.3V LED) via a 270Ω dropping resistor (with a 5Vc supply, common emitter config) without going wonky. Basically stuttering at anything past around a 10mA draw from the driver (supposed to be 2oomA spec). They drive a 1.8V red LED with the 270 Ω just fine, which happened to be my test jig...so damn misleading.

I'll just dump the lot of 'em... notably the EBAY versions of the CN have a much larger font silk screen print than original TI parts....too tired to swap in OEM TI CNs to evaluate..just need to move on now.

Maybe I'll do a follow up test on OEM CNs later on.
 

kubeek

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Just makes me wonder why you´d want to go through all of that? I never bought a single electronic part through ebay (not counting assembled modules and other junk), and I plan to keep it that way.
 

chemelec

Well-Known Member
China Parts I Assume?
If they don't work Properly, I would ask for a REFUND.
 

audioguru

Well-Known Member
Most Helpful Member
Genuine electronic parts are inexpensive and are available locally. Then why buy cheap Chinese fakes from ebay?
 

JonSea

Well-Known Member
Most Helpful Member
Just makes me wonder why you´d want to go through all of that? I never bought a single electronic part through ebay (not counting assembled modules and other junk), and I plan to keep it that way.
I have purchased many different components from ebay without any problems at all. Digikey and Mouser have had problems with counterfeit parts too so that's a pretty broad bush to slam every vendor on ebay.
 

chemelec

Well-Known Member
I haven't bought very many parts from China, but most have been OK.
I have noticed that the IRF640 Mosfets, Don't fully meet Spec.
But OK for Non-Critical applications especially to their voltage rating.

Upon sending a Complaint, I received a Full Refund, and no need to return the parts.
Most of these Vendors want Happy Customers.

Digikey wants 98 cents each for quantities up to 100 pcs, Plus Shipping Cost.
From China, one listing is 50 Pcs for $12.00 and Free Shipping.
Some others are around $22 for 50 Pcs.

Although delivery from China is usually a Month or more.
 
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kubeek

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Most Helpful Member
I have purchased many different components from ebay without any problems at all. Digikey and Mouser have had problems with counterfeit parts too so that's a pretty broad bush to slam every vendor on ebay.
I am not saying that everything on Ebay is crap, some things there are of adequate quality for the money, I meant that I just don´t see why would I buy semiconductors on ebay when I can get them along with all the other parts that I need anyway through standard supply chains, with much lower risk of the parts being fake and causing me hours of headache and wasted time.
Upon sending a Complaint, I received a Full Refund, and no need to return the parts. Most of these Vendors want Happy Customers.
A refund and no need to return might seem nice, but they don´t refund the time you spent figuring out the bad components and possibly other damage caused by them.
 

chemelec

Well-Known Member
I Tend to Breadboard one of the New parts I buy, to see if they appear OK, before using them.
Regardless of them coming from the USA or China.
And I have Never had any of these Parts to cause Damage to any other parts.

Batteries from China are a Different Story.
Even Many from Local Stores
 

tcmtech

Banned
Most Helpful Member
I used to be a big ebay buyer and I can't say I have ever had any major problems with bad components from china or anywhere else either and the few questionable ones I did get were given full refunds and or new replacements that did work as they should have.

Grossly overrated sub C NiCd and NiMh cells (100% US based sellers every time no less.:mad:) were the only real memorable questionable items I ever got and ever then I got full refunds and or good cells sent to me to make up for the bad ones.

Bad buyers and ebays increasing unwillingness to give any support to sellers being scammed by bad buyers (100% US based buyers as well) was the killing point for me ever using them again. :mad:
 
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