Toronto, Ontario, Canada

Beware fake parts

2021-01-21

There are a lot of counterfeit electronic parts in circulation. It's especially a problem with parts that are obsolete, hard to find, or expensive; sold privately in places like eBay or AliExpress at unusually low prices; and shipped from the People's Republic of China. However, just this week I had to deal with a batch of fake TL074 op amps from a well-known US distributor. Here are some notes that might help others avoid, or at least debug, similar problems.

The TL074 is a very popular quad JFET-input op amp chip, used in many synthesizer circuits. I use this type in the Leapfrog VCF, Fixed Sine Bank, and Middle Path VCO (and the closely-related TL074B in a few other products); basically everywhere I need an audio op amp. Although this is a good-quality chip when it's genuine, it's not a particularly expensive chip. It might retail for US$0.35. It's still in production, available from more than one major manufacturer, and not normally in short supply. One wouldn't think the TL074 would be a big target for counterfeiting.

The conventional wisdom is that counterfeiters will go for stuff like the out-of-production µA726, which is used in a lot of classic synthesizer circuits, has no good modern replacement, and might be worth over US$100 to a hobbyist today if genuine. That kind of target provides a lot of margin to cover faking the packaging, putting some kind of chip in the package that will fool the simplest acceptance tests, and so on. "Black-topped" chips are notorious: a cheaper chip, or even an empty DIP package with no chip inside, may have its markings on top covered by textured black paint and then new markings applied to make it look like a more expensive chip. Another dishonest practice sometimes observed is to sell chips that are really the type they're claimed to be, but are used (possibly non-functional) chips pulled out of old equipment and dressed up to look new; and it's hard to imagine a chip that sells for US$0.35 being worth that effort.

So I wouldn't normally think I needed to be as cautious about TL074 op amps as I might be with, say, AD633 analog multipliers (much more expensive and rare). Ken Shirriff did some reverse engineering on a counterfeit AD633 recently. But there has been a supply crunch on TL074 chips recently. Very likely the global pandemic is at least part of the cause. I recently ran out, and my usual suppliers were all out of stock. I've heard from other people also having trouble sourcing them. For a while it seemed like there just were no TL074 chips to be had; and I needed some more to continue producing my own products. So I went looking at alternate suppliers, distributors who wouldn't normally be my first choice. RS Components said they had this item, and I tried to place an order there, but they rejected my credit card, so after a couple of tries I decided to keep looking. I eventually went to Jameco - even though I had misgivings about dealing with them.

Jameco Electronics is a popular distributor of parts to hobbyists, based in California. Almost 30 years ago, in the early 1990s when I was a teenager, I had very little money to spend, and the Net wasn't a thing available to the general public, Jameco sold me a shoddy drill press that I couldn't use and couldn't get refunded or replaced. I decided I didn't want to go back to them again. But now in 2021, they seemed to have the chips I was looking for, nobody else did, and I figured, okay, maybe they deserve another chance. After all, it's been a very long time. The point I'd like to make is that although I had a personal reason to avoid Jameco, and they're certainly a lower tier than Mouser or Digi-Key, Jameco is not some fly-by-night deep-discount seller on eBay or AliExpress. Hobbyists have been using and trusting Jameco for many years and they're not an outfit one would normally expect to catch selling counterfeit parts.

There were a couple of warning signs early on. For one thing, although I paid extra for a higher-tier UPS shipping service that I thought would include Customs brokerage service at no additional charge, I still ended up having to pay an additional charge for brokerage, talk to UPS customer service on the phone, and wait an extra day for the delivery. I've got an account set up with UPS so that brokerage charges will be automatically charged to my account, and that has worked fine for other packages; but for some reason (and I will probably never know why) it didn't happen on this one package, this one package had to be paid manually, and there shouldn't have been a brokerage charge on this package anyway. The point being: delivery of the package was irregular, not what I expected and not like other packages. But all that could easily have been UPS's fault, not Jameco's, and it shouldn't necessarily bear on the genuine/counterfeit status of the chips inside the package.

I unboxed the package live on my Twitch stream and noted another irregularity: the chips were packaged just in their anti-static rails rubber-banded together. The rails weren't in a shield bag. I don't think I've ever seen a major distributor ship DIP ICs without a shield bag before. I myself have a big enough pile of those bags sitting here that getting rid of them is a bit of a waste disposal issue. So, fine, I can put the rails in a bag of my own, that's not a big problem. Maybe that's just how Jameco does things. And these chips are not particularly static-sensitive anyway, and they were in anti-static rails which should be good enough to protect them. Not a big problem. But: it was another irregularity.

I later noticed that the anti-static rails on the genuine TL074 chips I still had on hand from another distributor, were printed with the words "TEXAS INSTRUMENTS STATIC DISSIPATIVE," and some numbers and recycling information, while the rails on the chips in the batch from Jameco had no printing. But that's also not particularly damning. Texas Instruments probably has many variations on the details of the anti-static rails they use, and chips bought from a distributor might be repackaged from the way they came from the factory, without anything untoward having occurred.

However, when I took the chips out of the rails to examine them, the red flags started going up. Here's a photo of one of the chips I got from Jameco last week (bottom) compared to a believed-genuine chip I got from Mouser in October 2020 (top).

image of real and fake TL074 chips, top

Several differences are obvious between the two chips but most of those differences could be innocuous. The chips are slightly different shades of grey. The notch at the end (indicating pin 1) is a different size and shape. There is a round indentation on the lower chip, also indicating pin 1, but not on the upper. Both sets of pin 1 markings are within specification and I've seen those kinds of markings on genuine chips; as far as those points go it could be that the two chips were made in different factories with different moulds. TI has many different factories. The typeface is different in the etched markings (wider on the lower chip) but that could also be a factory-to-factory variation.

There are differences in the leads and plating: the upper chip has narrower leads with slightly oxidized, once shiny, tin plating. The lower chip has brighter, unoxidized, matte tin plating. The oxidation difference could simply be because my older chip is older. I haven't been able to find decoding information for the date and lot codes in the first line of the chip markings, which would allow me to figure out how old each chip is (or claims to be, in the case of the fake one).

The mould indentations (circular features toward the right end of the chips in the photo) are different but neither of them looks suspicious. It's considered a dead giveaway of blacktopping if a package is textured inside those indentations, because the normal manufacturing process makes most of the surface textured but the mould indentations smooth, whereas the paint-like blacktopping material will leave the entire surface textured including the mould indentations. But both chips are smooth inside the mould indentations: no indication of blacktopping. Similarly, on the bottoms of the chips, one has one and the other has two mould indentations, but the mould indentations themselves look fine - smooth surface and although these doesn't show up well in my photo, they both have crisp text markings inside the mould indentations, which is another thing counterfeiters sometimes get wrong.

image of real and fake TL074 chips, bottom

I tried wiping both chips with acetone, because that's another popular test for blacktopped chips. Real ones are supposed to be made of plastic that resists acetone, and marked by laser etching. When you wipe the acetone over the surface, the markings briefly disappear (as the liquid fills in the roughness created by the laser) and then seem to "pop" back into existence as it dries. If the surface or the markings smear away (because they're paint, dissolved by the acetone) that's an indicator of blacktopping. But both chips passed that test.

The biggest warning sign on visual examination had to do with the Texas Instruments logo in the upper-line marking. On the real chip from Mouser it's a fairly accurate representation of the map outline of the state of Texas, filled in, with a readable letter "i" superimposed, and the entire logo is about the same height as the text. On the fake chip, the logo is taller, and crudely formed: bigger rectangular notch at the West, no sharp point at the South, the letter "i" is only approximated, and there are squiggles around it. Texas Instruments has used a number of different variations of their logo, and there is a not-filled-in version they've used on some chips which looks a little like this one. But the one on the chip looks more like it's "Tianjin Instruments." Somebody unfamiliar with the map of Texas probably drew it with a joystick on an industrial laser-etching machine somewhere and called it close enough.

I have since found a report from user ChristianBloch on the Look Mum No Computer Web forum, who seems to have gotten fake TL074 chips on AliExpress that visually resemble the ones I got from Jameco.

I tried putting the suspect chip into one of my Middle Path VCOs as U2 (triangle buffer and sawtooth and pulse shaper for channel A) and tried the different features, with the frequency set to a few hundred Hertz. At first I thought it was working - all the outputs coming from that chip looked the right shape on the oscilloscope screen. That suggested the suspect chip was at least a quad op amp of some sort, doing the things in the circuit that an op amp should do, and I almost decided "I'm being silly, this chip is fine, a reputable distributor wouldn't be selling fake ones" and dropped the whole thing. But, I decided to run a few more tests.

I tried using a multimeter's "diode test" in both directions between each pair of pins on each chip and here's a photo of my handwritten notes from that. This is the kind of test sometimes used for identifying an unknown chip.

diode-test on the pins of the chips

The point here was to infer the nature of the circuits inside the chips; and the important result for me wasn't the specific voltages but the fact that the pattern is different. The set of measurements on the left (from the old batch of chips) shows a forward voltage from every op amp output and each of the two power pins, to all other pins. That might well result from protection diodes built into the circuit, and the kinds of stray diode junctions we expect to see in a classically designed analog chip. The set of measurements for the suspect chip on the right shows some of the symmetries we might expect of a quad op amp chip (in particular, note how the pin 1 and pin 14 columns are basically the reverse of each other) but there are a lot more pin pairs with no forward voltage, and it's clear that the two chips contain different circuits with diode junctions in different places. So this is building up the picture that it's a quad op amp chip but it's not a TL074.

I put the suspect chip in the Middle Path again, turned up the frequency, and scoped the pulse output, and here's the result. As I said on Twitter, it's a smoking gun.

waveforms from good and bad op amps

Old chip at left, new at right. There's just no way the new chip can be a genuine non-defective TL074 and do that.

The left trace, from the believed-genuine chip, is a sharp square wave, even at 20kHz. The rise and fall times are under two microseconds. The right trace, from the fake chip, is rounded off and slew rate limited. Op amps normally have a "slew rate" representing the maximum speed at which they can pump their output voltage up or down. On large step signals they usually work by switching a fixed current around to charge an internal capacitor up or down, which causes the voltage to go up or down in a straight line. Those straight-line slopes on the voltage are pretty much classic op amp behaviour. The problem is the steepness of the slopes: the fake chip's slopes are much less steep than those of the real TL074.

The test circuit used for those scope shots isn't ideal. I just plugged the chips into my MSK 013 prototype and scoped the output because that was convenient, but in fact that circuit is using the op amps as comparators (on the one hand: we're traditionally told not to do that; on the other hand: it works), and the output I'm measuring is not the direct output from the chip but the module output downstream of a Zener-diode clipper. So in this circuit the op amps are being pushed pretty hard both for switching time and output current, and I think that's why we see effects like the rounding at the top of the pulse in the right-hand trace. Very likely that chip, whatever it is, isn't able to drive as much current as the TL074 would, so as the clipper starts to kick in, it can't drive the voltage up much further and the pulses get rounded. I think the comparator application and Zener clipper are also the reason that if you do the math from the voltages and times measured by my scope, it appears that even the genuine TL074 is not hitting its full specified slew rate here.

But even with those caveats this measurement makes it quite clear that the chips in the batch from Jameco were not genuine, normally-functioning, Texas Instruments TL074 op amps. I sent my photos and scope shots to Jameco customer service and although they didn't directly acknowledge that the chips were fake, they agreed to give me a refund under their guarantee.

Before packing up the chips to send back, I did a live stream in which I tested them a little more thoroughly for slew rate, in a more proper slew-rate testing circuit; and I screwed up by using the wrong format of USB key saving the screen shots and I ended up losing all the measurement results. Between that and the mistakes I made along the way while trying to do the measurements on-stream I ended up with very little to show for the effort, and it's kind of embarrassing and I'm not sure I want to link to it directly, but at least for the duration of Twitch's archiving you'll be able to find it on the "previous streams" page of my Twitch channel.

Please note that I no longer have the fake chips. As of this writing they are en route back to California, and I cannot do further tests, send samples to people who want to decap them, etc. I will delete comments from readers who fail to understand this point.

Mouser claims to have gotten TL074 chips back in stock as of yesterday. They haven't shipped my backordered batch yet, but I hope they will today. I'm out of pocket for the brokerage fee and the shipping of the bad ones back to Jameco, but they say they will refund the original payment I made to them for the chips and shipping to me, and assuming they do that, I end up not really losing much. And it may be another 30 years before I order from Jameco again.

It's a good thing I was cautious enough about chips from a non-preferred supplier to take a close look at them and run the tests, because it would've been bad if I had shipped those fakes to my own customers in kits or assembled modules. This goes to show part of the value of buying a full SDIY kit from me instead of trying to do your own sourcing with the "PCB and panel" products available from some other SDIY vendors. With a full kit, you know I've already done the sourcing work and I've made some effort to be sure the parts are genuine.

The take-aways for hobbyists are that even a popular distributor may be selling counterfeit parts; even inexpensive easy-to-find parts may sometimes be targets of counterfeiting; and counterfeiting may go all the way back to the original factory (brand-new chips that really perform the right general function, falsely labelled right from the start) instead of classic blacktopping or used chips sold as new.

Listening longer to the Mandelbrot Set || Passive multiples and friends

Comments

Can you expand on this some more? I have some TL074 chips that I got from UT Source which thankfully I haven't put in any circuits yet. The TI label and font look genuine but they also have the same physical aspects as your fakes (smaller notch, dimple next to pin 1, and only 1 mold circle on the rear).

What tests (and how) could I do with a multimeter and o-scope to figure out if they're real?

I'm an electronics dummy who is trying to learn, so I apologize if the answer seems obvious.
Armand - 2021-01-21
The big issue seems to be that the bad ones are slow; their slew rate is too low. See the two oscilloscope screenshots in my article above. The good chip can produce a sharp-edged square wave at about 20kHz and the bad chip can't.

Probably the simplest reliable test would be to test the slew rate using one of the op amps as a comparator. That'll call for an oscilloscope, power supply, and some kind of signal generator or oscillator that can produce a waveform of a few volts around zero, ideally at about 20kHz though a lower audio frequency would be okay. Hook the chip up to power (+12V to pin 4, -12V to pin 11; needn't be exactly those voltages but the power voltages should be within range for the chip, so anywhere from +-5V to +-15V should be okay); hook a negative input like pin 2 to 0V; hook your signal generator to the other input of the unit (pin 3); and use the oscilloscope to view the waveform coming out the output (pin 1). In that configuration the op amp should be comparing the input waveform against zero and driving the output high when it's above, low when below. A good chip should take only a couple of microseconds to swing from one power rail to the other, whereas a bad one might take much longer. If you have a known good chip to compare against, that's quite useful; the difference from a good one to a bad one is pretty dramatic.

I attempted a more elaborate slew rate test in my most recent live stream; it didn't really go very well but you could go watch that to see what I was doing. https://twitch.tv/matthewskala/

Another way of testing them might be to replicate what I did with the diode-test range on the multimeter: measure from each pin to each other pin and make a chart like the ones shown in my photos. The good chip showed a forward voltage from each output and negative power (pins 1, 7, 8, 11, and 14) to *all* other pins, and from pin 4 to most other pins. The bad chip had a more complicated pattern with fewer forward voltages.

Of course, that's describing how one might detect a chip that is bad *in the same way as the ones I was looking at*. It's entirely possible that a bad chip could be bad in some other way. But I think the low slew rate issue is a pretty common way for fake op amp chips to be bad.
Matthew Skala - 2021-01-21
Great write-up as always, Matthew, but I take a bit of issue with something you said:

"This goes to show part of the value of buying a full SDIY kit from me instead of trying to do your own sourcing with the "PCB and panel" products available from some other SDIY vendors."

I've seen you write before that kits and assembled modules are the backbone of your business (margins are much better). And that makes 100% sense and I don't fault you for taking this opportunity to advertise your kits.

Where I take issue is the part that could be construed as a knock on vendors who only sell PCBs and panels. Not everybody trying to make a few side bucks in the SDIY game has time to organize and assemble full kits to sell. I don't think that should preclude them from business. I know you probably didn't mean to imply this but it doesn't hurt to be careful with one's language.
Ben Reeves - 2021-01-27
Thanks Matthew, I think I can follow those instructions.
Armand - 2021-01-27
Ben: let's bear in mind that we are not having this discussion in a community forum like Muffwiggler, but on the Web site of my commercial business. It's nice if people drop in and read the articles I post and get something useful from that and leave, but I am not writing here just for fun or just as a public service. I'm trying to attract customers to buy my products. I shouldn't lie or mislead, but I think it's okay for me to explain truthfully why I think my products are better than the products offered by other vendors. And I'm not obligated to give the other side of each question equal time.

Anybody running a business in competition with mine should have thick enough skin to deal with my saying that I think my own products are better and saying why, and goodness knows some of my competitors are much harsher toward my products and business practices than anything I've written above - and much more eager to point at me personally (directly or through shady insinuations) instead of talking neutrally about categories of products.

Now, I didn't say that anyone should be *precluded* from selling products different from mine; only that I think the kind of product I sell is better than a different category of products I don't sell. I do think it's an interesting question - and I discussed this in one of my recent live streams - why PCB and panel is popular among vendors when it doesn't seem to make business sense for me personally. I think it has to do with scale. PCB and panel has a better margin, meaning that the vendor can keep a larger percentage of the retail price as profit. So a large outfit looking to make as much money as possible for a given amount invested, and not tied to making that money from a few specific module designs, will find that attractive. It's probably also attractive to the small vendor, maybe someone who's a hobbyist not using this as their main income, who as you say doesn't have time to organize full kits and maybe is just hoping to defray the costs of their own hobby. The person in that position wants to have a product others will pay for, with little or no additional dollar investment in buying parts. In either of those cases selling PCB and panel sets makes more sense. My position is unusual in that my business is in between those two sizes, at a scale where selling full kits actually makes more sense.

That's from the seller's point of view. From the buyer's point of view, I think full kits are good but it's clear from their popularity that PCB and panel sets also have advantages that matter to many buyers. It's nice that both are available and people can shop around.
Matthew Skala - 2021-01-27
Great points all around. In retrospect my comment came from an immature place of jealousy for those who have dedicated themselves to their business and managed to make a name for themselves. I'm only just getting started and don't even have a business to speak of. As someone with a steady day job who doesn't have to make my living off my (not even existent yet) business, it was very presumptuous of me to offer such a critique. Forgive me for the criticism and thank you for your contributions to the SDIY community!
Ben Reeves - 2021-02-05
Well, we don't need to take any of this too seriously. There's room for multiple ways to do things and that's part of the fun of this hobby.
Matthew Skala - 2021-02-05
I first read about fake chips about 10 years ago on the sparkfun blog. They eventually found out that the fakes were rejected ON Semiconductor parts that some one fished out of the trash and sold on to some one who relabeled them. Fake parts suck though the topic is pretty interesting. Like you, I've been buying from Jameco for a long time to and I'm disappointed that they let fake parts get through. But if even places like Sparkfun can get fooled I can't be too mad, just as long as they take the parts back and you get a refund. (And they don't keep selling the fakes).
slick8086 - 2021-02-13
"Like you, I've been buying from Jameco for a long time "

Um, did you read the article? I bought from Jameco once, almost 30 years ago; felt that I was ripped off at that time; and I made a point of *not* buying from them again until just now, when I got ripped off again. I won't give them a third chance soon.
Matthew Skala - 2021-02-13
I've had the same problem with some TL074s i bought both from Aliexpress and from a local reputable distributor. from what I've measured, these are most likely rebranded LM324s, which have a much lower slew rate. One solution one might use to not have to trash all of these (someone such as me who bought dozens of them before making sure they were genuine :P) is to work with a lot lower voltages on them (calculated to be up to 2Vpp, to have a reasonably reliable output up to 40kHz) and have a single transistor amplifier stage at the output plus a current gain buffer stage. This is not the solution to everyone, as it will not anymore be a "drop in" substitute to faulty tl074s in other circuits, and requires more components, BUT it still enables its use as a tl074 in a pinch.
Aroeira43 - 2021-03-01
Why don't you buy directly from Texas Instruments, it has a good price and the transport is cheap ...
Stromgolf - 2021-08-07
They were out of stock at the time.
Matthew Skala - 2021-08-07
Anti-spam, fill in the blank: North Coast

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