When you go on your favorite cheap online shopping platform and order a batch of 74LS logic ICs, what do you get? Most likely relabeled 74HC ICs, if the results of an AliExpress order by [More Fun Fixing It] on YouTube are anything to judge by. Despite the claims made by the somewhat suspect markings on the ICs, even the cheap component tester used immediately identified them as 74HC parts.
Why is this a problem, you might ask? Simply put, 74LS are Low-power Schottky chips using TTL logic levels, whereas 74HC are High-Speed CMOS, using CMOS logic levels. If these faked chips had used 74HCT, they would have been compatible with TTL logic levels, but with the TTL vs CMOS levels mismatch of 74HC, you are asking for trouble.
CMOS typically requires that high levels are at least 70% of Vcc, and low to be at most 30% of Vcc, whereas TTL high level is somewhere above 2.0V. 74HC also cannot drive its outputs as strongly as 74LS, which opens another can of potential issues. Meanwhile HCT can be substituted for LS, but with the same lower drive current, which may or may not be an issue.
Interestingly, when the AliExpress seller was contacted with these findings, a refund was issued practically immediately. This makes one wonder why exactly faked 74LS ICs are even being sold, when they’d most likely be stuffed into old home computers by presumably hardware enthusiasts with a modicum of skill and knowledge.
I would posit that if they’re re-labeled that might have been done when they were decamped from their original boards and warehoused. I’ve gotten the impression from some conversations that that happened some time ago when dead electronics were pouring into China. In which case the shipping seller might have no idea they’re not really what they’re labeled as.
That might not be what’s happenign but it might be more likely than someone relabeling the chip incorrectly then shipping it. Maybe someone with a closer eye on the origin of the chips can weigh in.
Ewaste imports have been banned, but plenty of smuggling via HK, still china has plenty of stock from before the ban and domestic waste plus many relabel companies, hundreds of thousands…
Yup, the instant refund seems to me more an indicator that seller has been scammed with fake chips before, frequent enough to believe the buyers claim without needing to check, and doesn’t want angry customers so did the only thing they could to “make it right”
It certainly could also be interpreted as getting caught and wanting to make that go away.
I prefer to err on the side of the pool of victims is larger than the pool of scammers, but I know not everyone agrees.
I have a drawer full of bmp280’s that were sold as bme280’s, down to the proto of the actual device. I have gone out of my way to ask up front if they are really bme280’s as it would save us both a bunch of time to end it at this stage. I get the usual the chips are as advertised and when they are not, that is another 5 free devices for simpler projects in the future.
Given that I send images of what I got, and what the real thing should look like it seems kind of hard for them to play dumb, but apparently that is what they do, and if they have to eat the occasional return, that is just part of doing business.
I wonder if these are programmable logic and are programmed and case marked according to expected function. This way only a single part needs to be fabbed which brings costs down. obviously it would then be tempting to maximize the portfolio offered.
or it could just be a fact that bipolar fab processes are less popular (speculation) than they used to be and therefore a LOT cheaper to stick with cmos.
would be neat to decap a bunch of these to see if either of these are true.
Can you still give negative feedback when you accept a refund?
If I had to choose, I’d rather give negative feedback then get a refund, the cost of these IC’s is negligible, and probably already less important then the frustration caused by the extra delay of having to re-order IC’s (and the time needed for pacing the order, emptying your letterbox, opening the packaga etc).
Yeah, you can always leave feedback, regardless of a refund. Not sure whether sellers can get feedback removed.
“74HC also cannot drive its outputs as strongly as 74LS” what ?? surely that is backwards
HC pull-up is around 60-100Ω, pull-down 30-70Ω (at 3-5V Vdd). LS pull-up is fairly weak (~100Ω), but it doesn’t have to pull as far (2V min, from ~3.5V open circuit), so could arguably be said to be stronger for its purpose. LS pull-down is quite strong (~20Ω?) and saturates towards GND (well, 0.3-0.4V I guess, thanks Schottky).
Hence why so many TTL control signals (often data too) are active-low; in addition to the use of open-collector outputs, or historical precedence from even longer ago (RTL/DTL). The leading edge is stronger, and tends to wired-OR in practice (still, not that one should be intentionally shorting TTL outputs together :) ).
I suspect they bet on most buyers not using the parts immediately and being past the refund window by the time they realise they’ve been had. That’s caught me a few times.
Without propagation delay analysis and ouput curves for switching ouputs nothing he says holds any water. But you get repainted chips from ali. I did buy these same group of 50 chips, they work. And they look repainted. I also have some relabeled 74HC181 in skinny dip. After decapping one of them, and potographing it I saw that it is indeed CMOS but as LS labeled.
He’s mainly saying CMOS are being remarked as TTL. That’s what the tester is showing, and all it needs to do is check voltage levels.
This isn’t the first time I’ve heard of counterfeit IC’s being sold online, but you gotta have your web smarts. If the deal is super good, you’re probably getting fakes or scammed. I don’t mind buying counterfeit goods, as I’m not sending anything into space.
With that, AliExpress can definitely be a little predatory in how they sell goods. Their allowed to advertise the USB cables price to an expensive peripheral, as the peripheral. You actually have to go into another menu to select the proper item at full price… So you just gotta know when they scamming foreigners or out maneuvering the foreign competition.
eBay sellers were doing the “toss in a cheap cable” to win top spot in “cheapest first” before AliExpress even existed. At least eBay includes postage. This is a easy fix, but no-one seems to be interested. (Set minimum price, exclude low price options while including the rest.)
AliExpress actually made their search worse (I know, hard to believe) by deleting some useful options. One was to sort by item prices, so for lots (eg 1000 pieces) you could sort by a single item price. Quite handy. That way back when AliExpress was Alibaba’s “little brother” selling small lots & samples, not the eBay clone they’ve turned it into.
Story after story of fake chips, transistors, ETC, ETC. When will you people learn to buy from trusted sources? OHH NO’S I bought fake fake chips again but they only cost me USD$.03 per item!!! Just buy from trusted sources and I repeat just buy from trusted sources.
Basic 74HCT00D (NAND gaet) is 0,1 EUR at Aliexpress, the same part costs 2 EUR at TME.
If I have to pay 20x normal price I can waste some time to sort bad chips because in the end I am STILL saving money to build MORE projects.
It’s the EU sellers who are scamming customers by making them pay absurd prices for chips which are made in billiards of milliards pieces every year.
yes, you’re lying.
I checked.
they cost 60 cents in singles and 13 cents in larger quantities
go away scammer
What price? https://www.tme.eu/gb/details/sn74hct00dr/gates-inverters/texas-instruments/
End all be all it’s buyer beware that’s always true . _period know your source .
I just had a recently purchased BRANDED Chinese 74LS75 go intermittent on me. I HATE intermittents. My experience has been that if 74xx’s made after the late 70’s aren’t floor sweepings, DOA, or abused, they will work for several decades.
While I feel the author’s pain about counterfeit chips, I’ve got to ask why anyone in their right mind would go to some unknown PRC supplier to buy semiconductors that they care about. Or, if this was an exercise to prove that shady PRC companies sell counterfeit parts, then I must say that I am shocked SHOCKED to find such dishonesty going on: https://www.youtube.com/watch?v=9TCZJOjnF_0&t=33s
Digikey has nearly 10,000 units in stock of the SN74LS08N, shown in the video still above, for US$0.80 quantity one. If you buy them in larger quantities, they go down to US$0.36 each.
And Digikey advertises a “Fully authorized supply chain for buyer confidence”.