Fake Ram: Identifying A Counterfeit Chip

[Robert Baruch‏] had something strange on his hands. He had carefully decapped 74LS189 16×4 static RAM, only to find that it wasn’t a RAM at all. The silicon die inside the plastic package even had analog elements, which is not what one would expect to find in an SRAM. But what was it? A quick tweet brought in the cavalry, in the form of chip analysis expert [Ken Shirriff].

[Ken] immediately realized the part [Robert] had uncovered wasn’t a 74 series chip at all. The power and ground pins were in the wrong places. Even the transistors were small CMOS devices, where a 74 series part would use larger bipolar transistors. The most glaring difference between the mystery device and a real LS819 was the analog elements. The mystery chip had a resistor network, arranged as an R-2R ladder. This configuration is often used as a simple Digital to Analog Converter (DAC).

Further analysis of the part revealed that the DAC was driven by a mask ROM that was itself indexed using a linear feedback shift register. [Ken] used all this information to plot out the analog signal the chip would generate. It turned out to be a rather sorry looking sine wave.

The mystery part didn’t look like any function generator or audio chip of the era. [Ken] had to think about what sort of commodity part would use lookup tables to generate an audio waveform. The answer was as close as his telephone — a DTMF “touch tone” generator, specifically a knockoff of a Mostek MK5085.

Most investigators would have stopped there. Not [Ken] though. He delved into the construction and function of the DTMF generator. You can find the full analysis on his site. This isn’t [Ken’s] first rodeo with decapped chips. He’s previously examined the Intel 8008 and presented a talk on silicon reverse engineering at the 2016 Hackaday Superconference. [Robert] has also shown us how to pop the top of classic ceramic integrated circuits.


26 thoughts on “Fake Ram: Identifying A Counterfeit Chip

  1. These days it is all about the QC:
    1. A test jig with a small 3.3v/5v current regulated supply (<100mA), and a labeled meter/scope banana/sma plug IO break out.
    2. A golden-standard reference silicon lot sample clearly labeled when tested in a documented circuit
    3. don't release escrow funds until tested
    4. Expose people's BS in the customer feedback area or a public forum

    The corruption of official supply chains is frustrating, and extremely dangerous at times.
    Even Digi-key ships bad lots once in awhile… some super-cap brands are a terrible 40% precision.

    I am actually thankful most chip makers have their own factory direct on-line stores now.

    1. I remember when they didn’t use to talk to you unless you bought their product by the truckload. Be funny if counterfeiting was the one that made them change their mind, just like piracy changed the music industry.

  2. someone had relabeled the DTMF die as a Texas Instruments 74LS189 chip

    or maybe it was done that way to smuggle the part to a country that should not have it.

    for example there is an export restriction on a spark gap trigger (https://www.armscontrol.org/print/3732)

    so disguise the part as a spark gap surge protector or a quench tube or even neon lamp (if it gives off any light) and get it past arms inspectors.

    1. Wow, the risks of dual-use items being exported.
      Bottled water has legitimate medical uses for rehydration, but can be used for water boarding.
      Wood can be used in the energy industry for power generation, but in the hands of a terrorist can be sharpened and poked through a soldier.

      1. Even as a non-American you get to deal with this. If you buy accelerometer parts from Ebay, shipped from China to a country that’s not the US, with the part probably never even coming close to US territory, you still have to pinky promise not to import the part to any country on the naughty list.

        1. I once ordered a sample from Maxim via their website. I had to tick a list of things I won’t do with their part I won’t use id to make a biological or chemical warfare weapon or use it in production of such weapons, I won’t make guided missiles, anything nuclear, including but not limited to military-grade plutonium, nuclear warheads dirty bombs, etc. Nest page I had to confirm that I’m not from Iran or North Korea. Because “Poland” in address field wasn’t good enough…

          1. You can live in Poland, but be Iranian. Just as you can be an Iranian in the UK for some considerable period of time and then be mistreated by a US company when they take over your employer…

        1. What I don’t get is… why put a die in at all?

          I’m not a chip engineer, but from my little knowledge, they could save the chip (that’s near zero, I assume), the placement and the bonding (what do those cost: a fraction of a cent?)

          I’d be really curious.

          1. Easy — simply supply and demand; the cheapest parts are going to be the ones that nobody needs that there are the most of. And that means surplus.

            There are companies that sell dummy SMT components for pick-and-place throughput testing, like http://www.topline.tv/, However because their quantities are low, they end up being much more expensive than random surplus parts of the same size and form factor.

        2. It has even it’s power pins on different. So it’ would not pass the most basic tests of an ICT (substrate diodes). For me it does not qualify as a fake, but I think there must be another reason for it’s existence, like disguising a functionality of a product or discourage the copying of the product.

  3. Once worked for a now defunct defense contractor. On a military project they needed a hard to get integrated circuit. One of the buyers (later fired for accepting ‘gifts’) asked the program engineer if there was a real need to have the integrated circuits to be labeled with the part number, manufacturer and date of manufacturing. The program engineer blew up and tossed the guy out of his office. About a year later the company fired everyone of the purchasing agents. They took their ‘gifts’ with them (a television, set of four tires, etc). This was all in the late 70’s to early 80’s.

    We also got caught in the counterfeit mechanical hardware scam. CEO saw the expose on 60 Minutes, called up the buyer and asked if we were using any of the people discussed on the program to supply hardware. We were. Next day all of our hardware was tossed in the dumpster. Hard pressed to get any screws, nuts, washers as it was taken out of open stock and put into the stockroom.

    1. Had a conversation with a Martin-Marietta purchasing manager about how we should be able to get him a cheap refrigerator seeing as we were in the electronics business and wanted him to sign a maintenance contract.

  4. I’m thinking they screwed up and put wrong marking on it. I mean – if you want to make money on cloning mk5085 you have to sell it as mk5085, not as 74LS189. Anyone who receive the 74LS189 would just declare it DOA and request a refund and if that’s the goal why even spend the money on installing a chip at all?

    1. Probably because, in some twisted sense, it’s better to actually have ‘something’ in there. If the buyer got around to complaining they could offer up some vague excuses. But if the chip package was found to be EMPTY they’d be hard-pressed to defend that.

  5. China very likely – ugh… Where I live (S.E. Asia currently) China, India, and even Pakistan sourced fake prescription drugs are common, many of which are live-sustaining. Even otherwise reputable and licensed local pharmacies are struggling with this. The Government tries their best to police this, but ultimately the problem is too big and discovery (which is difficult) comes far too late for the victims who not only waste their money – their health suffers as a result.

  6. I need to generate a stable sine wave to build a synchro control transformer emulator. I was gonna use a Max038 as a function gen, but I’ve avoided buying one, because I suspect EVERY ONE OF THEM I SEE on ebay, and they don’t even make the chip anymore… I just imagine endless piles of blacktopped chips from China, resold as Max038s… It’s paranoia, but it feels justified. I’m tempted to try something discrete. It’s a one off project.

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