Foreword
If you use reputable suppliers it’s pretty unlikely you’ll run into a problem. This is an issue I’ve only encountered when venturing into some of the less savory corners of the component supply chain in search of otherwise unavailable parts.
My particular needs are related to my building and repair of 1980s analog synthesizers so my experience in this area is related mainly to tracking down transistors and op amps used by Japanese manufacturers of that era.
In small quantities it may be safer to look to more local and reputable sources on ebay or various forums even if they’re expensive. I have opted to do things the cheap and difficult way because it seemed interesting.
Note: Stock Lies
A lot of the places I’ve encountered will say they have something in stock and might even list a very specific and official sounding quantity that they have. There is a strong chance that is a lie.
You’re most likely dealing with a middleman who is sourcing these from a number of places. It may take them a while to actually get a hold of the items and you won’t hear a peep unless you bug them for a status update. You’ve got a chance of getting partial orders shipped if you ask, otherwise don’t be surprised if you don’t hear anything for a couple months (or more).
Obvious Signs
Wrong marking type
If you’ve gotten this desparate to find a part, it’s also likely you have a bit more knowledge about it. If you’re sourcing a part that was only manufactured in the early 1980s before laser marking was a thing, that laser marked part you got is not the thing.
Shoddy markings
Old markings can look dicey in comparison to current production, but they were still done by major manufacturers. If the markings look poorly done it may be a sign to investigate more closely
Business up top, randoms below
Blacktopping (more on that later) seems to generally be limited to the top side on DIPs in a lot of cases. If you get a batch of chips with identical markings on top (same batch code especially) but a variety of markings on the bottom, they’ve been remarked and are almost definitely not what they claim to be.
More Subtle, Still Easy
Blacktopping
Blacktopping refers to spraying a new coating on a part in order to give it a fresh canvas on which to place whatever markings your counterfeiter’s heart desires. It’s intended to mimic the textured surface of a normal chip but isn’t too hard to spot when you know what to look for.
Razor test - using a sharp blade you can try scraping the surface a bit. If you start removing what looks like little shreds of black paint, that’s blacktopping. A factory chip’s textured surface is never paint.
Filled areas - ejection pin markings and underside stamps should never have the same textured surface as the rest of the chip. They are smooth plastic. The razor test applies here, but not really necessary. Counterfeiters putting in extra effort might not make this mistake but sometimes even if they tried to keep these areas clean you’ll spot errors under a microscope.
Pin overspray - going back to what I said earlier, factory chips aren’t painted. Factory chips definitely don’t have paint overspray on their legs. Easier to spot under a microscope, but sometimes visible to the naked eye too. Look at where the component legs enter the body for a spritz of black paint as a result of the blacktopping process not being masked off perfectly.
Deeper Analysis
Test your transistors
For the old esoteric stuff it may be hard to find a datasheet, but try. I’ve found that some datasheets are nowhere on the internet. My solution here has been to track down copies of old data books. Back in the old days companies made entire books of reference data for things like transistors and diodes, providing the essential data in a condensed format for a large number of parts. D.A.T.A. books are good but hard to find, Tower’s books are a little more available at used booksellers. Ebay has been more fruitful than Amazon for me but your mileage may vary. My best luck for my particular niche has been to find the Japanese transistor specific reference books, but you may also find that substitution manuals ahve the information you need. If you don’t know the years of manufacture for a part, infer it from the production dates of the equipment that used it. One issue is that the letter coding for different Hfe ranges is largely abset in the books I’ve seen, but you’re better off with something than nothing.
