|Elliott Sound Products||Counterfeit Semiconductors - 4|
Last Update - July 2018
I'm unsure why, but there seem to be people selling (and buying) these transistors, despite the fact that they appear to have been rendered obsolete around 2003 or thereabouts. Certainly, I could find no mainstream supplier listing them, but (naturally) they are all over ebay, and they aren't cheap there either. Most sellers insist they are 'genuine', but this is presumably a 'new meaning' of the word, of which I was previously unaware.
Fake 2SA1553 And 2SC4029 Transistors
The above photo was sent to me in July 2018, and the transistors were purchased from ebay. The tiny die is typical of all counterfeit power transistors. It's certainly utterly incapable of withstanding 15A or a maximum dissipation of 150W - the die is simply way too small. When subjected to even a fraction of the rated power, the die will fail. If you buy any obsolete device, it's essential to run a SOA (safe operating area) test (see Semiconductor Safe Operating Area).
In general, I cannot ... ever suggest using obsolete transistors for new builds, and for repairs you are generally better off with more modern devices. You do need to be very careful though, because there's often a good chance that an older amplifier may oscillate with new (especially higher fT) transistors. This may mean that the caps included for stability need to be changed, not something for the faint-hearted. In some cases, it may not be possible to get a stable result, which means that the power stage probably needs to be replaced with something else.
Be aware too that some 'mainstream' transistors may well be marked with their original designations, but that doesn't mean that the new part is the same as the original. This can also lead to amplifiers becoming unstable when output (or driver) transistors are replaced. It goes without saying that fake devices will never match the originals, other than the number printed on the case. Most blow up as soon as any significant load is applied.
Not what you'd expect, as this is a low-cost opamp even when purchased from major suppliers (AU$1.25 from a major UK supplier for example). At around $0.17 each from China, it looks too good to be true, and that is indeed the case. The fake device was unstable, and oscillated regardless of the presence (or otherwise) of bypass capacitors. Even the slightest capacitance at the output caused oscillation, which can happen with any opamp, but when the 'real thing' was installed the problem went away. You can see in the photo that the TI logo is not right, and the other printing is nothing like it should be.
Fake TL072 Opamp (Left), Genuine (Right)
The 'fake' device is shown on the left, with the 'fake' on the left. It's probable that the poorly marked and misbehaving TL072 is actually a 'factory reject', destined for disposal, but 'rescued' and sold on by an unscrupulous employee perhaps. These were purchased on ebay (predictably), and while they may have been only a few cents each, they are obviously just a waste of money. It might be possible to use them in something, but they will be unpredictable and aren't fit for use.
Thanks to Daniel G. for the info and photograph.
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