LM1875 how to identify fake

The LM1875 is one of the most popular UMZCH microprocessors of not high power, with bipolar power supply. The main competitors of this chip are the TDA2030A and TDA2050, but according to the experience of radio amateurs dealing with all three chips, the LM1875 outperforms competitors in all parameters: power, reliability and sound quality. Taking into account the fact that all 3 chips are interchangeable and widely used both in factory designs of different price categories and in amateur home appliances, this chip is very popular on the market and has a steady demand. Well, as we already know, demand generates a supply, and this offer is not always qualitative, but in this particular case, the offer is 95% not qualitative for all 3 microcircuits, but this is about the LM1875.

To start a photo of several instances of the LM1875 for familiarization, reflection and knowledge testing, if any. Only with us, in the store kit-amp.com, we will tell you how to identify with a 100% accuracy counterfeit. Immediately I will say that the D1875 type chips and the rest, similar to the combination of numbers "1875", will not be considered here because of lack of technical documentation for these products, which means that no one has ever officially manufactured them, and hence the conclusion is to investigate them there is no point.

Perhaps the first and most important thing to do to determine the authenticity of a product - you need to refer to the accompanying, technical documentation from the manufacturer (Datasheet). And although getting information from Datasheet does not guarantee 100% identification of a fake or original, it still helps in most cases. The manufacturer of the original LM1875 was National Semiconductor, which in 2011, bought another Texas company Texas Instruments, but the author until 2019. inclusive, did not meet the LM1875 with the Texas Instruments logo, respectively, the Datasheet is viewed from National Semiconductor. The most important thing for us is the drawing of the product, since It is through it that you can visually identify the fake. When studying the drawing, one should pay attention to everything and to any small details. Also, caliper will not be superfluous.

And so, we see: a rectangular case, without any dents on the sides with a key in the form of a recess in the lower left corner, in which you can see the letters, numbers, or combinations thereof. Above, in the direction from the substrate to the face, there is a bevel. Also, from below there are bevels at the front and rear of the microcircuit and they converge on the line of the chip legs.

In fact, this information is enough to determine the vast majority of fakes, however, the photo has a rare fake corresponding to the drawing from the Datasheet. And yet there is a unique feature of this chip, which allows, in combination with Datasheet, to 100% determine the authenticity of the product and this is its substrate. The substrate of this chip is special for this group and, despite significant differences depending on the date of production, is unique. Having carefully considered the substrate, you can see the rectangle with the admission from above at NO angle, and the older the concrete copy (large font marking), the closer to the right angle is given for the law. In some cases, the jumper from above is almost 90 ° and the corners appear only slightly rounded, but in this case, the sides of the rectangle are not parallel and have a slight convergence on the top (pyramidal). It is also worth noting that the large font is encountered in very old copies, which are not produced at present and are very rarely encountered today. In modern chips, a small font in the upper part of the body is engraved with laser engraving and is often poorly read, a substrate of the same type - a rectangle with an adhesion of about 45 °. It is worth noting that there is one exception: the LM1875L microchip from the Taiwanese company "UTC". This chip has its own Datasheet, but there is no detailed drawing there. The enclosure of this chip corresponds to the drawing in the original Datasheet, except for the key in the lower left part, which is missing. The main difference is the substrate: a rectangle that has a jumble above 90 ° and the corners are the right straight lines. Very scrupulous comparison of the sound quality of this microcircuit with the original, did not reveal any difference, respectively LM1875 from "UTC", you can rightly consider the original. Obviously UTC purchases crystals at TI and disperses them in their production.

As you have already guessed, far from all the chips on the photo are the original quality product. Part of them is an outright fake. Experienced eyes and having studied written above, determined that fake - this is a series from below, and the original - a row from above.

The author is not a supporter of defining authenticity by destroying the product, but a few weeks before writing this article, for the first time, out of about 200, he got a new LM1875 chip with a factory defect. Well, since it's not a pity to destroy the forgery, it was decided to study the inside of the original chips of the old, new and UTC samples, as well as forgery:

Unfortunately, in one case, it is not possible to consider the crystal, since it is broken off from the substrate with the plastic case, nevertheless on the substrate and on the body, it is possible to determine the size of the crystal with great accuracy, and this is quite enough to enumerate the product into the group of the original or forgery And so we see 6 chips in a row with a left to right:

1. The original of the new sample

2. Original of the old sample

3. Chip UTC, original crystal

4. Fake with the case corresponding to the Datasheet

5. Fake with recesses on the sides and in a font corresponding to the new sample

6. Fake with recesses on the sides and in the font corresponding to the old sample

It should be noted that the size of the crystal in the first three samples is absolutely the same and makes 3.7 x 2.7mm. We also draw attention to a certain frame around the old sample crystal, which indirectly points to a higher production culture in the old versions.

For a fake without recesses, the crystal is 3.4 x 2.0 mm.

Forgings with the recesses of the crystal 2.0 x 1.6 mm., But even they clearly notice a different technology of fastening the crystal to the substrate - soldering and gluing. Differences in counterfeit technologies point to the great variety of counterfeiters. Also, it will be fair to note that the higher the crystal area, the higher the possibility of heat removal from it and the total area, it is possible to compare very closely (at times) the power on which the product is capable of:

A) 3.7х2.7 = 9.99 square meters. mm

B) 2,0x1,6 = 3,20 sq. mm

     9,99 / 3,20 = 3,12 times

By non-sophisticated mathematical calculations, we see that the area of ​​the crystal in the original product exceeds the area of ​​fake by more than 3 times, which allows you to heat (approximately) 3 times better, which means to get an increase in output power up to 3 times in relation to forgery!

Well, the last, obvious, sign of fake:

Below is a price list for LM1875 from the Texas Instruments manufacturer. Most likely, the manufacturer will not dump their dealers, accordingly, these prices can be considered basic.

Caution Question: How likely is it to meet the new, original LM1875 chipset for sale, at a price below $ 1.36?

Attention answer: There is such a chance if someone in the chain of intermediaries sells himself at a loss!

We hope this material was useful to you and helped to avoid unpleasant waste of money, time and nerves.

If you are interested in the Original and Qualitative product, please contact our store and we will gladly help you!

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