How do I identify the markings on an SMT component and match it up with a part number so I can be a good designer and actually look at a datasheet (and read the whole thing)?

Or identify a part to replace an unknown part on a PCB?


4 Answers 4


Step 1) Identify the package, note how many pins, match up the pins first. Note that sometimes the package pins are underneath the part or extended away from the part. Also get the dimensions of the part with a ruler or (preferably) calipers and match them up with a chart, write them down for a later step. Make sure that when measuring pin pitches (distance between pins) that this is done accurately, it can be difficult to tell (for example) the difference between a 1mm pitch to a 1.25mm pitch. Make sure the measurement is precise, or measure across multiple pins and divide by the number of pins to get the pin pitch.

Package dimensions are standardized IPC-7351 or they can also be found by searching for the package type on google and comparing dimensions. Package dimensions can also be found at manufactures websites in datasheets (or sometimes in files separate from datasheets, it might take some hunting around to find them)

Here are some resources to help you find different packages or use this below:

enter image description here Source: NXP

Step 2) Identify all markings on the top of the component. These markings include: Manufacturer Logo and\or SMT code.

If you are unsure of character differences, make sure these are noted. E.g.: 8 could be mistaken for B. That means if you have A32B it could be mistaken for A328. If you're unsure, you will need to search for both. Here are some sources where you can find them:

You can find many IC manufacturer logo's using this link or the picture below:

enter image description here Source: Electronicspoint

Step still can't find it 3) So what do you do at this point if you can't find what your part is? There are still lots of options. Use what you know about the part.

A manufacture logo or mark on the package can be really helpfull to identify the package. Use parametric searches at the manufacturer's website and package information to narrow down the number of parts. For example: if I thought the part was an opamp with 5 pins and I knew the manufacturer was TI, I would go to TI's website and run a parametric search that looks for all of the opamps with 5 pin packages.

Then start checking datasheets as most of the leading manufactures provide SMT codes in datasheets with the package information. If it is an old part, a search through old datasheets or maybe an email to the manufacturer might be the way to clarify the part. Many manufacturers have also SMD code lists.

The more certainty you have of the package type (or narrowed it down to a few packages) and you think you know what the part does, you can use a distributor search (such as Digikey, Mouser, or Octopart) to narrow down what the part is. This allows you to pull up a datasheet and check.

I have also found extremely vague parts on google just by the package and the SMD number. I tried different combinations of packages (I had two choices), and after some google sleuthing, I narrowed it down to 3 parts. With some testing, I found my part.

If all that doesn't work, and your part is still functional, you might have to do more reverse engineering of the circuit and find the functionality of the part.

For example, if you know its a transistor, you could verify the type of transistor with a multi meter or diodes can be easily determined with the diode mode of a meter.

Because of current leakage in a circuit when it is off, parts such as capacitors or unmarked resistors may need to be desoldered from the board to find the true value (the rest of the circuit is in parallel with the component when the terminals of the meter are placed across it).

  • 4
    \$\begingroup\$ This is a great answer. People should be aware that there is no guarantee that you will be able to find your part. Many SMD packages are too small to include fully identifying information, so sometimes the best you can do is guess by what the component is connected to, maybe measure the voltages at its pins or desolder it and try some tests. \$\endgroup\$
    – BeB00
    Commented Oct 12, 2017 at 19:07
  • 1
    \$\begingroup\$ Does not really work for SOT23 or similarly sized components :( \$\endgroup\$
    – PlasmaHH
    Commented Oct 12, 2017 at 19:13
  • \$\begingroup\$ @PlasmaHH I've never had a problem looking for SOT23, but I've only done it 5ish times. What is the concern there? \$\endgroup\$
    – Voltage Spike
    Commented Oct 12, 2017 at 19:25
  • \$\begingroup\$ And if visual identification doesn't work you can desolder it and probe away at it. (assuming it hasn't failed) \$\endgroup\$ Commented Oct 12, 2017 at 19:50
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    \$\begingroup\$ @laptop2d: they almost never have logos and their marking is at most a few letters that mean nothing. \$\endgroup\$
    – PlasmaHH
    Commented Oct 12, 2017 at 20:01

For devices from TI there is a very useful page available which let's you search the marking codes of the TI chips.

TI Part lookup

Depending on the package there is also a datecode written on it. And sometimes it wraps into a new line.

So my approach often goes like this:

  • enter each line individually
  • enter everything together
  • delete letters from the start until something useful pops up
  • delete letters from the end until something useful pops up

Device Opportunity

I am about to tout a device which true Electrical Engineers will be tempted to look at with suspicion, primarily because it's so inexpensive. Or because it's Open-Source Hardware (OSHW). But it's actually not cheap. It may be composed of cheap components, and cheap materials. But it's full of blood, sweat, and tears. And because it's OSHW, and I can examine the hardware, the firmware, upgrade it, fix it, and enhance it, that's worth it's weight in gold to me. But it also represents a financial opportunity, since there's an obvious hole here (there is no other product like it). Can you fill that hole? Perhaps you'll make money if you make your own closed-source solution. Or (if you speak German), maybe you can make the source code and the manual more accessible to the English-speaking world, and somebody else can fill the hole. I can't do that. Hmmm... Well, onto the device, that should, at least, often identify at least the device type for you (and polarity too).

Disclaimer and Justification for Highlighting this device

I have absolutely no affiliation with the TransistorTester, or the Chinese Clone-Masters who make the inexpensive devices currently sold on Amazon. With a 9-volt battery and a large transformer, I "zapped" myself several times when a young kid in my fathers basement, and I've been fascinated with electricity ever since. I really like this TransistorTester because I think I would be further along if I had just had one as a kid, and it only costs a few bucks. If you think I'm overpromoting this device, it's only because this question was asked more than four years ago -- and nobody else has had anything to offer.

You asked "how do I identify any component". This TransistorTester (component tester might be a better name) is a good step towards deciphering the marks (if any). Please note that some components actually have their marks purposely abraded off to prevent you from figuring out the component. In that case, a device like this one is your only hope.

As for highlighting this device only, I will attempt to add other devices as I think of them. Thank you for pointing out the shortcomings in my answer.

Helpful Device #1: Blue ESR Tester

I got this device, the Blue ESR Tester Kit - Requires Assembly, because it can measure the ESR of a capacitor in-circuit, and because it's relatively reasonably priced at a current price of around $96 USD. But it's also available pre-assembled Blue ESR Tester Kit - Fully Assembly, for about $117 USD. Prices as of 1-26-2022. And it also measures shunts and resistors down to 0.01 ohm. I have no affiliation or profit from this product, and I don't know anybody at Anatek (the manufacturer). If it sounds like I'm promoting it, it's because I wish I found it sooner.

Blue ESR Tester

Helpful Device #2: Transistor Tester

The Transistor Tester was made for identifying parts, uses an Arduino chip (Atmel328P), and is an open source project, so you can get the code and fix it or enhance it yourself. Both versions have pads for testing surface mount components (and Dave of EEVBlog does test a few SMT devices in his video). If you read the manual, you can see how much work has been done to "see how far we can get with very little", though the German-to-English translation really could use some work. For what this question is, "How do I identify any component?", this little device generally gets it done.

Red GM328 DIY Kit

A particular version that I like is the Red GM328 DIY Kit, which I have made several times, and costs less than $40 currently at the above link. Different incarnations behave differently, and I like this kit because I can run through a whole bunch of resistors or inductors in one run, and for putting kits together (like the GM328 kit ;-) it's great.

Red GM328 DIY Kit pic from Amazon

As you can see, it identifies capacitors, BJT transistors, MOSFET's and diodes, and other types as well. The inductance accuracy could be improved, but its main goal in life is identification, so that's okay. It reads frequency, generates PWM, reads voltage -- so, okay, it's the Swiss Army knife of electronic gadgets. Did I mention it's open source?

Several screen shots of the Red GM328

M328 (LCR-T4) Model Transistor Tester (not a kit)

Dave of EEVBlog fame reviewed an earlier version of this device, a M328 (LCR-T4) model component tester here at EEVblog #1020 - Is A $7 LCR / Component Tester Any Good?, although I don't know if Dave ran the calibration step first, so some of the inaccuracies he reports may be overstated. Here is the EEVBlog page itself, which has more related links. This device costs less, than the GM328, even as low as $7, according to Dave.

Yellow M328 (LCR-T4) model component tester

Forum Thread (TLDR)

Absolutely HUGE forum thread and 3 summary videos starting here. I turn the sound off so I can pick up useful information.

Showing forum page 17 testing capacitors, 1:57 on 1-of-3 video

Born in Germany, With Contributions from Around The World!

The device was partially created and/or maintained at this page at www.Microcontroller.net and I here reproduce the download section which tells us the most up-to-date firmware and manuals are on github:

Downloads (English) You can get the most up-to-date versions of software and documentation (english/ttester.pdf) now at GitHub. The documentation is also available in german and russian and czech. Users can download the full archive with "git clone https://github.com/Mikrocontroller-net/transistortester" into a new created transistortester directory. You can update your local copy in the working directory transistortester with the command "git checkout".

Inside the 140-page manual (pretty good) are schematics and lots of information on different modifications that can be made, upgrades, using different microcontrollers (and how to use it, of course.)

Screen shot of page 1 of manual

The Unheeded Note to the Chinese Cloners

Pretty much all of the Chinese clones don't give you any of this information, nor do they admit that it is an open source project, and they certainly don't give you the manual. You can tell that the creators are frustrated with being ripped-off and misrepresented, but they are actually very gracious:

Hint to Cloners and Sellers 中文 Dear Transistortester Cloners and Sellers! ... We don't mind if you produce and sell clones of the Transistortester. It provides an inexpensive great little tool for electronics enthusiasts and beginners, but PLEASE note the links to the project's webpage, source repo and documentation. You would add more value by giving users that information to be able to update the firmware and to understand all the features. If you do any modifications to the firmware, please send us a copy for the repo. And if you would send us your Transistortester clones, we would be able to keep the firmware as compatible as possible. Don't forget, this is an OSHW project! ... Best regards, Transistortester team

Pitch for Give-Back

If you enhance or fix your TransistorTester firmware, we would all appreciate it if you would please contribute back to this OSHW project. And if you're on an Amazon page doing a review, please consider putting in a link to the www.mikrocontroller.net page and the github page for the manual.


I have multiple of both of these TransistorTesters and can vouch for them, that they seem to work fairly well.

TransistorTester Schematic, Fig 2.1, from Page 11 of Manual.

Original Version from Elektor Magazine

This semiconductor analyzer device was listed as an inspiration of the Transistor Tester, and it uses the PIC16F876-20/SP microcontroller, and I list it because you can also build yourself one of these.

SC-Analyzer 2005 Discrete semiconductor components intelligently tested

Bipolar transistors, FETs and diodes are electronic components that are kept in stock almost everywhere. It is not uncommon to find unknown types that were bought cheaply at some point, or they were removed from disused circuits. The tester provides information about the pin assignment and the most important properties of the unknown objects. It is also not a problem for him if the test candidates have an SMD design. The following important parameters are determined: current gain hFE for bipolar transistors, UTH, IDSS and RDSON for JFETs, the threshold voltage for MOSFETs and the dependence of current and voltage as well as the reverse current for diodes. The SC analyzer clearly shows the measured data on an LC display.

  • 2
    \$\begingroup\$ This does not do much to answer the question. It sounds more like a product promotion than anything else. IMO this is not the right place for your post. \$\endgroup\$ Commented Jan 26, 2022 at 5:14
  • 1
    \$\begingroup\$ @Microservices Please do these things so the post is not spam 1) Actually answer the question 2) Edit the post so it doesn't just promote products 3) provide your relationship to the linked products \$\endgroup\$
    – Voltage Spike
    Commented Jan 26, 2022 at 6:06
  • \$\begingroup\$ Please also read: electronics.stackexchange.com/help/promotion \$\endgroup\$
    – Voltage Spike
    Commented Jan 26, 2022 at 6:08
  • 1
    \$\begingroup\$ @VoltageSpike - I think you're confusing the fact that I'm excited about electronics with thinking that I am promoting these devices. I have absolutely no affiliation with the Blue ESR Tester or the TransistorTester or either of their companies. It's been four years since this question was asked. Instead of tearing me down, why don't you just show me up. The fact is that this is a very hard problem. And the devices I have presented are helpful when you can't look up the hieroglyphics, or worse yet, when all marks have been ground off the part, to specifically prevent part identification. \$\endgroup\$ Commented Jan 26, 2022 at 15:52
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    \$\begingroup\$ This needs more focus. Why is there a huge picture of the starting page of the manual? Why is there a note to chinese cloners, who don't care anyway, a pitch for give back, a caption just to enjoy. I think it's a useful answer in the sense that pointing people to tools which can be helpful identifying components, but currently it feels bloated. Maybe the captions should be for general device categories, list what they help with and then only have some example devices listed without too many pictures. People interested will probably find everything related then, when they go hunting for it. \$\endgroup\$
    – Arsenal
    Commented Sep 8, 2022 at 15:12

Micron provide a Micron FBGA and component marking decoder which looks up their FBGA marking code.

E.g. just searched for the RW167 FBGA code for what thought likely to be a serial flash and the tool returned a link to Serial NOR Flash Memory PART MT25QU256ABA1EW9-0SIT


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