Different ways to test transisors - Page 1
Forum section: electronics / beginners

author: BigFarma
author_rank: Newbie
timestamp: June 20, 2023, 09:48:21 am
content: Hello! I am setting up a home lab. I am curious how many ways there are to test transistors. I know with capacitors if you just measure capacitance your going to get a lot of caps that test well but are actually faulty. Therefore you need to test not just capacitance but esr, leakage, etc. Is it the same for transistors? How many tests are there to determine a transistor is in working order and what is the best way to go about this? Thanks!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 20, 2023, 11:05:49 am
content: All sort of ways to test transistors.To start with get a component/transistor tester.They are relatively cheap and there are threads here dealing with lots of them. I use a BSIDE at the moment.Search the Test Equipment Section, look for Transistor Tester, lots of suggestions and evaluations

author: Zero999
author_rank: Super Contributor
timestamp: June 20, 2023, 01:59:50 pm
content: What sort of transisor: PNP, NPN, P-MOSFET, N-MOSFET, P-JFET, N-JFET, IGBT?

author: David Hess
author_rank: Super Contributor
timestamp: June 20, 2023, 03:03:50 pm
content: For bipolar transistors it is usually sufficient to test the forward voltage drop of the two junctions to verify functionality, however bipolar transistors can fail in subtle ways which require testing of current gain, saturation voltage, and collector breakdown voltage. In extreme cases a curve tracer is required to identify a defective bipolar transistor.For JFET transistors I would test channel resistance, gate forward voltage, and gate leakage.For MOSFETs I would test channel leakage, gate leakage, and channel resistance.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 20, 2023, 03:07:13 pm
content: Buy yourself one of these $10 widgets They cost less than the sum of their parts, magic! "LCD Display LCR-T4 Transistor Diode Capacitor ESR LCR Meter MOSFET PNP Tester" or similar from eBay. Buy one that comes in a ready made case. Very handy. They are such amazing VFM and they are pretty accurate too. Get one now!Even our Dave liked itwww.eevblog.com/2017/09/11/eevblog-1020-is-a-7-lcr-component-tester-any-good/

author: BigFarma
author_rank: Newbie
timestamp: June 20, 2023, 06:50:57 pm
content: Quote from: Terry Bites on June 20, 2023, 03:07:13 pmNice video, neat little tool. I kind of skipped over these and was looking at the Atlas Peak DCA55 and DCA75 Pro, but if I can get most of the functionality for 5-10% of the cost that is quite tempting

author: BigFarma
author_rank: Newbie
timestamp: June 20, 2023, 06:59:27 pm
content: Quote from: Zero999 on June 20, 2023, 01:59:50 pmCurrently I have some IRF740 mosfets that need testing, but I would like to get the gear to test the broadest range of transistors within reason.

author: BigFarma
author_rank: Newbie
timestamp: June 20, 2023, 07:14:25 pm
content: Quote from: Wallace Gasiewicz on June 20, 2023, 11:05:49 amLooks like a lot of people are using the BSIDE unit. Thanks for the suggestion

author: james_s
author_rank: Super Contributor
timestamp: June 20, 2023, 07:24:57 pm
content: The most widely useful tool for testing transistors is a multimeter with a diode test function. BJTs can be tested as a pair of diodes, with mosfets you can test the body diode and usually when they fail they fail shorted and the diode test feature will catch that too. If you want to test the gain or other characteristics then you need something fancier but I rarely find this to be necessary, most of the time I'm doing repair work and just want to know if a transistor is shorted.

author: BigFarma
author_rank: Newbie
timestamp: June 20, 2023, 07:34:12 pm
content: Quote from: james_s on June 20, 2023, 07:24:57 pmI am also doing repair work and using a DMM with diode test function. I'd just like to make sure I'm not missing other paths to component failure, similar to my capacitor analogy. If that's how they die then great, less money spent. But David Hess pointed out some other 'suble ways to fail'Quote from: David Hess on June 20, 2023, 03:03:50 pm

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 21, 2023, 12:12:47 am
content: Someone suggested an Atlas. I have used one and they are nice. The case is stronger and the leads and connectors are good.I think getting one of these things that test transistors and other parts like caps and inductors is the best idea (BSIDE, Atlas etc). After you have spent maybe $10 to $30 you can decide if you need something more involved. Someone gave me an old BK curve tracer. It works fine but you almost have to have the thing set up somewhere to use it regularly. It is a pain to have to get it out and set it up, so almost all the time I use my Fluke with a diode tester as others have suggested, or use the component tester.If you really need to "match" transistors then you probably need a curve tracer although measuring the drops across junctions and resistance of JFET channel with a multimeter will help match these components. A curve tracer is usually expensive (unless someone gives you one) and very hard to use with a modern oscilloscope, at least that is what I have found.There are special circumstances you need different equipment for.If you really need to measure leakage on high voltage caps from tube equipment, you need a high volt tester, like the old Heathkit ones. They work fine and are a lot cheaper than the new high voltage testers.The component testers will not measure very low cap and inductance values, for that you need an LCR meter.Start with the component tester you decide looks best, you will need it anyway, then start buying fancier equipment, then you will qualify for free therapy on the TEA thread: Test Equipment Anonymous. HA!!

author: james_s
author_rank: Super Contributor
timestamp: June 21, 2023, 12:38:48 am
content: Quote from: BigFarma on June 20, 2023, 07:34:12 pmOther failure modes are possible, especially in small signal stuff, but when power transistors fail they usually fail shorted. Those little component testers are cool and very handy for sorting through junkbox parts but they normally can't be used in-circuit. Trying to do in-circuit testing with a multimeter isn't foolproof either but most of the time it can give you a good idea of what's going on.

author: EPAIII
author_rank: Super Contributor
timestamp: June 21, 2023, 01:41:25 am
content: I have had to test and tested thousands of transistors over the years of my career. Almost all of those were tested out of circuit (at least two leads lifted) with a VOM - an analog VOM (Simpson 260 in most cases). And up until a year or so ago, James' answer below would have been mine with one exception. That exception is for BJTs I also checked the E-C pair, both ways. There were a few times when both junctions checked OK, but the E-C was open or shorted.BUT today I have recommend one of the inexpensive component testers that are now common on the web. Here is just one:https://www.amazon.com/Organizer-Multifunction-Transistor-Capacitor-Inductance/dp/B07T6FKHM6/ref=asc_df_B07T6FKHM6/?tag=hyprod-20&linkCode=df0&hvadid=385590136039&hvpos=&hvnetw=g&hvrand=8259130114963989386&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9027887&hvtargid=pla-911296628637&psc=1&tag=&ref=&adgrpid=73872202530&hvpone=&hvptwo=&hvadid=385590136039&hvpos=&hvnetw=g&hvrand=8259130114963989386&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9027887&hvtargid=pla-911296628637I bought one and was so impressed that I bought a second one for my second electronic bench. I have added a mini-telephone jack to them and made up sets of clip leads so I can connect to parts on PCBs. They are a great idea. They test many components, including BJTs, FETs, resistors, capacitors, diodes, inductors, etc. For the price, you just can't go wrong. I wish I had one 50 years ago. It would have saved me countless hours of work.From my experience testing and using these testers, I strongly recommend them. They would have caught almost every bad part that I ever encountered in over 45 years of professional electronic repair work.Quote from: james_s on June 20, 2023, 07:24:57 pm

author: BigFarma
author_rank: Newbie
timestamp: June 21, 2023, 01:51:25 am
content: Quote from: EPAIII on June 21, 2023, 01:41:25 amQuote from: Wallace Gasiewicz on June 21, 2023, 12:12:47 amThank you everybody! I just bought a DE-5000 and i will get the tester that EPAIII and Terry Bites suggested or the BSIDE Wallace Gasiewicz mentioned. (leaning towards the BSIDE) I believe that should be a pretty strong startI doubt ill need a curve tracer for any of the projects currently on the bench but if that day comes ill be looking at the Atlas Pro or something similar that has computer interface. I was planning on doing all testing out-of-circuit but its good to hear in-circuit can be reliable as well with some of these tools.

author: Zero999
author_rank: Super Contributor
timestamp: June 21, 2023, 08:03:33 am
content: Quote from: BigFarma on June 20, 2023, 06:59:27 pmThe body diode (drain to cathode and source to anode, for an N-channel MOSFET and the reverse for P-channel) is the easiest test to perform. Always perform it with the gate connected to the source, otherwise stray electric fields can turn on the MOSFET and interfere with the test. The gate shouldalso be open circuit, with respect to the drain and source.Note the above tests will only show it works. They won't spot fakes i.e. a 2N7000 chip inside a package marked with IRF740.