Cheap DMM Transistor testers? - Page 1
Forum section: electronics / testgear

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 09, 2016, 11:48:55 pm
content: So I have a few DMM's all at least $100 and up, the other day I got a coupon for one of thoseChinese Centech 7 function DMMsfor free. I wasn't even going to pick it up but I ended up going in to the harbor freight for a set of jewelers loops and ended deciding to get my free meter because it would be the only one I own with a transistor tester. I haven't used it yet but I am under the impression it can help you sort between NPN/PNP and tell you the gain or hfe? I remmber some EEVBlog video where Dave passingly said the transistor testers on DMM's are worthless.I was wondering what exactly the deal with these things are, seems like they should be on every meter unless they are totally useless and if they are then why? I had thought about replacing one of my lower end DMM's with this inexspensiveBK DMM, oddly it seems to be the only one that can test transistors and is one of there low end models. If the tester on the the 5 dollar meters is worthless, maybe the BK's is better if so worth the purchase just to get the tester?

author: uncle_bob
author_rank: Unknown
timestamp: May 10, 2016, 12:08:51 am
content: HiWell, let's see ... transistors have three leads. To test one anywhere near properly, you need to bias (say) the collector relative to the (say) emitter and inject a measured current into the base. You then measure the collector current relative to the base drive to get Hfe.Cheap / simple approach:Short the collector to the base, see if it looks like a diode.Needless to say, the first approach is a bit complex to implement. The second one is drop dead easy. The problem is that the second one only tells you that in some way the transistor looks like a diode. There can still be a lot wrong and you have a diode in there somewhere ....Bob

author: LaurentR
author_rank: Frequent Contributor
timestamp: May 10, 2016, 01:00:02 am
content: Good quality, relatively inexpensive transistor (and more) testers:DCA55 or DCA75 (DCA Pro)http://www.peakelec.co.uk/acatalog/jz_dca55.htmlhttp://www.peakelec.co.uk/acatalog/dca75-dca-pro.htmlAccording to several threads on the forum, having the small 3-pin transistor connector makes it hard/impossible to be CAT rated, so most proper DMMs skip this. It is also not all that useful for most people.

author: ez24
author_rank: Super Contributor
timestamp: May 10, 2016, 02:42:46 am
content: Quote from: LaurentR on May 10, 2016, 01:00:02 amI do not think this meets OP's requirement of "cheap" even though a good product. Since the OP is in the US, here is a US linkhttp://www.amazon.com/Peak-Atlas-DCA55-Semiconductor-Analyzer/dp/B005NIR8G8/ref=sr_1_1?ie=UTF8&qid=1462848066&sr=8-1&keywords=peak+transistor+tester

author: crispy_tofu
author_rank: Super Contributor
timestamp: May 10, 2016, 02:51:08 am
content: Maybe this might work for your needs? Although it isn't a DMM...https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/

author: MrSlack
author_rank: Frequent Contributor
timestamp: May 10, 2016, 06:09:13 am
content: I keep a UT33A around for transistor hfe measurement. Quite handy. This is a go/no go measurement more than anything though.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 10, 2016, 08:52:35 am
content: Quote from: uncle_bob on May 10, 2016, 12:08:51 amThe way I do a "go-nogo" test is thus:-For an unknown transistor,first check which lead is thebase,by noting the diode junctions.Thebasewill have junctions with both of the other two elements.Whether they are NP or PN will identify the device as PNP or NPN.Assuming an NPN for now,place the +ve DMM lead on one of thenon-baseleads & the -ve on the other.Now "spit" on your finger & place it between the +ve connection & thebase.You will see a reading on the DMM (in diode test mode),because the transistor is partially turned on.Note this reading.Reverse the DMM leads,Repeat the test,& again there will be a reading.The highest current (lowest resistance) reading shows which lead is thecollector,which is theemitter,& whether the thing works.

author: elverado
author_rank: Newbie
timestamp: May 11, 2016, 02:48:54 pm
content: I looked at the Peak Atlas products mentioned above and my impression is that they tend to be used by factory control and HVAC field tech types for quickly IDing failed parts without needing to get into further detail on how boards are designed. So they tend to be priced and built around that kind of robustness but are not cheap. After finding that out of my price range I was happy to find what I consider the 'open source hardware' option and bought and built this kit a few months ago and am very happy with it:http://www.ebay.com/itm/141767800169It's a cheap kit based on a lot of background research and design that I saw complimented here -https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/Here's the background (use google translate):http://www.mikrocontroller.net/articles/AVR_TransistortesterIAnd manual PDF:http://www.mikrocontroller.net/attachment/164956/ttester_eng104k.pdfI used it to successfully identify a few dead transistors on my Tektronix 465 O-Scope and it quickly paid for itself.Edit: here's another buying option, fully assembled:http://www.amazon.com/Yosoo-Display-Transistor-Cymometer-Generator/dp/B00OOQC2E8

author: QuantumLogic
author_rank: Contributor
timestamp: May 11, 2016, 07:39:37 pm
content: As already mentioned, just get one of these:http://www.ebay.com/itm/271821270337Works really well for pretty much any component, transistors and MOSFETs included. I love mine.

author: ez24
author_rank: Super Contributor
timestamp: May 11, 2016, 08:02:51 pm
content: Quote from: QuantumLogic on May 11, 2016, 07:39:37 pmMaybe our HK seller has these. I forgot his nameBut it looks like this one ships from the US (if OP is in the US)http://www.amazon.com/Yosoo-Display-Transistor-Cymometer-Generator/dp/B00OOQC2E8/ref=sr_1_1?s=industrial&ie=UTF8&qid=1462996765&sr=1-1&keywords=transistor+testerPrice range is within a cheap multi-meter, so it seems this fits the "cheap" requirement

author: MrSlack
author_rank: Frequent Contributor
timestamp: May 12, 2016, 05:45:43 am
content: Watch out for these. I've had them give vastly different measurements on the same device if you take 2-3 samples in a row.

author: crispy_tofu
author_rank: Super Contributor
timestamp: May 12, 2016, 06:23:07 am
content: Quote from: ez24 on May 11, 2016, 08:02:51 pmFranky, useriloveelectronicson the forum.

author: mzacharias
author_rank: Frequent Contributor
timestamp: May 12, 2016, 07:49:33 pm
content: I use DMM hFe checkers fairly often in audio work. Seems if the gain of a differential pair transistor is mis-matched too much, a DC offset, sometimes intermittent, will result.Additionally, I have seen some Korean KSC types on some newer units which test good in static tests but which have "zero" gain. Again, DC offset is the result in these units.High on the list of suspects on the later model Denon, Marantz, Pioneer types.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 25, 2018, 11:26:33 pm
content: Quote from: rwgast_lowlevellogicdesin on May 09, 2016, 11:48:55 pmEither keep the HF for transistors or grab a Mega328 based module off flea bay. starting under 20 bucks. They measure all kinds of components. You can hook the three leads up any old way and it will tell you pnp or npn and the beta. It automatically identifys all kinds of devices. For a few bucks more you can get it in a case. They measure FETs, SCRs, triacs, capacitors, inductors and capacitor ESR. That is a lot that you will not find in a DMM at any price. They are all over ebay and Amazon.Sent from my SM-G900V using Tapatalk

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 28, 2018, 02:00:37 pm
content: Quote from: uncle_bob on May 10, 2016, 12:08:51 amThere are 2 "diodes" in there in a bipolar transistor.. Using an old analog meter that pushed enough current, I would check both ways CB and EB. I would get around 10 to 15 ohms one way and very high or infinity, the other. Then I would check CE and a good one is high both ways. Power transistors often fail CE. I found plenty of bad ones this way. A transistor checker is pretty handy as it runs a simple beta test and any of the above bad readings wil produce no gain it one quick test.Sent from my SM-G900V using Tapatalk

author: David Hess
author_rank: Super Contributor
timestamp: August 29, 2018, 03:32:19 am
content: Three lead DMM transistor tests just measure hfe and will not always reveal a bad transistor. Using the diode test function to check each junction and then the change when the collector is shorted to the base is more reliable.

author: rhb
author_rank: Super Contributor
timestamp: August 30, 2018, 01:56:05 pm
content: The diode test will let you identify the leads and the polarity. The BC junction has a lower drop than the BE. The socket will then measure hFe. But actual mileage may vary as the sockets are not very good on some versions.

author: mzacharias
author_rank: Frequent Contributor
timestamp: August 31, 2018, 12:39:51 pm
content: I picked up one of these combination testers. Not so cheap as the bare board models, but much handier, still pretty cheap, and you can use more standard test leads if you like. Tests, transistors, digital transistors, coils, caps, resistors, FET's MOSFET's, etc.Identifies component leads as all these types do.https://www.ebay.com/itm/BSIDE-ESR02-Pro-Digital-Transistor-Tester-Diode-Capacitance-Resistance-Meter/173392022021?epid=10019620142&hash=item285ef84a05:g:QxwAAOSw~RVaMkRp

author: rhb
author_rank: Super Contributor
timestamp: August 31, 2018, 03:24:26 pm
content: That looks pretty useful for SMD parts.