#131

A back to basics video showing several ways to test BJTs, or bipolar junction transistors. The example shown is an NPN transistor. To test a PNP transistor, simply reverse the leads of the meter. The use of an analog meter / VOM (Simpson 260) as well as a Fluke digital multimeter DMM is shown, as well as a couple of Heathkit transistor checker/testers.

[@swingmanic]

Nice to see a good old faithful Simpson 260..I've had mine for over 35 years and it's still a great workhorse!!

[@neilsheldon8355]

Thanks, Allen, for your always super video. Great info. One note; I've used the Simpson 260 for decades ... love 'em. One nice feature that I'm sure you are aware of, but others may not know, is the DC+ and DC- switch. By simply connecting the leads to, say the Base, Emitter leads, and switching between the DC+ and DC- back and forth, you're effectively reversing the test leads, without having to move them. And then, connect up the Base, Collector leads, and make the same switch test (DC+ and DC-) with one direction conducting, and the reverse mode, not conducting. I also typically connect the Collector , Emitter leads, and do the same test (DC+ and DC-) to see if there is any leakage. I've verified many good transistors that way, as well as finding some culprits hiding away on the circuit board somewhere. Hope that is of assistance. 73, Neil, K7WK

[@Roy_Tellason]

Mine is an older unit that doesn't have that functionality. Instead there's "DC-AC-Output" the last one of which just capacitively couples the input signal.

[@SIXSTRING63]

Thanks so much for all the great educational videos. I’ve learned so much from you, Mr. Carlson’s Lab, TRX Bench and a few others. I’ve taken on this hobby late in life after being in the mechanical engineering end of things for many years. I always dabbled in electronics and started a home study course in the early 90’s while between jobs. I was doing quite well but had a good job turn up as a tool and die maker to which I was quite good at so that put the career change to electronics on hold for a long time. For the past ten plus years I started repairing my own guitar amps and such and got the bug to learn more and more. Thanks to all of you who share your vast knowledge and wisdom. It’s a very addictive and satisfying field of endeavor to say the least.

[@andrew_koala2974]

@ SIXSTRING63 Good to hear you developed an interest in Electronics. I developed mine when I was two years old by sticking my mothers crotchet needle into the AC Mains power-point live terminal. >. and LIVEd .. and I remember being thrown across the room. At age 8 my mothers brother (an Electronics Engineer was teaching me TV and Radio repair and to drive his Hillman Minx. That was in 1958. By the end of 1969 I graduated with a degrees in Electronics Engineering and Electro-Mechanical Engineering whilst then working fro PHILIPS.My then mentor, a very hard task-master made my head hurt, and I could have strangled him, though he was tough I never forgot what he taught me. He is still alive today, I see him often as he resides within 15 minutes drive from my home, and we have been friends for decades. I can recommend for you: EEVblog CHANNEL: kzbin.info/door/2DjFE7Xf11URZqWBigcVOQ EEVblog Main Web Site: www.eevblog.com 2nd EEVblog Channel: kzbin.info I have known Dave for decades also as we were both then members of TETIA -Television and Electronic Trades Institute Australia TESA - Television and Electronic Service Association

[@Pwaak]

Back to basics lessons are very, very helpful. Thank You!

[@Beretta96Dan]

Thanks for the refresher course on testing bipolars. I look forward to your videos. Thanks!

[@ve6kk]

Excellent clarity Alan. I also demo the "wet finger test". With the Simpson Ohmmeter +ve red lead on the (supposed) collector of an NPN and the black lead on the emitter, a wet finger base to collector will show a significant deflection, much more than finger leakage alone. Reversing C and E will yield much poorer conduction, showing a very low Beta - current gain. Fun stuff! 73.

[@abeleballestri612]

Very gut explanation how to check transistors either PNP or NPN . Also grateful for the instrument suggested and their performances. Thank you very much. A Ballestri Switzerland.

[@FrankBartson]

thank you! this was a good refresher for a old dog from rets detroit mi 1978 :-)

[@ernieschatz3783]

Very good to get it down to the basics. I normally use my Peak Altas checker, which completely breaks down everything about the transistor, including which leads are c, b, e. In those times were an automated tester isn't with you or maybe you don't own one YET, It's very useful to know enough basics to use what's on hand. That said, Peak product is the bees knees most of the time, as it eliminates guesswork and checks the item much more quickly, but there are a few (very few) instances where the specific component are not in its internal database.

[@Agent24Electronics]

Very nice video, clear and easy to understand

[@mikesantarini3617]

This a great video. It would be interesting to see this on a germanium transistor

[@uhfnutbar1]

good video sir:) it took me a few videos before i found yours , some people just dont get that showing the meter makes lot easier to understand then there mumbling s :)

[@txsharpshooter85]

Great video. I'd also like to see some mosfet testing info. Thanks for posting.

[@AndRamons]

Very good video.

[@RadioFixer]

Excellent video 👍👏👏 thanks for sharing.

[@TechTins_Projects]

Another top class video! If you had no markings at all and no data sheet, I suppose you could work them all out, by measuring all the different combinations of possible PN drops. That would make a nice short video!

[@DeniskaNYC]

Thanks for sharing. Great video for beginners !

[@lonzerwalker6569]

DeniskaNYC w

[@Radionut]

Thanks for the great how to

[@nickymardian4941]

Hi...if E and C dont conduct each other wich mean good transistor right?? i had bc857/847 and mmbt3906/4 smd, BC transistor E and C lead conduct each other all of them, and mmbt dont cunduct, so mmbt transistor is good??

[@pyotrleflegin7255]

Nice tutorial -- thank you.

[@jix177]

Very interesting! Thanks for sharing.

[@danielrine3103]

Hi, first time view, great video thank you for sharing this with us....

[@RS_83]

Thank you very much,sir!

[@waynegram8907]

How can you test and measure the transistors Re Regeneration? I'm not sure but what is the emitter regeneration is doing to the voltage, current and beta?

[@jeanious2009]

Just picked up one of these, came from Canada...lol. Can you do a vid on how to calibrate them, test to make sure their working properly.. From what I've read several had the 1/10x switch soldered backwards (may be an early revision in the original manual).

[@Inquire98]

"Thank You", thank you very much

[@richardgoebel226]

This is an excellent back to basics video. Will you be making a sequel with oscilloscope curve tracers and possibly testing MOSFETS, too?

[@richardgoebel226]

Oops, just spotted the next video you produced.

[@treadmillrepair754]

I am in electronics for 40 years and I find the best transistor tester ever made. This is the Peak Atlas DCA75 pro. Try it. Cheers.

[@w2aew]

Yes, those Peak Atlas tests look really nice - I've been thinking about picking one up.

[@sssttt6533]

677mV forward voltage between base and emitter. 680mV between base and collector. When I test a transistor I always notice that the forward voltage between the base and emitter is more than the voltage between the base and the collector. Am I wrong? I used to think that I could identify the emitter and collector in that way

[@w2aew]

Sss Ttt I think this will depend a bit on the particular transistor type, so it might not be a reliable way to determine the terminals.

[@daftbeyer]

It might be that the emmiter region being heavily doped (rich in electrons for an npn transistor) creates a stronger electric field, this being seen as an increase of a few milivolts.

[@toreno49]

hi what battery are you using in your it-3127? will it use regular c type ?

[@w2aew]

It uses a pair of C cells in series.

[@Roy_Tellason]

On using a Simpson 260, the Rx1 range might not be such a good idea. The spec on that meter says that current on that particular range can be as high as 625mA! This would be a bit much for some devices. I have that first Heathkit tester you showed, it was given to me with a *very* leaky battery in it (a single C cell, the only thing I have here that uses that size). If you're going to leave a battery in it either don't leave the test leads plugged in or clip them to themselves to prevent them shorting out. Leakage tests are something that I think is a bit of a holdover from when germanium devices were common. While I have a few in my parts boxes, I don't see me using them any time soon. :-) In addition to the above tester, I also have a small one sold by Radio Shack. There's a switch to turn it on and select polarity, and then a knob that you rotate. When the light comes on you can read the (relative?) gain by the knob position. I was recently given a larger version of the same kind of unit, but since I don't use the first one much I gave it to my brother...

[@James_Bowie]

With some analog meters, when in Ohms mode, the red test lead is in fact negative and black lead is positive.

[@MantisRay861]

What does it mean if a transistor has a base to emitter voltage drop if only 0.187 v? A known good transistor of same type has 0.68 v drop B-E. I take it that it’s gone bad, would that be correct to assume?

[@w2aew]

Sounds like a failure to me. Base-emitter short.

[@MantisRay861]

w2aew Ok, thanks. And great video as always!

[@dwightparaiso6798]

Nice info

[@snaprollinpitts]

cool, thanks, I gotta look for one of those things mike

[@fijabo]

Do the 0.680 reading corresponded to the base-emitter junction and 0.677 to the base-collector junction? Typically, one juction will always read lower to identify all terminals of the transistor.

[@RaulHernandez-lg5nw]

The emitter-base will always be higher than the base-collector reading for bi-polar transistors!!

[@YellowsourceOrg]

Very nice video again. What about a simple D.I.Y transistor curve tracer for the oscilloscope with a few trace-lines? The w2aew way, maybe? Commercial tracers are out of the question, because they are much to expensive. If not, no harm done. I still will love your videos! Big thumbs up.

[@peterfardell9267]

Really useful thank you. However a note of caution when using an analogue multimeter. With many analogue multimeters the internal battery connection is plus to the black (negative) lead and red is to the negative lead.

[@johnywhy4679]

i'm confused. You show meter deflection with positive probe on base of NPN, and neg probe on E or C. But no deflection if you reverse your probes. I'm getting opposite results, with a 2N3904. Meter deflection with neg probe on base, and pos on E or C. What am i doing wrong? thx

[@w2aew]

It is possible that your meter has the reverse polarity on the test leads when in resistance measurement mode. You can verify this with a 2nd meter. Also, validate your measurements on multiple transistors to be sure.

[@rbjassoc6]

That is because the guy is WRONG ! What he is explaining is ONLY if you have a Diode mode on your meter! Then the meter puts CURRENT through the transistor. If you just use ohms it is the reverse!

[@johnywhy4679]

i got a different answer on SE. Something to do with 'Traditional analogue meters were reversed'. electronics.stackexchange.com/a/340108/65001

[@alanwolke6253]

This is what I stated. Some analog meters are reversed polarity when in resistance (ohms) mode, some are not.

[@jonmichael02302]

I can't believe this video got 6 dislikes? Jealous idiots.... excellent video!

[@conjering]

What is an acceptable leak for an AC128 Transistor? Great video BTW.

[@w2aew]

Given that's an old Germanium PNP transistor, I'd expect leakage currents of a few hundred microamps.

[@conjering]

Can you please make a video going over that?

[@kabandajamir9844]

So nice

[@Kennynva]

I dont get the germanium tranys Im checking..they will check with a base ofsay 60 on my tester then I can reverse the leads swap collector for emitter and it will read 20 gain on the same tester...is this transistor bad..or is it different for germanium's???thanks.. KE4HVE

[@w2aew]

+Kennynva T. All bipolar transistors will work (poorly) when connected backwards (swap collector and emitter).

[@Kennynva]

so you will get a reading when C and E is reversed on a germanium trany...thanks.

[@tomference4618]

..clear, being old school I remembered the old Simpson from my 1969 class!

[@thebreretons]

Think it's worth mentioning that a very popular range of analogue meters, AVO 8 series (and my own AVO 73) carry a positive voltage to the black test lead when on any ohms range...opposite to your Simpson.

[@w2aew]

Very good point - and something worth checking out on the meter you intend to use for this purpose.

[@rudiyang7790]

Thank you a million times sir...and greetings from Jakarta Indonesia recently I salvaged a H945p transistor from a very old stereo. I'm going to use it for my microphone preamp project and searching a way to test it because it's an old parts...now I found the way from your video.. btw.. can I clarify with you that my H945p transistor can be use for microphone preamp? because I'm uncertain that it can be used for it and risking a damage to my microphone or my output device thank you again sir

[@w2aew]

Looks like an ordinary general purpose NPN silicon transistor. Should be fine in your application with a properly designed circuit.

[@rudiyang7790]

w2aew thank you for replying sir,.. I learned that transistor is a diode from this video sir... planning to watch other videos.. I just learned that electronic is interesting and found out late,.. I'm currently 41.. and God bless there's people like you share the knowledge.. thank you

[@devilmastah]

Also would be in for a mosfet video

[@GeorgeTsiros]

mosfets, please! :D

[@Kennynva]

How do you test for a leaky transistor with a multimeter?

[@w2aew]

+Kennynva T. In general - apply a DC bias across the collector-emitter or drain-source with the base/gate biased off, and measure the current that flows.

[@Kennynva]

+w2aew I see that heathkit for sale..and think I can get it for like 18$ the IT 18.

[@Kennynva]

I have the Micronta dynamic checker now..but dont know how to check the leakage..I am using or checking germanium transis..now..form an old Harmon Kardon stereo..the radio has AM and plays fine but ZERO on FM...not a sound, no bodys home..

[@jon123423]

Or you can go modern at look at items like this: www.ebay.co.uk/itm/Peak-Atlas-DCA55-Atlas-Semiconductor-Component-Analyser-/112052577165?hash=item1a16daa38d:g:likAAOSwRgJXgitg or perhaps below (which does lot more): www.ebay.co.uk/itm/172225104646

[@MrMac5150]

The teacher.

[@devilgabbar1956]

It,s a true test of transistors

[@kanarimentos7056]

good

[@electronicatutorial]

I have a Peak Atlas Pro and is a very nice automatic tester to test 3 and 2 pins devices it can also be connected to a PC to show the curves. /watch?v=41yDmZOXFLA

[@macknumber9]

Can you test this in circuit or do you need to desolder and test it off circuit?

[@w2aew]

In-circuit testing can not always give you reliable results because of the unknown influence of other components in the circuit. Unless you know the schematic and then know what to expect from the remaining connected components, in-circuit test can only sometimes give you an indication of a gross failure (open or short).

[@macknumber9]

@w2aew I am testing a relay and on the power supply side I get the 12vdc...all is good there...but the other side of relay I am seeing 6vdc...I am thinking there is an issue with the NPN transistor....any specific tests I can do? This is all over my head but I'm trying my best to comprehend it. I was told to short the base to ground so the transistor is not functioning at all and should not be conducting collector to emitter...if I do this I should see the 12vdc at the collector side of the relay coil...if I don't see 12vdc and I see something lower then it confirms the transistor is bad...is this correct?

[@w2aew]

@@macknumber9 Yes, as long as there is nothing else connected to that end of the relay coil that could be pulling current through it.

[@macknumber9]

@w2aew yeah nothing else is connected....if I see 12vdc doing this test then what would you test next? The actual base voltage reading while in operation? I would expect to see .7v or higher at the base...if I see less then the transistor would not be at fault but possibly the transistor is not getting the right voltage because of anything before it? Bad resistor etc

[@w2aew]

@@macknumber9 Measure base-emitter voltage when "on", should be about 0.6 to 0.7V or so. Is there any resistor between emitter and ground?

[@tajlingchin2553]

1- What are the maximum readings of each transistor when using the "diode" option? 2- If the readings are "acceptable"....gives it us the security that the transistor is in good consition? Thanks😊

[@w2aew]

Nearly all silicon bipolar transistors will show between 500mV and 900mV. Anything lower than 500mV may indicate a shorted transistor, or possibly a Germanium transistor. Anything over 1V probably indicates a problem. If the readings are acceptable, these are signs that the transistor is *probably* OK, but there are failure modes that won't show up with this simple test (high leakage, beta degradation, high-voltage breakdown, etc.).

[@tajlingchin2553]

@@w2aew thanks for the explanation 😃. There is an other thing i'm sitting with....does a transistor has TWO- or THREE reading? I have a Hometheatersystem with a subwoofer issue. It goes into protection mode. I removed some main transistors and checked them with a DMM. The A1941/A940 and the C5198/C2073 give me two readings. But the L7805CV/L7815CV and L7915 CV give me three readings.....🤷🏽

[@w2aew]

@@tajlingchin2553 The first four devices are likely 2SA1941/2SA940 and 2SC5198/2SC2073 which are all silicon bipolar transistors. However, the last three parts are actually 3-terminal voltage regulators. The L7805CV is a +5V voltage regulator, and the L7815CV and L7915CV are +15V and -15V voltage regulators respectively. These can't be testing like a bipolar transistor.

[@tajlingchin2553]

@@w2aew thanks for the explanation. I've learned something new 😃

[@tajlingchin2553]

@@w2aew i did some more researches on the circuitboard and saw that the contactors of the relay (that steers the Subwoofer one side and the Center speaker on the other side) are burnt and glued together......

[@waynegram8907]

If a transistors are two diodes, why doesn't a transistor rectify AC waveforms like a silicon diode would? I would think the transistor would rectify the AC waveform input on the base to collector and to the base to emitter would have two rectified waveform in opposite polarity. I'm not sure why a transistor doesn't rectify an AC waveform because its consider just two silicon diodes. Any reasons why transistors don't rectify the AC waveform applied on the base?

[@w2aew]

1. Bipolar transistors do have a pair of PN junctions, but they aren't really operating as two diodes. The base-emitter junction does operate like a diode and is forward biased when the transistor is ON. The base-collection junction is usually reverse biased un normal "linear" operation. It only gets forward biased with the transistor is saturated, such as in a switch application. 2. Bipolar transistors can, and do, rectify AC if the base-emitter junction is turned off during part of the AC cycle. This is exactly what happens in a Class B or Class C amplifier. In Class A, the transistor is bias so that the peaks of the AC aren't sufficient to overcome the forward bias of the base-emitter, so the transistor remains in the linear region.

[@waynegram8907]

@@w2aew If a diode doesn't have an DC bias voltage it will rectify an AC waveform but if you apply DC bias voltage until the AC waveform positive and negative cycles can pass through the Diode without getting clipped is the linear region of the diode. The difference between a diode and transistor is that when the AC waveform is passing through the diode is doesn't get amplify or increase in current gain. When an AC waveform passing through a transistor is increase the current and voltage of the AC signal. The transistor has something inside it beside a diode to make it increase the current and voltage of AC signals.

[@w2aew]

@@waynegram8907 Yes, of course. The base-emitter bias controls how much current flows from collector to emitter.

[@MrMac5150]

Teach us the proper way to test a Mosfet I heard they can be damaged easily if not tested correctly.

[@superdau]

If you just heard they can be damaged easily, you better look it up again. With the exception of them being more sensitive to ESD, you have to do really stupid stuff to kill them. Since they are voltage controlled devices they are way easier to test then the current controlled bipolars.

[@jsngallery]

my meter doesnt move at all

[@pirateman1966]

I bought a pack of assorted transistors from China. I am sure they are all fake. I wanted to find a way to test these against their datasheet. What parameters do I compare to the datasheet? It's not enough to compare Beta and Collector-emitter saturation voltage, that my component tester displays. What jig can I make to parameterize transistors with a scope +Sig gen ? I think a lot of people can use a clever technique. I would make a video and share it, but I don't know what I'm talking about.

[@ralph9987]

perfect, thanks 73 de vk4kdx

[@burneraccount8505]

Its so sad to hear "they dont use them anymore" right before saying how useful they are.......