#49: Simple Component Tester using Oscilloscope - Octopus Curve Tracer 

I was introduced to trace analysis 25+ years ago when I worked at a component-level repair facility. I built my own octopus, bought an O'scope and got busy fixing my own things! The world is more interesting when you learn something every day!

It may please you to know that, ten years on, you still have some interested viewers. Thanks for concisely demonstrating and explaining this piece of test equipment . Seeing it operate is both fun and illuminating!

I’m embarrassed to say as an engineer I never worked with the xy mode on my oscilloscope. You now have given me a whole new set of test tools with my 465 thank you so much!

The amount of practical and extensible knowledge provided in this video exceeds that of the first half of most introductory electronics textbooks. I'm consistently impressed with your videos and always look forward to the next.

I first became with an octpus aboujt 35 years ago. It was in a U.S. Naval publication published for ET's. Very helpful little tester.Thanks for making the video.

Back in the early 1970s, QST published a schematic for an octopus and I put one together, mainly because I had a cast-off all-tube, purple trace oscilloscope that must have weighed about 100# (my dad picked it up when his university chucked it). Anyway, I was about 14 years old, and I thought the octopus was particularly cool because you could test parts in-circuit. One day my ham transceiver (Henry Radio Tempo One) died. The power supply was blowing fuses immediately. So I decided to look around with the octopus, and rapidly found that one of the discrete silicon rectifiers in the full-wave bridge in the 500v (IIRC) supply was blown (I do not recall whether it had failed open or shorted). In any event, I was able to replace that rectifier and got many more years of fun out that transceiver. It's nice to see that these tools are still in use!

Thank you. Used this type of device when learning basic electronics in the military in the 70s. Glad to find it again.

I always learn from your presentations. Either new information for me or a different view of something I already know (or think I know!). Thank you.

Thanks a lot for this upload. Added to my favourites, very informative. Also your way to reduce the circuit to its bare essentials. Makes it simple to construct.

Excellent video, crystal clear explanation of how a curve tracer functions.

That is so cool. Now I want to rig up a tester circuit and check out a bunch of mystery components laying around. Love your videos!

Brilliant video. It explains the theory so clearly. Our component tester, the PinPoint II-R, uses this circuit to great effect, but I've never fully understood just 'HOW' it did it.

Great descriptions as always Allan. I was admiring your 465B, in terms of its cosmetic appearance. I would hazard a guess that the 465 series of scopes must have outsold any other model. I have worked around the world, & any lab I had access to always had at least one, & often a number of 465's. Every commercial radio shop in North America had at least one. I also have a 475 that I purchased in a pawn shop, inoperative. The owner asked me for an offer, & I told him that I would have to take the scope apart & have a look before I would make an offer. He looked at me & said " Twenty-five dollars as is. !" I pretended to consider his price , & said " OK, I will take a chance & buy it " He handed me the scope & I handed him the cash, & he said " Hold on Q" He searched through a couple of drawers & came up with a box that had 5 Tek probes, that had never been out of their packaging. The cheapest one of them was over $200. He said " There are five of those like the ones plugged into the scope...give me $5 each for them as a package deal. The best deal I ever made Allan ! I traded three of the probes to an engineer friend & kept two, because I could use the. The 465B & the 475 & the probes are on my service bench to this day. I swear the militaries of the world all had those God awful looking military cased 465s.

BTW, meant to add that your explanation is excellent.

This is the best, if I did not hear it from you, I would not have known about it, I think some of the old electronic teachers, have about 1 percent of your knowledge. Good Job.

Thank for this video. Explains things in a clear and concise manner!

Been watching your tutorials, great info and thanks... Well done and very articulate.

I built and used this test circuit for many years while working at WSMR when we still repaired equipment at the component level - as you mention above it is best used to make comparative measurements from known good to a circuit under test. I have fixed many problems using this circuit - thanks for posting it.

I was introduced to the component tester, while I was serving in the AF, in the early 70’s and this toy was old then. In the hands of an experienced technician, you could go through a bunch of transistor logic computer boards quick, this includes analog boards. It just takes about a few dozen boards to get the experience you will need for the transistor logic. The analog board where somewhat simpler, due to the fact the failures were sometimes more pronounced, but still had their quirks to work out. The short cut, for analog boards, was to compare a good working board with a bad one, when you had that luxury. Still have mine, that I used in my early days of board repairs. Update: Had to replace the BNC connectors as one was broken and had to get two to mach.

Back in my day this was a pretty high dollar piece of test gear called a huntron. I couldn't afford one so I designed and built my own much like you have represented here. Absolutely great video.

this is essentially a Huntron! Amazing video, thank you very much

Yes my scope has a component tester and I used to use it as a double check that the component was faulty. It was very interesting back then. Thank you for the video and explanation.

every bench at my place of work has this setup. mostly new equipment with these older scopes setup as tracers...very useful! tempted to build one myself for home.

Thanks alot!! When I saw this I remembered I had one in the garage that I made 35 years ago. Still viable today.

Mindblowing. I didn't know of this, wonderful!

Great tutorial, useful information excellently presented. Thanks.

Very nice demonstration! I built one of these in a small box using a couple of BNC's and two pairs of binding posts, and I included a couple of switches to select a current sensing resistor (for 1.0 or 0.1 mA/V display), and an attenuation factor (x1 or x10) for the voltage output. Driving it with a function generator lets you see frequency effects, which is useful. On my 2246 I have to invert the Y channel to get positive current going "up".

Thanks for a very clear intelligently-presented video. :)

Heath was a great self learning structure and I studied several electronic computer courses. thanks. 5 stars.

Tank you, Mr. n'kay! This was very usefull and very good explained.

I used to use a Huntron Tracker, which was commercially popular for trouble shooting in circuit. Worked great. Also built one in to my old B&K scope decades ago, that I grafted another CRT in to, after buying both for ten bucks each. Today, the only scope I know that has that function built right in, is the Hameg entry level HMO series, along with it's standard MSO capability. It's a great tool on any scope for component testing!

We used to use an Octopus many years ago when testing computer boards. We had a unit (later a Huntron) which had a ground and two probes and a circuit which switched between the two probes. Then the ground was connected to both a good board and a bad board at the same spot, usually the ground connection and then the two probes were put onto a test place on each bpoard and the patterns compared is the Octopus switched between the two. This was a very useful test tool.

Thank you for all these great videos.

Another great video, Alan!

Absolutely love this video looks really useful, off down to the lab later to try it out. Thank You

Excellent video with very informative content.

Great tutorial: I did BE+E school in the navy followed by radar”A” school but never did we get into the octopus circuit. I had a small stereo and CD player repair business to make a few dollars after getting out and ran into a former professor from Georgia Tech who briefly mentioned Octopus circuit. Interpreting the “L” from standpoint of voltage and current is straightforward. The oval for the capacitor is unique. I get a kick out of people with a batchelors degree making 50k to 60k while I made 120k at the phone company with an electronics education. LOL

You sir are amazing guy , so much information and at the same time so beautifuly explained

@w2aew Still relevant, instructive and enjoyable ! Thanks for making and sharing :) Best regards

excellent tutorial on how to use your oscilloscope to test components! now to make an octopus circuit!

I first came across this little jewel back in the Navy in the '70's. Was found in one of our technical issues. I built one and used it in the shop.

Great video. I have been using my octopus for a few years. I love it and use it a lot since most of the things I have to fix are broken due to a component failure. I work on cars and most of the time it’s a bad component or bad solder joint that has happened due to thousands of miles worth of vibration on it. I actually use the octopus more than use my scope in regular mode.

Thanks for sharing your knowledge.

I love watching your Uber informative video. I know some are old but definitely useful. I love your super clean vintage tek scopes. I a couple of nice ones. But yours look new.

NOW I understand what it is that my bench tech here uses at the shop to check components out in cct Nice video awesome

Thank you! Invaluable video!

Thanks a lot, always learning something new

I recently saw my first transistor used as a zener in the VFO of a Heathkit HW-101. Confused me for quite a while. Good circuit, good video

My experience with this tool was with Huntron ProTrack I. Loved it, I was a master at finding bad components. Now I'm using a usb o-scope and a scanner. Same thing but with far less capability. Still does the basics though, all you need on average is the low, med1 and med2. But changing the variables is pretty fun though!

Excellent tutorial!

Just great! It was very helpful. Thank you very much!

Well, I know what my weekend project's going to be. It will be a good use for my recently-acquired function gen :) Thanks!

Very usefull explanation, Thanks a 1000 times :)

Back in the late 60'sI built about the same thing except with a transistor as a fixed current limiter and a voltage of about 300V. I did a lot of amplifier repair and bought the cheapest low voltage TO-220 transistors. The difference between transistors in a number series was that they were selected. You can't make transistors with particular voltage breakdown. Then I just selected out the higher voltage ones for amplifiers. Lower voltage ones were used in car radios. 95% of 30V rated transistors were well over 120V. On rare occasions I would get one with a squirrely point on the curve but still worked. That went to the dust bin.

Thank you for an interesting video.

This is a great tool to test homebrew crystal radio detectors. Trying now to build an old portable tv into a curve tracer using this type of circuit as the interface.

Good - very much useful information!!!

Loved the demonstration. Can't wait to try it out myself. I was looking for a curve tracer like I used to use at my old job. This seems much easier to deal with and not too difficult to build. Very cool.

Another excellent video that makes me look at my scope in a new way! Thanks and keep up the good work!

great video and very useful

Thankyou. very informative

thanks for introducing octopuss

Hi Allan, Another Excellent video and TNX OM.. There was a commercial version of this device years ago called the Huntron. and it was a BIG dollar item. Seems like over $500 in the late 70's or early 80's. It may have had a few voltage sets but still a simple overpriced item but helpful. I have a Tek 576 curve tracer in my lab but use this simple tool for a quick check for leaky xsistors/diodes and use it often. It is handy to have a good example for go no go comparisons. 73, Glenn WA4AOS

Love your Videos :)

Very helpful. thank you!

I've always wondered how they worked thanks.

The name octopus likely comes from the looks of common devices. A box (=head) with 5 leads coming all out from one sides (2 bnc cables to the scope, 2 test leads, 1 power cable, or when the power cable is at the back, a "nose" in the center, which is a trim pot/rotary switch to select the voltage).

I first encountered this circuit in Popular Electronics, 8/75. According to the article, this first appeared in a John Rider book in 1935. The name, Octopus, came from folks in the Navy. If you count the number of connections, including a grounded Line cord, you get 8 leads.

Enjoyed the X-Y tutorial !! Gary Grove

Thank You so much for video!!!

We dedicated a OS-8 oscilloscope as a dedicated Octopus. US Navy early 70’s

great video my friend

exelent as allways!

What a wealth of info for a beginner like me! That's really encouraging, thanks a lot!

Thanks! Very useful if you now have a digital scope and you miss the comp tester from the analog one..

Thanks, Ron

very GOOD VIDEO!!!!

Nice info, thanks :)

Thanks so much for the quick reply, and thanks for the awesome videos... much appreciated!!!

Thanks for sharing. Works very nice on every component except coils. Anyway, I just thought I gave it a try and it is a handy tool to have. I personally would not rely on such an instrument because it doesn't give number readings and such so it is a very limited tool from my point of view. Keep up the good work. :)

I use them since education.....around 40 years. a pretty good and fast method to work thru a unknown board. With time you can tell it is a zener 12v or this caoacitor is leaking and so on. I modified myo old hameg this way with swichable voltage and current (with limmitations ). For fast repair it is best for me.... i have a modern component tester .... but it is mostly not neccasary to desolder comonents with the oold method so i stick on that. Sorry for grammatics and so on.....i am not a natural english speaker ;) Best regards from Bavaria.

Lovely to see this very good tutorial

This is very useful! Thanks for sharing!

Thank you!

Thank You!

Very good Alan, using the equipment you have for many uses.and also learning the Scope can be utilize as many tests performed, a little closer look at the results. Thanks for the wisdom, I have a swell head now !!! I just left Mr Carlsons Lab lol now into more info lol Just great to have such good friends. 73's Alan Look at those hits !!

subscribe? absolutely! your videos are interesting, well produced, and straight to the point. congradulations! I am newly licensed amateur (ag7by) and feel lucky to have found your channel. I am slowly gathering test equiptment and hope to build radio related projects; this "octopus curve tracer", which I had never heard of, should be very useful. thanks for the work you put into these videos. '73

Hi ! Im so glad to see all your videos , actually im working on automotive electronics , i want to see you may be explaining some things about it, structure, automotive components , caracteristics . Just in general. Hi from Mexico !

Thank you so much

useful video ,good.

Nice video. I learned a lot on this one. Thanks

Thank you for explaining this to us. I wonder what limitations this technique has when testing components in circuit.

I used a Huntron component tester at the company where I worked. It wasn’t cheap. It could do very high frequencies. My professor at community college showed me how to make an octopus. It even had a current limiting potentiometer. I built it and put it in an old project box from the C-band satellite positioner we got rid of decades ago. This octopus is over 30 years old. I used it today to troubleshoot the rail switchers on an Arc 1000.1. It sniffed out bad A06 transistors immediately.

QUESTIONS - What a wonderful video...and I just now FOUND it! Finally I understand how these work. If you see this... I have a couple of questions..... 1) will this test RF power transistors as well? Can you depend on this to evaluate a good vs bad part? 2) IN a discussion I just saw today (on the merits of doing COMPLETE Electrolytic cap swapouts in radios!)... ONE user said that they use an octopus tester on the electrolytic caps..... Circle? It is good..keep it. Flat line? bad! Replace it. That sounds simple....BUT ... is an octopus tester suitable for "in circuit" tests like that? AND....when using it "in circuit" will the display on the individual component be "reliable" OR can the surrounding components "throw off" the display form.... so that you could not detect a "failed part" or to me... more importantly.... a MARGINAL part? I would want to be sure that I can detect a "flaky part" that could go at any time (IF that is possible! But I would not want the "in circuit" use to affect my ability to test! I am just curious as to your opinions (and anyone else who may care to chime in!) on these questions. Thank you so much for this video!!!!!

Thank a lot for your help. If I pull channel 1 knob it multiply by 10. It works for diode, zener, capacitor NPN, but: - good resistor give a vertical line - good electrolitic capacitor give a vertical line - the zener like base emitter junction does not show the little hook Has I dont have shorted or open component I cant say fo theese.

I only wish it was that simple. Your help was greatly appreciated. This is just an old analog scope I had and very rarely used. I found that if I set the Vert mode to Ch. 2 the CRT goes black. Channel one works fine. When it is in X-Y mode it appears to be normal but I am short channel 2 or “X”. Again, thanks and keep sending the great videos. .

Nice! I've used a "curve tracer" for going on 30 years. Also great for in-circuit testing on un-powered circuits. With a little getting used to, can be a great go, no - go tester for troubleshooting.

Thank you for another educational video!

Yes indeed! I had a loop ( to insert a mult. probe) in the wire from resistor to ground. I solder it for the current to go trought and everything is ok :o) I dont know where you will store all my thanks :o) JP

A capacitor will an oval. If it has ESR it will tilt the oval. Also you can spot noisy pots, as you move the control the trace will rotate vert horiz and back as you move the pot. If the pot is noisy the line will show noise spikes