#135 

He's too good for schools.

Thank you Josh - glad to hear that you have found my content useful. Did you check out the video index PDF file on the main channel page? (lower right corner of the banner graphic).

w2aew Thanks for pointing that out. Extremely handy having a “TV Guide” so I can what I want to watch next:). Very cool!

Indeed a very helpful lesson.

There are several factors in studying circuits. One resource I discovered that succeeds in merging these is the Gregs Electro Blog (google it if you're interested) definately the most useful info i've seen. Check out this awesome site.

Ya, I was already thinking about building a function generator with a 555 timer while watching the beginning :P

Yes and agree. Due all respects Hat tip for each moment of your teaching, Sir.

Thank you for putting that into words. w2aew and Dave from EEVBlog both really seem interested in TEACHING people and making otherwise super complicated EE concepts accessible. If these guys were professors in my school maybe I'd have gone the EE route instead of CS!

Very glad to hear that my videos have helped you. Congratulations on the Extra!

I've got two videos on ESR meters you can build. Here is a fun design that uses only 5 transistors: m.ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-3fiUZZlveS0.html And a design that I built many years ago: m.ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-bmYAgat-sOQ.html

Also take a look at the "5-transistor ESR meter" project.

100% agree, you beat me to it by 5 years !!!

Unfortunately there really isn't a bulletproof way to test for bad chips in-circuit. This is because other devices and circuitry in parallel with the capacitor under test can give you a false 'good' reading.

Hi. I know an instrument call Capacheck wich is possible to measure bad capacitors on board without remove it. It cost about 100 Euros. Best Regards

Jose Pico All instruments like this can be affected the same way - other devices on the board can mask a bad cap. In general - a bad ESR reading will usually be reliable, but a good ESR reading could still show up when testing a bad cap in-circuit, due to other circuit components.

Good luck with your studies! Be sure to share my channel with your fellow students, and your professors!

You probably dont care but does anybody know of a trick to get back into an instagram account? I was dumb forgot my login password. I appreciate any help you can give me.

@Cohen Legend instablaster =)

@Phillip Derek Thanks so much for your reply. I got to the site through google and Im trying it out now. Takes quite some time so I will reply here later when my account password hopefully is recovered.

@Phillip Derek it did the trick and I finally got access to my account again. I am so happy! Thanks so much you saved my ass :D

@Cohen Legend Happy to help :)

Electrolytic capacitors in electronic repairs are the most replaceable components and are bought in hundreds in every lab.Only from a small UPS and a dead 10 inch portable TV i replaced about 30 capacitors.Even those who measured as good are replaced also with the defect ones."Capacitor rejuvenation" is Bs.

Most of the DIY designs I've looked at use a test signal in the low hundreds of kHz and measure the AC voltage drop. I don't know what methods are used by commercial units.

The clip leads only reall affect things for the high frequency components. That's why you see some overshoot and ringing at the rising and falling edges. But the lower frequency components aren't really affected much at all. That's why we use just a few hundred kHz for the test frequency.

***** Explains why when trying the AC on the scope the noise was so bad I could not accurately measure. The leads I used were 2 feet in length . Put the cap under test directly on the BNC connector and problem solved. Will have to order one of the lead sets you have on my next Newark order. Cheers

Higher frequencies make it easier for the meter to show ESR for lower value capacitors.

Larger value capacitors generally require *lower* test frequencies (not higher). And, the *impedance* curves *will* vary with frequency - but that is not what ESR it! ESR=Equivalent_Series_Resistance. It should be relatively constant over the usable frequency range of the capacitors.

Oh, I see. Thanks for the help!

Thanks! How do you think I learned? By reading the Mims Notebooks as a kid many years ago...

+Vladimir Petrovic You can basically do the exact same thing as shown here - except replace the step-down transformer with a 1:1 audio transformer (commonly found inside old scrap telephones), and drive one side of the transformer with the function generator.

For low frequencies like audio, you rarely ever *need* the 50 ohm termination. The only time it is generally needed is when frequencies are high enough for the coaxial lines to be considered as transmission lines (when they're more than 0.1 wavelengths long). Audio is so low in frequency that this doesn't matter. However, since most function generators have a 50 ohm output impedance, they are usually designed to *expect* a 50 ohm load. If you have a high impedance load, then the voltage amplitude at the load will be double the set value because you're not getting the 50:50 voltage divider. This is not a big deal, just account for it. Some function generators allow you to set the load impedance. This doesn't really change anything about the signal being generator (or the output impedance of the generator), it just re-computes how the amplitude reading/setting is determined so that it matches what you see at your load.

No, no chart. I just start suspecting caps that show over a few ohms, and compare them to a known good one.

Requirements: An Oscilloscope And A Simple Signal Generator Setup: 1) Output of the generator; connect a BNC "tee" adapter. Run a 50-ohm BNC cable from the tee to the scope with a 50-ohm BNC terminator on the scope input. Terminator note: You can use a 50-ohm "pass-through" terminator on the scope end of the BNC cable. You should also be able to use, instead, another BNC "tee" on the scope input, with an "endcap" terminator on one side and the cable coming in on the other side of the tee. 2a) On the other side of the tee, connect a banana plug BNC connector with a set of DMM-type probes or alligator clips. 2b) On the other side of the tee, connect another BNC cable that has alligator clips on its other end. 3) Setup the signal generator to produce square waves at about 100-kHz with about 100mv peak-to-peak amplitude as seen on the attached scope, and no DC offset. Turn the scope's v/div to 5mv/div with time/div at 1 micro-sec, and AC coupling of the input. 4a) Shorting the probes together will display on the scope about one division high. It is basically a square wave with large narrow peaks at each leading edge. View the horizontal part's p-p amplitude. 4b) Try it with a decade resistor box in series with the probes. Should clearly see each one-ohm increase on the scope display with the probes shorted together as well as with the probes across a good electrolytic capacitor. Testing: - With the probes across a GOOD capacitor in-circuit there should be little, if any, change in the scope display as compared to when the probes were shorted (since, depending on the frequency, a capacitor should look more-or-less like a short circuit to AC. - Across a BAD capacitor, usually the display will be almost-totally off the screen. Some caps will look marginal, making the display go from about one div p-p up to about 3 to 5 divs; which probably corresponds with somewhere between 5-ohms and 20-ohms of ESR???). Comments: - Can test IN or OUT of circuit!!! -- In-circuit, low-amplitude is probably desirable; probably less than +/- 0.4v so the signal doesn't turn ON any semiconductor junctions. - Probably reliable for 10-uF 10v to at least 1000-uF 100v. - Adjusting the frequency for different capacitances might be helpful; especially if non-electrolytics are to be tested.

My only comments are that the 50 ohm termination isn't really needed since the capacitor shorts it out anyway. Just put the BNC tee and clip leads right at the scope to avoid transmission issues and reflections at the scope. Also, I never recommend in-circuit testing because other devices (including capacitors) in parallel will often affect the results.

Thanks. I learned a lot from the old "Engineers Notebook" series of books by Forrest Mims. The calculator uses an entry method called RPN (reverse polish notation). It is more efficient when computing complicated formulas. It's quite common in engineering circles (rarely used by casual calculator users).

@@w2aew Thanks and 73's -W1RMD