Resistor Question

Discussion in 'Datasheets, Manuals and Component Identification' started by H2814D, Sep 13, 2018.

  1. H2814D

    H2814D

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    Are there any other considerations I need to follow when choosing a .56 Ohm (560 mOhm) 2W wirewound resistor replacement for one that is open? There are no color bands on the resistor. It does have .56 Ohm, 481, and 2WJ imprinted on it. I am guessing the 2WJ is the wattage and the .56 Ohm is obviously the resistance. Does the 481 mean anything?

    Thanks in advance for your reply.
     

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    H2814D, Sep 13, 2018
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  2. H2814D

    dave9

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    That resistor doesn't look bad to me, are you sure it is the resistor itself rather than a bad solder joint or broken trace to it?

    No at that level it is just a current limiting resistor and you can pick any with similar specs, though if it was running hot and you can fit a 3W in its place, I'd do that.

    It may or may not help if you provided more detail about what this resistor is in, and what fault/evidence you have to cause you to decide it needs replaced.

    WHY wouldn't you do that? Is this a super secret death ray and nobody can know about it until all victims are dead? I really really don't understand how someone can be so lazy when wanting help from others. You literally want us to put in more time on this than you did, guessing and wondering and speculating, all because you couldn't be bothered to provide an appropriate level of info.

    It is very bad form to do this. How important it is to you to fix this should be measured in the effort you went to, to do so.
     
    Last edited: Sep 13, 2018
    dave9, Sep 13, 2018
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  3. H2814D

    H2814D

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    Haaaa....thanks for your reply, dave9. :) It shows open with zero resistance. That is why I have to replace it and how I know it is bad. I wish I was as good as you and was able to tell if an electronic component was good or bad just by looking at a photo. I mean, that is a skill to have for sure. :)

    It is simply a part of a dual voltage DC output power supply I am trying to fix. That was the first component I have found that is bad so far. Nothing top secret or anything. And I wasn't being lazy. I thought my question covered everything you would have needed to know about what I was asking about.

    Believe me, I know what a valuable resource you guys are and have been to me and most everyone else who comes here for information, so I try to be careful with my offensive and lazy ways. :)

    By the way, I think your second paragraph answered my question adequately. So thank you.
     
    H2814D, Sep 13, 2018
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  4. H2814D

    hevans1944 Hop - AC8NS

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    Open should show infinite, not zero, resistance. Most digital meters will display OL to indicate an open circuit when trying to measure resistance greater than their range capability.

    OTOH, if the value is really 0.56 ohms, that's pretty close to being effectively zero ohms as far as most multimeter ohms functions are concerned. You must take into account the probe and connecting lead resistance when making such a measurement. Make sure you "zero" the ohms function by shorting the probes together before trying to measure the value of the 0.56 ohm resistor. Whatever value the meter indicates with the probes shorted together must then be subtracted from the value read when measuring the 0.56 ohm resistor. This is similar to the tare weight you subtract when measuring weight on scale. Some meters have a button you can press to remove the small resistance presented by the probes and the test leads, thus ensuring that any resistance measurement begins with zero ohms when the probes are shorted together.
     
    hevans1944, Sep 14, 2018
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  5. H2814D

    davenn Moderator

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    Maybe it isn't if you misread your meter...…...


    In the words of the song by Meatloaf …. " You took the words right out of my mouth"


    Dave
     
    davenn, Sep 14, 2018
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  6. H2814D

    HellasTechn

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    I agree.
    Also i think that you may be able to get a better reading with an analog Multimeter.
     
    HellasTechn, Sep 14, 2018
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  7. H2814D

    hevans1944 Hop - AC8NS

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    I agree that analog meters are more useful in making low-resistance measurements. I love my little Triplett Model 310 pocket-sized multimeters, of which I own two. One has an external clamp-on AC ammeter that attaches to the top of the meter case. The other has the clamp-on fitting but is lacks the ground return for the clamp-on current transformer. The meter faces are marked differently too: the ammeter function on the clamp-on meter is used on what is normally the 3V AC range of the other meter, but is marked AMPS on the meter. You can't see that in the low-quality web-cam picture I took using this HP Pavilion g6 laptop:

    upload_2018-9-14_10-37-41.jpeg

    Anyhoo, analog meters are great when you are looking for trends rather than exact measurements. Even the small meter on the hand-held Triplett can be easily "read" from across the room to get an idea of which end of the scale the meter needle is on. I think someone should replace the analog D'Arsonval movement with a high-resolution LCD back-lit display, featuring the same analog meter capability but with a small numerical readout under the analog scale. Best of both worlds that way. My B&K Precision multimeter does have an "analog" display bar at the bottom of the large digital readout, but it just doesn't "feel" or look the same as my Triplett meters.
     
    hevans1944, Sep 14, 2018
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  8. H2814D

    H2814D

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    Thanks guys, for the replies and information. When I used the term "open" I was referring to the passing of any current through the resistor. I did that part of the check check using the continuity (diode) setting on my multimeter. The display did not change from the one being displayed before connecting the probes to the resistor. Just to be sure there should have been a reading, I took another resistor (1/4 watt 560 mOhm) and measured it. When doing that, I had both resistance and continuity. My meter actually provided an accurate Ohm reading on the resistor using the diode/continuity setting on the meter.

    Am I missing something else, or should I consider the resistor to still be bad? I've got it on order anyway, and will check the new one the same way, but now you guys have me doubting my initial evaluation.

    By the way, have any of you seen that computer video prank where you stare intently at the computer screen, and then you have to concentrate on moving a cursor through a very thin maze, to end up at the other end and then that scary face pops up and screams at you? :)
     
    H2814D, Sep 14, 2018
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  9. H2814D

    Bluejets

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    Aren't these a metal oxide resistor (flameproof)...??

    Some are designed to act like a fuse on the mains input area.

    For future note, I wouldn't use diode test range to get resistance values.
     
    Bluejets, Sep 15, 2018
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  10. H2814D

    H2814D

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    Actually, I just came back here to report that I am not able to duplicate the diode setting-resistance value claim that I made before. I only get voltage through the resistor, and not capacitance. And I only used the diode setting to confirm continuity through the resistor, not to obtain the impedance.

    I do believe this resistor is just that, a secondary over-current check, because it is attached to the first power transistor and that transistor has also failed. So that would explain the very low impedance (.56 Ohm) used at that resistor location, right Bluejets?

    So in my first posting above, if this is resistor is acting as a fuse (backup), because the board actually has another wire/glass fuse at the mains, are there any other considerations I need to adhere to when replacing this resistor? You mentioned metal oxide and flameproof and that is what I have ordered.

    Thanks again for your replies.
     
    Last edited: Sep 15, 2018
    H2814D, Sep 15, 2018
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  11. H2814D

    Bluejets

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    There are instances where transistors use resistors such as this for ballast resistor. i.e. where more than one transistor is used in the output to share the current.
    Depends what you have .

    As far as the multimeter, use normal resistance range for resistors and diode test for diodes.
    If you need to measure low values of resistance, you can knock yourself up a relatively simple 4 wire current injector (LM317) and use the multimeter to measure the voltage drop.
    In this instance the voltage drop reading is the resistance value because of the formulas involved.

    http://electronics-diy.com/electronic_schematic.php?id=951
    Can be useful for other things as well, e.g. motor winding measurements.
     
    Last edited: Sep 15, 2018
    Bluejets, Sep 15, 2018
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  12. H2814D

    H2814D

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    Thank you again, Bluejets. I do use the resistance setting for resistors and the diode setting for diodes. The diode setting on my multimeter is also the continuity setting. I just have to push a button to get a tone for conductivity.

    Reading voltage drop is a bit past my level when it comes to electronics, so you kind of lost me there. But, because it is something I don't know about, I will read about it shortly. This stuff is simply a more of a challenge than anything else. Haaa...and with my postings, apparently challenging the patience of you guys.

    Just for fun and as a project, I ordered and assembled a DSO138 Oscilloscope (with many SMD components using hot air and solder paste) and have ordered a GM328 for assembly as well. Cheap devices, and toys compared to the equipment available, but apparently both have been well reviewed. Now I just have to learn how to use them. :)
     
    H2814D, Sep 15, 2018
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  13. H2814D

    Bluejets

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    Flood here back in 2013 took all my gear and slowly getting back up there.
    Bought a little DSO150 just to get by until I get a decent scope once again.
    It's ....mmm...ok but....... if you get my drift.
     
    Bluejets, Sep 15, 2018
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  14. H2814D

    undesaz

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    Better to use digital multi-meter for accurate measurement.
     
    undesaz, Sep 15, 2018
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  15. H2814D

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Actually, for very low resistances it's best to use the correct instrument. That instrument is not your typical multimeter (unless it has a 4 wire ohms measurement mode).

    Whether it's digital or analog means far less.

    Adjustments to zero the meter were far more common in analog meters. This is actually an advantage of the older (and simpler) instruments in this case.

    Interesting enough, an ESR meter is also a viable option.
     
    (*steve*), Sep 15, 2018
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  16. H2814D

    hevans1944 Hop - AC8NS

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    Accuracy and resolution (number of digits displayed on digital multimeter) are not necessarily related. My B&K Precision Model 2890A Multidisplay Multimeter displays from 00000 to 49999 before it goes into OL indication on the display, so it has a resolution of one part in about fifty thousand or about twenty parts per million. The resolution for resistance measurement on the 500 ohm range is 0.01 ohms, but the accuracy of resistance measurements is "only" ±(0.8% of reading + 5 digits)... this is a long way from 20 ppm!

    As @(*steve*) said in post #15 above, "for very low resistances it's best to use the correct instrument." I use my B&K multimeter to routinely measure very low resistances, but I have to "zero" it before each measurement. The minuscule contact resistance of the shielded banana plugs changes with the slightest movement of the leads, which can introduce several milliohms of error in the resistance reading unless the initial (already low) connection resistance is nulled to zero by pressing a button on the meter.

    A better way to measure very small resistances is to introduce a constant current and measure the voltage drop across the resistance to be measured. Most digital multimeters work this way. The four-wire resistance measurement technique is a variation of this procedure with two wires providing the test current and a separate pair of wires sensing (without appreciable loading) the voltage drop across the resistance being measured.

    Wheatstone bridges, with analog null meters to detect bridge balance, were once the "gold standard" for measuring unknown resistances, but by and large, not very portable, and they require considerable skill and knowledge of potential "gotchas" to use successfully. The same requirements for skill and knowledge apply to more modern resistance measuring tools: you have to know what you are doing and why you are doing it to obtain accurate and meaningful measurements.
     
    hevans1944, Sep 16, 2018
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  17. H2814D

    H2814D

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    Just so you know, I have received replacement .56 Ohm resistors. My meter will display .6 Ohm and drop to .5 Ohm, back and forth. So I am going to conclude my meter is at least able to measure a resistor of less than 1 Ohm. I have an analog meter somewhere. The first one I ever bought and it was probably 40 years ago. I haven't used it in so long I don't remember where I put it. I'll have to find it, so I can see if it will read the correct (.56) resistance.

    Anyway...thanks again for the info everyone.
     
    H2814D, Sep 19, 2018 at 4:19 AM
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  18. H2814D

    hevans1944 Hop - AC8NS

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    Just so you know: voltage is defined as the electrical potential measured between two points. So-called voltage drop occurs across particular components in an electrical circuit when the current in the circuit is impeded (or resisted) by components that exhibit resistance (resistors), reactance (capacitors and inductors), or both. If both resistance and reactance are present, the combination is a complex number called impedance. In a series circuit connected to a voltage source, the sum of the voltage drops across all the components in the series circuit must equal the voltage supplied by the voltage source.

    This may be more than you need to know right now. Good luck repairing your power supply.
     
    hevans1944, Sep 19, 2018 at 4:07 PM
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  19. H2814D

    H2814D

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    Thank you, hevans1944. I actually did read about voltage drop and found it wasn't as intimidating as it originally sounded. Your last post summarized my understanding quite well. As far as being "more than you (I) need to know..." let's just say there is quite a bit that I do need to know and finding it out is better than not.
     
    H2814D, Sep 19, 2018 at 7:05 PM
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  20. H2814D

    hevans1944 Hop - AC8NS

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    I know the feeling. Back in 1967 I was completing a four-year term of enlistment as an Armament and Electronics (A&E) maintenance mechanic with the USAF. The previous year I had studied and passed an exam (code at 5 wpm plus theory multiple-guess exam) to qualify for a Novice Class Amateur Radio Operator's License, call sign KN8UTJ.

    So, on my discharge from active duty date in May 1967, I had almost a year of experience operating a small CW transmitter I had built from scratch, pounding on a straight key to send Morse code at (eventually) speeds of up to 20 wpm, and listening for Morse code contacts on the Novice segment of the 80m amateur radio band using a kit-built SB-300 receiver purchased from Heathkit. I knew I was ready to take the FCC test for either Technician or General class license, which at that time was administered by FCC examiners in Columbus, OH.

    Long story shorter: I got out, found a decent job, went back to school, found a wife, fathered and raised four kids, graduated from college and spent the next thirty-something years working for defense contractors. Never did make it to Columbus to take the amateur radio exams. Flash-forward to 2013. Nearing the end of my engineering career, I decided to try for an amateur radio license again. By this time the Morse code requirement had been dropped by the FCC, so my rusty CW skills were irrelevant. There was no need to travel to a Federal office building to be examined because the FCC had allowed the establishment of a volunteer network of Volunteer Examiners who were licensed Amateur Radio Operators, General or Extra Class.


    So, being a Dayton, Ohio, resident at the time, I attended a meeting of the Dayton Amateur Radio Association (DARA) and joined their club. DARA sponsors the annual Hamvention and administers no-fee amateur radio license examinations throughout the year. So, in March 2013 I attended one of their exam sessions and in succession passed exams for Technician, General and Extra Class licenses, receiving my Extra Class license from the FCC on April 1, 2013, call sign AC8NS. Previous to sitting for the examinations I had purchased on-line study materials from HamTestOnline.com. Although it had been forty-six years since the last time I had held an amateur radio license and operated "on the air," most of the technical details came back to me, and new technical details that had occurred in the interim were easily learned. All that was lacking was experience in current amateur radio operating procedures. I am slowly learning about that too.

    So dust off that old analog voltmeter and begin to enjoy the electronics hobby. Whatever you learned forty years ago will eventually come back to you. Some sage advise I got from an engineer at Oak Ridge National Laboratory (before he retired): STAY OUT OF THE HIGH VOLTAGE!

    Hop
     
    hevans1944, Sep 20, 2018 at 6:01 PM
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