DIY Cables - What's the Best Way To Test Them?

Discussion in 'Archived Threads 2001-2004' started by Scott-C, Apr 7, 2002.

  1. Scott-C

    Scott-C Supporting Actor

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    After reading about a way to make DIY cables here, and discussing it with some other HTF'ers, I've decided I'm going to invest the $$$ in the tools and start making my own cables. Since separates are in my near future, I will be able to recoup the tool investment pretty quickly.
    What is the best instrument-based way to test a DIY cable before I put it into use? One HTF member uses an ohm-meter to check the cable before putting it in his system. I'm just wondering if there are other ways to test the cables so that I can have peace-of-mind prior to using it.
    I was looking on Markertek's site and they seem to have a lot of diagnostic instruments, but I'm unsure if they will do the trick for me.
    Thanks!
     
  2. Peter Johnson

    Peter Johnson Stunt Coordinator

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    IC's: You should get a short circuit from hot to hot pins, and ground to ground (outer bit), which will measure on a multimeter as almost zero ohms.
    It should be an open circuit from ground to hot. Either no reading, or a VERY high one...depending on your MM.
    Speaker cables..a bit harder to stuff up [​IMG]
     
  3. JimN

    JimN Stunt Coordinator

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  4. Scott-C

    Scott-C Supporting Actor

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    Peter,
    Thanks for responding. Forgive my ignorance, but much of what you said went right over my head. Can you explain what you're talking about it layman's terms?
    I think I might need a little more specific info so I understand it better. What diagnostic equipment do I need to buy? (multimeter, ohmmeter, etc.) and exactly what do I do with it?
    :b Sorry, this is not my area of expertise!
     
  5. Brandon B

    Brandon B Second Unit

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    Basically, any standard meter that will measure resistance and an open or closed circuit.

    You want to measure the to make sure the center pins at each end of the cable have 0 resistance between them (or nearly so), or continuity, and likewise the ground connectors at the 2 ends. You also want to check to make sure you do NOT have continuity between the outer part of the connector and the center pin (very high to infinite resistance is what you should see).

    If there is a short between the ground and signal leads (outer sleeve and center pin) you may damage your system. If there is no connectioon between the pins at the 2 ends or between the grounds at the 2 ends, it just won't work.

    As to whether your new cable is better, your ears decide that.

    BB
     
  6. Scott-C

    Scott-C Supporting Actor

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    Will a basic ohm meter do the trick here? They seem pretty inexpensive.
     
  7. Brian Bunge

    Brian Bunge Producer

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    Scott,

    Yes that will work. I like the ohm meters that have a "continuity" setting. They usually have an audible beep if there is continuity. No beep, no continuity.

    Brian
     
  8. Scott-C

    Scott-C Supporting Actor

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    Thanks Brian! Can you recommend one in particular, or provide a link to one? I've found a few ohm meters but I don't recall reading about a "continuity" setting, and that sounds nice.
    I just found a digital multimeter at Sears.com for $24.95 that looks cool, but it's probably overkill since it measures volts, diodes, etc. And, I didn't read anything about continuity.
     
  9. Brian Bunge

    Brian Bunge Producer

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    Scott,
    You might want to try this from Parts Express. It doesn't state that it has an audible continuity tester, but I bought their $88 model and it has it although it doesn't specify it either. With mine when you set it for the lowest ohm rating you automatically get the audible beep.
    You might want to call PE's Tech Support as see if they can answer that question for you.
    Brian
     
  10. Scott-C

    Scott-C Supporting Actor

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    Brian,
    I also found this one at Parts Express and it mentions a continuity beeper.
    Not being the most electrically inclined person, let me ask this: if I buy a multimeter without a continuity beeper, how exactly does one test continuity? What do you do to test it, and what indicator tells you about continuity?
    Also, I noticed most multimeters seem to offer "resistance ranges". What does this mean?
    Something else I just noticed. Some of these multimeters have resistance ranges that start at 300 ohms. Wouldn't want one that can measure at 75 ohms?
     
  11. Brian Bunge

    Brian Bunge Producer

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    Scott,

    That looks fine too. The test methods that others have mentioned above are basically continuity tests. Touch your positive and negative leads to both center pins of the RCA's. If there is continuity you will get a beep. Then do the same with the outer sleeves. Then touch the outer sleeve with one lead and the center with the other. There should be no continuity and therefore no beep. If it does beep, that's bad!

    The choose the range based on the resistance you want to test. Say you have some 500 ohm resistors that you want to verify are truly 500 ohms. You'd select the next range up (say 1K ohm) to test them. Some meters, like my Radio Shack meter, is autoranging.

    EDIT: The 300 ohm range is for 300 and below. I'm assuming you're talking about measuring for 75 ohm impedance? Forget about that. Impedance is frequency dependant, so it will change based on frequency. An ohm meter is to measure DC resistance. All you are concerned with for interconnects is continuity.

    Brian
     
  12. David A. Frattaroli

    David A. Frattaroli Stunt Coordinator

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    I use a Radio Shack Mutlimeter and test for continuity. It beeps for confirmation. Then, I usually dump the cable into my old office system and use it as a guinea pig before it goes into the HT.
     
  13. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    As Brian pointed out, you cannot measure impedance with an ohmmeter. You would need an expensive piece of gear for that. Checking for opens and shorts will catch nearly all problems. First component cable I built had 0 continuity from male pin to male pin on one of the inner cables. I traced it back to a poor crimp on the Canare inner pin (I hadn't calibrated the crimp handle pressure :b).
     
  14. jeff lam

    jeff lam Screenwriter

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    Most MM's have continuity testing built in. Even my cheap $15 Radio Shack pocket DMM that I got for my birthday when I was 15 has an audible beep to test continuity. The battery just died last year[​IMG]
    That little thing has served me very well throughout many years and countless car audio instalations for my friends in high school. Time to upgrade to a real one though, I just haven't needed one lately.
     
  15. Brian Bunge

    Brian Bunge Producer

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    I think this meter from Parts Express is an excellent unit if you also want the ability to test inductance as well. Mine has come in quite handy.
    Brian
     
  16. Scott-C

    Scott-C Supporting Actor

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    Excellent information in this post, guys. Now I feel more comfortable knowing that pretty much any DMM I buy will be ok.
    If for some reason I wind up with a DMM that does not beep to indicate continuity, what should the indicator say to confirm the continuity (I touch one lead to the RCA center pin on one end of the cable, and touch the other lead to the RCA center pin on the other end...at this point what should I be looking for)? Sorry for all these questions guys - as I said this is not my bag so I'm trying to learn as much as possible from all of you since you've been down this road.
    Brian, thanks for that explanation on how to test; it made sense except for the part about touching the "outer sleeve" of the cable - what is that, exactly? I envision a coaxial cable having a center conductor, a shield, and a jacket. Which one is the "outer sleeve" - the jacket? I can't imagine you'd get any reading by touching it since it's shielded...would you?
    I should have paid a whole lot more attention when they taught this stuff in high school! :b
     
  17. Bob-N

    Bob-N Supporting Actor

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    Hey, I can answer these questions.

    Regarding the continuity, what you should set your DMM to is to measure resistance. That is normally signified by "ohms" or the greek letter omega (upside down horseshoe). Touching each male conductor (same goes for outer sleeve) on each end, you should measure close to 0 ohms.

    I think what the guys here are talking about when referring to the outer sleeve is the outer conductor or the "shield" as you call it. That goes for both RCA and coax F type connectors. It's the part of the connector that you use to pull on or screw on to connect and remove your cable from.

    I hope this helps.

    Bob
     
  18. Scott-C

    Scott-C Supporting Actor

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    Thanks Bob. [​IMG]
     
  19. Scott-C

    Scott-C Supporting Actor

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    Having received my cable and accessories, and tools, I attempted to make a sample cable today for practice. Overall I was pleased with the process but want to double-check to make sure the cable is technically OK, before I put it in system. Here is what I did as far as testing:
    1. Before connecting the RCA plugs, I touched the red and black leads to the center crimp pins (the small pin that you connect to the cable) and measured for resistance. Is this test legitimate/necessary?
    2. Touched the red and black leads to the center RCA pins on the cable - red to one RCA pin, black to the other RCA pin (on the other end of the cable). Measured resistance between 0.2 and 0.5 ohms.
    3. Touched the red and black leads to the outer crimp sleeves (the metal tube that gets pushed up against the RCA jack and crimped). Measured resistance between 0.2 and 0.5 ohms. Is this test necessary?
    4. Touched red and black leads to the center RCA pin and outer RCA "barrel" on one end of the cable, then repeated for the other end of the cable. Got no reading (i.e. no continuity).
    Some questions:
    1. What is an acceptable reading for continuity? Put another way, are my resistance readings OK or should I be shooting for "0 ohms"? My multimeter does not "beep" for continuity.
    2. I couldn't really get the multimeter to register a static reading - the reading "jumped around" a little bit, generally between a range of numbers. Is this normal?
    3. Are all my tests correct? Are there other tests I should do?
    4. What is the correct crimp handle pressure? The default setting on the crimp handle seemed too light, so I unscrewed the screw, and then used a pliers (sp?) to turn the dial to a setting in the middle.
    Thanks for all of your help!
     
  20. Brian Bunge

    Brian Bunge Producer

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    Scott,

    Sounds to me like you are good to go! All your tests seemed to have worked fine. That's exactly the type of tests you should do with each cable.

    Brian
     

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