Fried mid cap and tweeters Monitor 70s

Fosters
Fosters Posts: 5
edited August 2012 in Troubleshooting
I've been bi-amping my Monitor 70s and yesterday during a "home alone" listening session I managed to make it so that no more sound comes out of the top set of inputs. I'm somewhat of an electronics idiot, only thing I know is how to put a multimeter to things and see if they come up with a reading. The woofers all checked out, the tweeters did not produce any kind of ohm reading. I'm guessing they're fried unless it's some kind of feature of the tweeter design.

Then I tested the caps on the board, the high cap does produce a reading with the multimeter on 2000k- starts off in the negatives, then goes up to infinity. The mid cap just goes to 0 immediately, which according to the interwebs is a sign of a shorted cap.

The inductors and resistors tested good, is there anything else I should check?

I'm not an audiophile so not going to be rebuilding a whole new set of crossovers, but I figured since I need to replace the caps I'll get something nicer in there... any recommendations that won't break the bank and that would fit in there without too much hassle? Can I solder bigger caps on the back of the board? Looks like the high cap would be easier to replace since it's to the side of the board, but the mid cap looks like it will be a pain to get anything larger in there..

Thanks in advance!

ps. I have a party coming up this weekend... looks like I'm gonna have to dust off my trusty old JBL D315s from the garage :eek:
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Comments

  • F1nut
    F1nut Posts: 50,549
    edited August 2012
    You can't measure the resistance of electrolytic caps while the caps are on the board and even then it's better to test their uF value than resistance. That said, I seriously doubt any of the caps are bad, you simply fried the tweeters.

    I'll assmue you are "bi-amping" with an AVR. If so, that is not bi-amping. With most AVR's when you set it up to "bi-amp" you are actually reducing the available power to each channel and are more likely to induce clipping at a lower volume level.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

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  • Fosters
    Fosters Posts: 5
    edited August 2012
    Would frying the tweeters also stop the top 2 woofers from running? And that's good to know about the capacitor being on the board... how come the high cap did measure up correctly? Seems odd.

    So what's the next step, just replace the tweeters and see if the mids start working as well?
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  • F1nut
    F1nut Posts: 50,549
    edited August 2012
    how come the high cap did measure up correctly? Seems odd.

    It depends on what else is in the circuit, that's why you can't test them on the board.

    You're probably getting sound from the drivers, but without the tweeter playing it'll seem like there isn't much sound.

    You're much more likely to cook a resistor before any damage to a cap.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • Fosters
    Fosters Posts: 5
    edited August 2012
    I've tried the speakers individually with nothing but the top set of inputs hooked up to the receiver, and cranked up about half way, there really is nothing coming out. The top input also doesn't sniff anything when trying to read ohms, whereas the bottom inputs do. Can the whole top input be taken out by just the tweeters being fried?

    Thanks for the quick responses btw!
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  • F1nut
    F1nut Posts: 50,549
    edited August 2012
    The top posts should be for the tweeters only. You should get sound from the drivers with the bottom posts connected.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • cnh
    cnh Posts: 13,284
    edited August 2012
    I'm not sure how those speakers are wired, though I have a set. Supposedly a "cascade array" so that the top woofer overlaps with the three beneath it but slopes off the tweeter more gradually than the bottom three do. So I'd expect some sound from it. I'd go with what Jesse is telling you. If you go over to the discontinued models page for M-70s you will find several reviewers who fried tweeters on that model. It's actually fairly common and probably what you have there.

    If you're still in the warranty period just call up Polk Customer Service and get two tweeters, replace them and see if that solves the problem?

    And, BTW, Welcome to Club Polk!

    cnh
    Currently orbiting Bowie's Blackstar.!

    Polk Lsi-7s, Def Tech 8" sub, HK 3490, HK HD 990 (CDP/DAC), AKG Q701s
    [sig. changed on a monthly basis as I rotate in and out of my stash]
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  • Fosters
    Fosters Posts: 5
    edited August 2012
    F1nut wrote: »
    The top posts should be for the tweeters only. You should get sound from the drivers with the bottom posts connected.

    That would make a lot more sense actually. I'll definitely try the bottom inputs again and focus on all woofers, maybe pop them out and make sure they're not just moving like a passive radiator would.

    That gives me a whole new thing to search... upgraded tweeters.

    I'll contact Polk CS in the mean time.

    Thanks again!
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  • F1nut
    F1nut Posts: 50,549
    edited August 2012
    There are no upgraded tweeters for your speakers and besides, that's not the problem. You drove your AVR into clipping and clipping will cook any tweeter.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • Fosters
    Fosters Posts: 5
    edited August 2012
    I played a bit of Basstronics - Bass I love you, and yep, all 4 woofers want to jump out, so I guess it is just fried tweeters. Thanks everyone for the help :D Unfortunately I didn't get a chance to call early enough to catch the EST based polk CS, can't wait to get them fixed now... glad it's something simple :D
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