Need help troubleshooting RTA-12C crossover...

jon s
jon s Posts: 905
edited July 2008 in Troubleshooting
I got this posted in the vintage speakers thread but no answers so i am posting here... i have a Polk RTA12C where the tweeter has no output (the midbass drivers were fine). the polycap on the crossover was blown so I bypassed the polycap and there was still no sound from the tweeter. checked the continuity on the tweeter and it looked okay.just as a confirmation, i replaced the tweeter with another, still no sound... any ideas where to look now?
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  • danger boy
    danger boy Posts: 15,722
    edited June 2008
    does that model have fuses on the back of it? if so.. check them out and replace if needed.
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    edited June 2008
    Hello,
    There should be a Polyswitch, a small tan colored disc, that is the first component in the path to the tweeter. It is possible that is open and no audio would reach the tweeter. That speaker has a fairly complex high pass filter section for the tweeter. Do you happen to have a Volt/Ohm meter that could read AC Voltages?
    Regards, Ken
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  • jon s
    jon s Posts: 905
    edited June 2008
    Kenneth Swauger wrote: »
    Hello,
    There should be a Polyswitch, a small tan colored disc, that is the first component in the path to the tweeter. It is possible that is open and no audio would reach the tweeter. That speaker has a fairly complex high pass filter section for the tweeter. Do you happen to have a Volt/Ohm meter that could read AC Voltages?
    Regards, Ken

    I bypassed the blown polyswitch and it still did not work... I do have a multimeter but not familiar with its functions... I just used it to measure DC and AC voltages before.
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  • [Deleted User]
    [Deleted User] Posts: 7,658
    edited June 2008
    Hello,
    The idea is to trace the audio signal from where it comes into the crossover and makes its way to the tweeter. So, with a low level signal being fed to the speaker and the meter set to read AC Voltage place the negative probe on the negative terminal of the speaker. Now with the positive probe placed in the positive terminal of the speaker you should see the meter's display giving a steady stream of numbers going up and down in value. This is happening because the incoming audio signal is constantly changing the frequency and level. Now that you have an idea of what is supposed to look like, use the positive probe to follow the audio path. If you find the meter's numbers going up and down before a capacitor, but not coming out of the capacitor (I know this isn't how capacitors really work, but this will help follow the theme) then somethings wrong with the capacitor. But this isn't going to be a perfect testing method because the crossover network has lots of other paths that can "fool" the meter into giving a reading even though that particular part is faulty. But it might give you a beginning, the ideal testing would be to remove the "exit" end of each part you are testing from the circuit board and test that part seperated from the rest of the circuitry.
    I hope this helps.
    Regards, Ken
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  • jon s
    jon s Posts: 905
    edited July 2008
    isolated problem to a bad 2.2uf cap... but unfortunately it took the SL2000 driver with it...
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  • jon s
    jon s Posts: 905
    edited July 2008
    replaced all the caps with Sonicaps, bypassed the polyswitch , replaced the SL2000s with RDO194-1s and removed the 750pf bypass caps. Sounds wonderful.... you can read more here...
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  • avguytx
    avguytx Posts: 1,628
    edited July 2008
    Awesome!

    Now, enjoy the music!
    Richard? Who's your favorite Little Rascal? Alfalfa? Or is it........................Spanky?.................................Sinner.
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