Help - killed both Cerwin Vega tweeters (or worse) with APM-200?

Discussion in 'Speakers' started by lokerola, Jan 12, 2018.

  1. gdmoore28

    gdmoore28 Super Member

    Messages:
    2,545
    Location:
    Central Arkansas
    Well, there is no point whatsoever in installing the glass fuses because they have been bypassed internally. The only way to utilize the glass fuses is to undo the bypass. Not hard to do, you will just need to remove the crossovers and reverse the changes that the PO made to them. If you intend to reintegrate the glass fuses, don't forget to order new fuse holder caps when you talk to Parts Express. They carry them. It would be very helpful to your helpers here if you posted very clear closeups of the crossover network.

    My guess is that the guys here are exactly right about the polyswitches being the problem. They are defective and are not allowing the tweets to tweet. And I'll further wager that you have been listening to them this way all along, but didn't realize it. Happens to the best of us.

    Just for your peace of mind, I'd take the cover off the APM200 power meters and take a peek inside. Make sure it hasn't been fiddled with and has no obvious problems.

    That's my useless 2 cents worth. ;)

    GeeDeeEmm
     

     

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  2. lokerola

    lokerola AK Subscriber Subscriber

    Messages:
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    Location:
    Alexandria, VA
    UPDATE - The tweeters must have never worked. Insert Homer Simpson "Doh!" here.

    I pulled one of crossovers and I see the problem. The wiring to the fuse looks good. But the tweeter cap (C4, 200wv, 2.5mfd on attached schematic) ISN'T on the circuit board. It's just chopped off.

    I'm going to crack open the other cabinet here in a few mins, but I expect I'll see the same.

    LOL. Good Lord.

    I think the plan will be to order the following from parts-express:
    - Two 200wv 2.5 caps
    - Two of the tweeter relays (just in case)
    - A pack of the glass fuses.

    Cross my fingers - I haven't soldered anything in 20 years.

    Schematic attached.

    Pics

    co2.jpeg

    co3.jpeg
     

    Attached Files:

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  3. lokerola

    lokerola AK Subscriber Subscriber

    Messages:
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    Never mind. The 2.k 200v cap is on the back of the circuit board. More Homer Doh required. I guess I'm down to the tweeter relay at this point?

    co4.jpeg
     
  4. Judas Priest

    Judas Priest Super Member

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    2,208
    Location:
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    Maybe you blew out your ears :)

    Sorry, coulnd´t resist :)
     
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  5. whoaru99

    whoaru99 Epic Member

    Messages:
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    The setting of the APM has ZERO to do with any speaker problem.

    All that 4/8 ohm setting does is scale to the meter reading. It does not in any way change what goes in or comes out of the unit.
     
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  6. goodolpg

    goodolpg Just an old fart trying to help. Subscriber

    OK, looked at the back of the APM-200 and there are 4 terminals, two for each channel....how did you have it wired?
    Did you run wires from the amp/receiver to the APM-200 and then out to the speakers?
    Or did you run wires to the APM and the speakers separately?
    I used to have a RS APM 500 meter and ran wires from the receiver to the meter and another set of wires from the receiver to the speakers, so each terminal on the receiver had two wires connected to red and black.
    Another way would be to run speakers off "A" on receiver and to meter off "B" and have speaker selected to "A + B".
    The ONLY way I can see the APM possibly damaging the CV's is if you ran wires to the APM and then off to the speakers from the APM and then assuming the APM is some how faulty. In that case the APM would be in series with the speakers, the other ways of connection I mentioned would have them running in parallel.
     
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  7. lokerola

    lokerola AK Subscriber Subscriber

    Messages:
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    Indeed! It appears I may have, LOL.


    Makes sense. The only odd thing is that I've cranked this amp and the CV's many times and never had an issue.

    I had 2 pairs of speaker wires coming out of the amp on the A channel. I added a short run of speaker wire to run to the APM, so each plug on A had 2 wires - one going to the speaker, one going to the APM. I did not run to the APM, then out to the speakers. But good question.
     
  8. lokerola

    lokerola AK Subscriber Subscriber

    Messages:
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    Location:
    Alexandria, VA
    Is there any way to bypass the little relays? Could I unsolder them and have the circuit work without anything in their place?

    Maybe I could remove the relays and solder in a short piece of wire on the pc board - just to see if bypassing the relays makes the tweeters come alive?

    Thoughts?

    Also - both circuit boards are the same.
     
  9. goodolpg

    goodolpg Just an old fart trying to help. Subscriber


    Ok, then I agree with the others who say the APM really should not have caused the tweeters to just up and quit working.
    And since you tried the tweeters wired direct to the receiver we know those work ok.
    My best guess, as others have mentioned, is the problem is in the speaker itself and the crossover specifically.
    And it's not a really complex crossover so between the help from members here and you doing the work I'd think you'll have them up and running soon and for not that much money.

    Again, speculation on my part, but the schematic that was linked to plus the crossover board you posted, looks like "t" or "T" means it is part of the tweeter circuit.
    Accordingly "m" or "M" is midrange and "w" or "W" is woofer.
     
  10. gdmoore28

    gdmoore28 Super Member

    Messages:
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    Location:
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    You can do that. You are simply bypassing the tweeter protection. If the tweets work when you bypass the relays, just be careful not to overdrive them while you wait for the new relays. I'd certainly try it.

    (And keep in mind that if some other problem blew the tweets, that problem will still be there when you bypass the protection, and may blow the tweets. My suspicion, though, is that this problem originated with the original owner, or just bad relays. I'd still try it. But that's just me.)

    GeeDeeemm
     
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  11. Grenadeslio

    Grenadeslio Super Member

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    1,674
    Hell ya, best way to check those little bastards lol, plus he has tunelidge while he waits. But PE is very fast with delivery, the wait won't be long.
     
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  12. lokerola

    lokerola AK Subscriber Subscriber

    Messages:
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    Thanks guys. I’ll see if I can bypass one of the relays tonight and report back the results.
     
  13. N8Nagel

    N8Nagel AK Subscriber Subscriber

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    you could just clip a test lead across the tweeter protector, I'm assuming it's the little yellow thing that looks like a disc cap on the x-over board. If it works then, then you know that either replacing it or removing it and replacing it with a jumper wire will make your speakers sing again.
     
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  14. I LIKE MUSIC

    I LIKE MUSIC Super Member

    To be clear, the device in question is not a relay. It is a PTC (positive temperature coefficient) device. That is its opposition (resistance) to the signal increases (it goes open) with an increase in temperature. Its temperature increases as the power to the speaker driver increases.

    It is also called a poly switch.

    It is basically a passive temperature controlled switch. When it is cool it is on and when it reaches a certain temperature (heated by the power passing through it, the more power the hotter) it turns off.

    I mention this because if the OP looks for a replacement and calls it a relay, it may make it difficult to locate.

    And of course my OCDness is in full force...
     
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  15. 63pontiacgp

    63pontiacgp "Tubes Smell Good" Subscriber

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    As mhardy6647 pointed out the Realistic meter (I still have the one I've had since new in '81) simply looks at voltage. It hooks up parallel with the amp. It does not affect the load the amp sees significantly. The 4 or 8 ohm setting is simply for scaling relative power output. If however you reversed polarity to the meter it could cause problems. It's common grounded internally so amp could potentially see a short to ground if the meter leads are backwards. Shouldn't affect speakers though.

    Mike
     
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  16. gdmoore28

    gdmoore28 Super Member

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    Excellent point, Mike!

    GeeDeeEmm
     

     

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  17. mhardy6647

    mhardy6647 AK Subscriber Subscriber

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    I don't see a whit of OCD in that reply :)
    I'm glad you mentioned it -- I was on the verge of doing so myself!
     
  18. gdmoore28

    gdmoore28 Super Member

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    Not even a smidgen? ;)

    GeeDeeEmm
     
  19. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Well it is definitely more than just a smidgen.
     
  20. Grenadeslio

    Grenadeslio Super Member

    Messages:
    1,674
    Moot point, many posts ago I already posted the replacement part from Parts Express for the OP, he knows what to order.
     

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