Need to test and check for a possible blown cab, where to start?

Discussion in 'Amps and Cabs [BG]' started by NikonGunny, Dec 14, 2016.


  1. NikonGunny

    NikonGunny Guest

    Dec 4, 2016
    i have an opportunity to purchase a Mesa PH212 at a cheap price.

    However...

    The only catch is that there is no sound coming from the drivers, but the horn still works. I don't have much experience with these cabs, but where would be a good place to start? The seller has given me permission to do some inspecting so long as I don't tear it completely apart without plopping down some cash and buying it. Super cool guy and I find that to be completely fair.

    What I know -

    He was playing through it using a Fender Silverface Bassman. I don't know which particular model in that family, but I can't imagine he was pumping enough wattage through it to blow the drivers. Maybe I'm wrong, who knows, since strange things can happen with electronics. I just know that those cabs are tanks and it should take quite a bit before they let loose. According to him the sound was there one minute and it was gone the next. No warning, no speakers frying, no smell, just gone. Like I mentioned above, the horn still works.

    Should I give this cab a chance and buy it cheap and repair, or should I run?
     
  2. Stumbo

    Stumbo Guest

    Feb 11, 2008
    Worst case scenario, you'll have to replace the speakers. I suggest pricing replacements and factoring them into your offer.
     
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  3. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    Best case scenario would probably be, there's just a bad connection somewhere in the cab.

    Gently and evenly push on each woofer to see if it moves freely without any scratchy sounds.

    Assuming they both pass that test, remove both woofers and function-test them individually. You can do this by touching a 9 volt battery to the + and - terminals. The woofer cone should jump when you do so. While you have the woofers out, eyeball the crossover and anything else you can see for signs that something got overheated.

    If both woofers are good and the crossover looks good, then the odds go up that the problem is just a bad connection somewhere in the cab, which you can probably track down and fix on your own.

    If the owner won't let you take the woofers out, but you still want the cab, I suggest making an offer based on the assumption that both woofers will have to be replaced. Like Stumbo said.
     
    Last edited: Dec 14, 2016
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  4. BadExample

    BadExample

    Jan 21, 2016
    Injiana
    Do this by spreading your fingers out wide around the dust cap and press evenly. Less a problem with MI speakers than others, but they need to go in and out straight.
     
  5. NikonGunny

    NikonGunny Guest

    Dec 4, 2016
    Replacement drivers from Mesa are $150-160 each. I'm familiar with the battery test since I've done it on another cab before. He's offering it for $300, which if I had to replace both drivers would put it back up to $600. That's where I've seen them sold for on the used market in working condition in my area. I'm not afraid to dig into its guts if need be, I just want to do so respectfully before I shell out the cash.

    What can I see by opening up the back panel? My plan was to at least take the grill off and do that.
     
    agedhorse likes this.
  6. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    If you fix the issue, the price is going to go way up.

    Break the problem down into sub sections and look at one at a time.

    -Check the input connectors, clean the contacts with deoxit if there is oxidation.

    -Check the connections running from the input connectors to the crossover, from the crossover to the speakers.

    -Inspect the crossover for any signs of a burnt component. In particular, check the signal pathway related to the woffers.

    At the very least you will need an ohm meter to test continuity.
     
    Last edited: Dec 14, 2016
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  7. NikonGunny

    NikonGunny Guest

    Dec 4, 2016
    Here's a good question - If I end up buying it and the drivers are blown, would I be able to replace the 16ohm drivers with 8ohm drivers (making it a 4ohm cab) without having to modify anything else?
     
  8. BadExample

    BadExample

    Jan 21, 2016
    Injiana
    That depends on the crossover, your willingness to discard it (bypass it) and if the range of the new drivers would be acceptable without the tweet or mid that it crosses to.
     
  9. beans-on-toast

    beans-on-toast

    Aug 7, 2008
    Although you don't know if the cabinet has been abused, the chance of two blown drivers is less than that of a bad connection.

    If you disconnect the woffers and test each one by measuring the resistance across the terminals, you will know if the coil is blown. An 8 ohm speaker will read less than 8 ohms. If it reads a high resistance (infinity) the coil is open. You can also do the battery test that Duke mentioned on each speaker, don't do it at the input jack
     
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  10. NikonGunny

    NikonGunny Guest

    Dec 4, 2016
    That's great advice about the measuring the resistance and the process to do so. I plan to bring a multimeter and every tool I'd need to do a field strip (that's a nod to all you shooters out there :) ). If he'll let me go as far as removing a driver I will absolutely do so.

    I'm really just hoping for a bad connection or a faulty crossover.
     
    beans-on-toast likes this.
  11. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    Have you tried to play the cab with your amp and a different speaker cable or is the cab info just what you've been told?
    Next question for me would be if the amp and cable used at the time of the failure have been used successfully with other cabs since the event.

    Those are robust cabs in every area from their structure to the audio and electronic components. It seems odd that the cab would be playing fine one minute, and with no obvious signs of distress what so ever, both speakers suddenly stopped working like someone "pulled the plug".

    Some elementary troubleshooting as has been suggested will likely get you to the problem pretty quickly, and I'll be surprised if both speakers simply failed simultaneously. It really sounds like an electrical connection somewhere along the signal chain and quite possibly in the area of the input jack/crossover/internal wiring. Best of luck!
     
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  12. NikonGunny

    NikonGunny Guest

    Dec 4, 2016
    This is all what I've been told. The plan is to go check out the cab in person tomorrow and do some testing with my own amp and cables. I fully agree about their robustness and is why I asked a whole bunch of questions as to what he was doing when it went out. He said they were playing loud (subjective) and the drivers just stopped working, but the horn is still active. I may get there, plug in, and the thing ends up working fine. In all my years of playing I've never been able to kill a driver, but I did blow a tweeter in an SWR cab which was super simple to replace.
     
  13. Al Kraft

    Al Kraft Supporting Member

    May 2, 2016
    Northern Virginia
    Of all the cab components I've ever seen fail in over 40 years in bands, it's almost always the HF driver (or protection device) that gives out first when a cab is pushed too hard. For the horn to survive while two high end bass speakers died just isn't consistent with my experience. Hopefully you'll find a working bargain!
     
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  14. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    Excellent point.
     
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  15. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    I am going to make another suggestion... I really recommend verifying that the drivers are in fact the factory drivers and that nobody did a switch-a-roo. I have seen a couple situations recently where what was in the cabinet was a cheap Chinese replacement driver in place of the (expensive) factory drivers.

    When buying pro audio (I used to buy, use and sell a lot of pro level gear) I would always check to be sure the drivers were correct. Some of the pro audio drivers cost $300-$600 each so there was a lot of incentive to substitute with $150 drivers and resell the factory ones.
     
  16. NikonGunny

    NikonGunny Guest

    Dec 4, 2016
    Definitely an excellent point and it's my experience as well since it happened to me with the tweeter dying.

    Very good suggestion! I'm going to do my best to try and pull one of the drivers before I hand over some cash. I think that is going to be my best route to determining what the heck is going on.
     
    Al Kraft likes this.
  17. guy n. cognito

    guy n. cognito Secret Agent Member

    Dec 28, 2005
    Nashville, TN
    I'm surprised we got to post 11 before this point was made. This is absolutely the place to start.
     
  18. NikonGunny

    NikonGunny Guest

    Dec 4, 2016
    The point didn't really need to be made at all since that's the first thing on my to-do list. My personal amp, cables, and tools are coming with me to do the testing. After talking to the seller about what happened I have been just as perplexed as you all regarding the circumstance that put it into its current comatose state. I didn't know if there had been a weird problem with that cab and connections or crossovers failing. I know it's Mesa and the quality is top notch, but things happen. If he truly managed to blow those drivers, I'll be impressed. They're not cheaply made nor are they cheap in price.
     
    Al Kraft likes this.
  19. Stumbo

    Stumbo Guest

    Feb 11, 2008
    If you discover the problem is that it's a faulty connection or something similar and fix it, is the guy still going to sell you the cab for the cheap price? I'd work this out before going through all the work you're planning to do.
     
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  20. NikonGunny

    NikonGunny Guest

    Dec 4, 2016
    Excellent question. I went over that with him and I even suggested that he should take it up to Mesa in Hollywood (I'm in SoCal) and have them take a look at it. I know the the value of the cab, he certainly does as well, and I wouldn't want someone to part with a really killer rig like that if there is a simple fix. He was super cool and expressed wanting it to live in a new home with someone who was going to invest their own effort into fixing it. I believe he's also a guitar player and having a non-functioning bass cab around isn't something he needs right now. Tis the season as well and he may just need some cash.

    I think at this point I'm going to try and be a minimalist in my evaluation. I'll at least hook it up to my amp and press on the drivers. If I can for sure tell they have been blown I'll likely walk away since that's a $300+ repair if I use Mesa parts. I certainly don't need a $300 paperweight sitting around either.
     
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