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My "ole faithful" Mesa Big Block 750 died last night...

Discussion in 'Amps and Cabs [BG]' started by Addison, Aug 3, 2012.


  1. Addison

    Addison This time, I didn't forget the gravy. Supporting Member

    Sep 17, 2009
    Bismarck, ND
    Graphic Designer, Social Media Manager - Zon Guitars
    UGH!

    What a great amp... I have run this thing HARD for the last five or 6 years and it finally crapped out.

    It's literally one of the first ones off the line... I immediately had problems with it (some weird effects loop thing) and sent it back to the factory... they did a bunch of updates under warranty and sent it back to me, and it has been my number one workhorse since then.

    Right when we were getting ready to soundcheck yesterday, I fired it up and played through it for about a minute or two... and then it was as if someone slowly turned the volume down into nothing. I let it sit for about 10 minutes while I helped with some lights... it worked great and then did the same thing.

    After that, I bypassed my pedalboard and power conditioner... plugged into the wall instead of our distro... tried different cables and switched speaker jacks... same thing.

    Took it home last night and tried a different cab... then I swapped out all of the tubes for a different set... same thing.

    Anyone know what this might be?

    I'm dying inside right now... I absolutely LOVE that head and I have babied it. It has been my number one tone monster for so long and so many gigs, I feel like I want to cry. :crying:

    Mesa is closed today... :bawl: ... so any insight from the board experts would be great!
     
  2. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    try putting a patch cable from fx send to fx return...
     
  3. +1, and clean the effect send/return jacks with DeOxit.
     
  4. Addison

    Addison This time, I didn't forget the gravy. Supporting Member

    Sep 17, 2009
    Bismarck, ND
    Graphic Designer, Social Media Manager - Zon Guitars
    Cool... I've read about that happening with Marshall heads, but I didn't think it would be the problem.

    When I sent the amp back to Mesa the first time, they installed an effects loop bypass switch because of some weird effects loop issue it had... I always leave the bypass switch on because I've never had an issue like this since they added that bypass switch.

    Do you think I could still be having the issue even if the effects loop is bypassed?

    Thanks!
     
  5. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    ah: maybe not.
    easy to try though.
     
  6. Addison

    Addison This time, I didn't forget the gravy. Supporting Member

    Sep 17, 2009
    Bismarck, ND
    Graphic Designer, Social Media Manager - Zon Guitars
    Ok, I'll try cleaning all the jacks and tube sockets on my lunch break today and then try running a jumper between send and return, just in case.

    What's the best way to clean the jacks... do I spray the male end of the cable and insert and repeat, or do I spray directly into the jack on the amp... or both?

    Thanks again!
     
  7. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    That problem sounds heat-related. Are the fans working?
     
  8. Addison

    Addison This time, I didn't forget the gravy. Supporting Member

    Sep 17, 2009
    Bismarck, ND
    Graphic Designer, Social Media Manager - Zon Guitars
    Yes... both fans are operating normally.
     
  9. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    LOL, I was sorta hoping you'd say they weren't.

    Pop the cover and vacuum that thing out. It might be full of dust/crud. Also check for any loose/corroded plug-in cables inside. Wouldn't hurt to re-seat every one. Snug up any internal screws you can find because sometimes they're crucial to ground/common connections.
     
  10. Addison

    Addison This time, I didn't forget the gravy. Supporting Member

    Sep 17, 2009
    Bismarck, ND
    Graphic Designer, Social Media Manager - Zon Guitars
    Yeah, I've done all that... I usually blow it out and snug everything up every 6 months or so.

    Anyway, I have an interesting update on this...

    My amp now works, but... in the process I uncovered something... you guys can tell me if it's "normal" or not.

    I went in and hosed down all the jacks and the tube sockets with DeOxit... let it sit for a few minutes... gave a cable some spray and proceded to plug it in and out of all the jacks a bunch of times to loosen up any possible corrosion. I then let it set for 10 minutes and plugged everything back in and powered it up.

    This time, after about 3 minutes of silence, I had about 3 seconds of audio before the slow fade to nothingness.

    So, I powered down... plugged a cable across the effects loop jacks as recommended... powered up... and this time it was complete silence. At that point, I got a little frustrated... so, with the power on, I took the effects loop cable and started rapidly plugging and unplugging it. When doing that, I started noticing sparks coming from one of the internal components. :eek:

    Here is the component in question... does it look "burnt" to you guys?

    [​IMG]

    I was so freaked out by it, I took video... it's in mov format:

    http://www.chrisandtheresa.com/addison_mesa_spark.mov

    If it doesn't work to click on the link directly, try right clicking it and saving it to your computer first.

    Anyway... I powered it down and started checking out the component and there are two of them leaning towards each other with wires coming out of the top, wrapped around each other. I took a rubber handled screwdriver and kind of prodded at the two wires... and although they were wrapped together, the wrap seemed loose. At that point I kind of nudged everything together, and made it a little tighter. Then, I checked all the fuses in that area to be safe, powered it up and bam... now it works.

    :hyper:

    I honestly have no idea if this was the problem or if it is a problem at all... it could work because I let the DeOxit sit long enough to penetrate the corrosion. Maybe one of the fuses I checked wasn't seated quite right... I have no idea. :eyebrow:

    Do any of you guys know if this behavior is normal, or could I maybe be onto something? Should I go ahead and drop a little blob of solder on those wires and make sure they're attached better?

    Any info on this would be great... I'm glad I got it working, but it'd be nice to know if it'll stay that way. :meh:
     
  11. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    what are the noises in that video?

    I'd say sparks are never good, IMO...
     
  12. Addison

    Addison This time, I didn't forget the gravy. Supporting Member

    Sep 17, 2009
    Bismarck, ND
    Graphic Designer, Social Media Manager - Zon Guitars
    It's me plugging and unplugging an instrument cable in and out of the effects send jack while the other side of it was plugged into the effects return.
     
  13. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    ah......
    I'd say get thee to an authorized service center, myself...before Something Bad Happens.
     
  14. Addison

    Addison This time, I didn't forget the gravy. Supporting Member

    Sep 17, 2009
    Bismarck, ND
    Graphic Designer, Social Media Manager - Zon Guitars
    Ugh... I was afraid you might say that...

    Unfortunately, I live in the middle of Nowhere, ND, so I'll probably have to send it in to MB on Monday.

    :bawl:
     
  15. Mulebagger

    Mulebagger

    Dec 12, 2007
    poppin in the corn belt
    Endorsing Artist: Zon Guitars, Tsunami Cables, DR Strings, GK
    Bummer that it died Addison.

    Mesa will fix it up. I sent back a walkabout head once for a different reason and they got it back to me in no time.
     
  16. dlb1001

    dlb1001

    Jan 30, 2007
    Looks like a couple of power, wirewound resistors, tied together in series. Something similar to this:
    http://www.parts-express.com/pe/showdetl.cfm?Partnumber=016-12
    May have pull off the PCB to see if the solder joint is still good. Also, it appears Mesa used some type of epoxy or silicone to anchor the resistors to the caps.
     
  17. From your description and the video (nicely done) it looks like a simple case of a cold soldier joint. If it works after you prodded them I think all you have to do is re-soldier that joint between the two resisters. If you can't soldier it yourself, you can ask any repair guy to help. They'll have it done in about 2 mins if you bring in the amp with the cover off. I'd suggest learning how to soldier yourself if you don't already know anyway. YouTube is your friend. A cheap soldiering iron and soldier shouldn't run you too much at the local hardware store. And you'll be able to repair your own speaker and patch cords down the road. That joint looks like its in a good place for even a novice to soldier. The resisters are high temp so the likelihood of damage is minimal, the joint is clearly on top and easily accessible with a soldier iron. I say go for it. It rather empowering to repair your own beloved amp. Pm me if your interested in tackling the job yourself and I can provide detailed soldiering instructions.
     
    punchdrunk likes this.
  18. Chef

    Chef Moderator Staff Member Supporting Member

    May 23, 2004
    Columbia MO
    Staff Reviewer; Bass Gear Magazine
    ^^^that right there is one of the things that makes TalkBass great.
     
  19. Addison

    Addison This time, I didn't forget the gravy. Supporting Member

    Sep 17, 2009
    Bismarck, ND
    Graphic Designer, Social Media Manager - Zon Guitars
    AWESOME...

    I'm quite an intermediate solder guy, actually... just last night I rewired my lefty Fender Hot Rod P-bass with all reverse audio taper pots and a fancy overpriced capacitor. :D

    I'll definitely give it a go... if the problem is as simple as that, I will be PUMPED!!!

    THANKS!!!

    :hyper:
     
  20. On the video, it looks like the arcing is coming from INSIDE the resistor.
     

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