Mesa Bass Head

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Jiffy_Jeff, Feb 26, 2009.

  1. Jiffy_Jeff

    Jiffy_Jeff Playin Tunes and Having Fun! Silver Supporting Member

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    I finally traded a bass for a mesa boogie 400+.

    The guy I got it from told me that it did have a problem; the fuses kept blowing. So I figured what the heck, I'll trade, put a some cash into it and have a great amp. I traded for an MIM jazz bass. I had almost no $$ into the bass, and I was not using it..


    Here is where I would like some tech advice.
    Got it home and plugged it in. The jewel light comes on, but the fan does not come on, and the power tubes are not coming on(heating up). Fuse looks good.

    I am going to have the tubes checked.

    Maybe a Power Transformer???

    Do any of you fine folks have any ideas on what the problem could be? Maybe something small, and work on up to the big stuff?

    Even if I had to have a new Power Transformer put in, I'm still in this thing for well under $500.00. A new transformer is $250.00

    Any help would be greatly appreciated. I know its tough to internet diagnose things, but this is a great place to ask!

    Thanks
    __________________
     
  2. mike80

    mike80 Member

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    If your jewel light comes on, the power tranny should be good. Check for a high voltage fuse somewhere inside.

    I would also check for burnt screen resistors too.

    Best bet is to take it to a tech.
     
  3. FrankieSixxxgun

    FrankieSixxxgun Member

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    The jewel light in most amps is based on the wall voltage getting in, that's all. The PT could still be popped as the heaters come on after the power gets to the PT. I'd personally take that one to a tech, doesn't sound like something simple or cheap to diagnose, I mean, unless you have trannys laying around.

    You're also required to come back with a tone report! I wanna know what a 400 watt Mesa bass head sounds like. My bassist plays a 300 watt Ampeg and it's murder, that's gotta be armageddon!
     
  4. Jiffy_Jeff

    Jiffy_Jeff Playin Tunes and Having Fun! Silver Supporting Member

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    Well its gonna be a while before this thing gets to the tech. Unless I ship it. Ouch 45 pounds!

    That's why I came here. To try to get an idea of what maybe to expext.
    There are 12 power tubes and 4 preamp tubes in this monster. At least one of them should have come on. Unles all 12 are blown.

    But as far as me lookin inside. Ill take a quick look but I aint goin millin roundin that snake pit.

    Thanks
     
  5. FrankieSixxxgun

    FrankieSixxxgun Member

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    None of them light up what-so-ever? Could be two things that pop into my head:

    A.) The heater lines from the PT are disconnected. I dunno about Mesa amps, but in other amps the heater lines run to the last power tube and then daisy chain down the line to light all the tubes up. If the initial power tube's heater lines are disconnected, none will light. Normally that'd tap the chassis and blow a fuse, but you might be lucky and just have it sitting on some other wire.

    B.) Blown PT. Could simply not be supplying the heaters at all, and that'd be a bummer and a few hundred to replace probably.

    Be CAREFUL if you decide to go inside that amp! The cap cans inside that beast will definitely kill you if they discharge across your chest. You should be able to bleed them through pin 1 of V1 with an alligator clip to the chassis like most amps, but make sure you stick a DMM on those cap cans to make sure they're not holding serious voltage before you assume they're discharged. Also, make sure you take the alligator clip off of V1 before you fire it back up, well, unless you like fireworks. ;)
     
  6. doctord02

    doctord02 Member

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    Also, dont go powering it up with out a speaker or load box plugged in to the output jacks. That can kill your output transformer. Honestly, if you dont have experience troubleshooting high voltage tube amps, just take it to a tech. A finger the wrong place or a slipped screwdriver and you could get electrocuted.
     
  7. Jiffy_Jeff

    Jiffy_Jeff Playin Tunes and Having Fun! Silver Supporting Member

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    Im not a tech, but know enough not to feel around inside a tube amp...... And not to power it up without a load.

    I put forth some problems in hopes of getting ideas of what could be wrong.

    Yes, its hard to diagnose over the internet.

    I appreciate the concerns for my health and safety, and the help.
     

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