how do you fix blown inputs on a Mbox2?

  • Thread starter Thread starter Red Ribbon
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Red Ribbon

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hey guys. i have a Mbox2 and Mbox2 mini both with blown inputs. or that's what i'm guessing. when i enable the track to record there is a steady signal already half way up without me making a noise. there's also some crackling. even with no mic plugged in. if i record something the signal comes out distorted.

i think i've been using a bad mic-cable. or maybe i'm just don't know something about mbox safety.

any knowledge on this fixable or not would help, Thanks.

Colin
The Red Ribbon Army
theredribbonarmy.com
 
Depends how confident you are but the first thing would be to turn off phantom power and use a known to work cable.

If that's no good, go to a visual inspection.

Take the covers off and see if there's anything obviously burned out or blown.

If you do have blown inputs on both units, then there's probably something that you've 'done' to both of them.

Check your cables for continuity between pins.
I guess if phantom power was bleeding through to ground it would cause problems.
 
I'll have to look around the drive. I just might have it.
 
have i missed some really obvious joke?
I do that sometimes.
 
I don"t think it"s Blown inputs , the Term "Blown Inputs" doesn"t really mean anything as you can"t really "Blow" inputs unless you plug a high voltage AC source into the inputs (or DC but the Phantom power blocking capacitors would block that or the capacitors would blow) which would be quite rare occurance .....

If you used a dodgy cable it could short the phantom power to ground which would put strain of the 48V regulator but the 6.8k Phantom resistors would limit the current as to prevent a total short and in theory prevent damage to the regulator ......

I would say the problem probably lies in either the DC Blocking Caps have gone bad (they are in the direct signal path with the mic input) , or the power supply for the preamp has a problem , if the power supply were to put out a much lower voltage or uneven voltage between +/- it would cause the input opamp to clip at a much lower input signal ......

If you had an audio probe and a tone generator you could try tracing the signal from the input to see where the signal goes bad and you could test the supply voltages for the opamps and phantom power to see if they are in the normal range (probably between +/-12vDC and +/-18vDC and 48vDC for the phantom power) ......

Of cource the problem could be in other places like on the digital side , if you Mbox has analoge outputs you can test to see if the analogue outputs sound normal to try to determine if the problem is on the Analogue part of the curcuit or the digital part .....

Otherwize take it to a tech .....

Cheers
 
Great article …Thanks for your great information, the contents are quiet interesting. I will be waiting for your next post.
 
To sum up Minion's post...

If you are not an experienced, geared-up electronics tech, you have no chance of repairing those pieces of gear, yourself.


Your options:

1. Use it, as-is. Work around the problem.
2. Buy another one. Keep the old one(s) around for parts, until you realize, ten years from now, that you won't ever use anything from them, and throw them out.
3. Toss them out now, and buy something else that may be more reliable. Expect to pay about twice as much- which is the same you would have paid if you had bought the better stuff first time around. Call it a life lesson.
4. Bring it to a shop for repair, pay a bench fee ($65 is the going rate here in Atlanta) and get a repair estimate of about 1.5 to 3 times what it will cost to replace (See #3, above.) Call it a life lesson.

Oh, please recycle. There are electronics recycling places in most any town.
 
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