48V blew up Mbox mic pres. Need service info.

[oldskool]

I'm pretty sure I destroyed the input section of my MBox 2 today. I was using improperly wired condensors and I'm pretty sure the mis-applied 48V blew the input chips or an analog supply rail.

Before I open up the Mbox, does anyone know:

What opamps are used in the mic/DI input section?
Are they surface mount? 8 or 14 pin SOIC's(/DIPS)?
How is USB power split into + and - rails?
Is this going to be an easy fix? Or should I send the darn thing in to Digi?

I've included the grim details below just in case anyone will recognise symptoms or has a similar problem:

Mbox was acting strange this morning. First both mic ins were ultra sensitive, overloading with the gain controls fully counterclockwise. Upon reboot both mic pre's have only very low level, and the gain controls have no effect on the level. The only effect that the gain controls have is to slightly attenuate the high frequencies of both input signals.

I was using the Mbox with phantom powered condensors, for the first time, and discovered that these new mics were wired incorrectly. I suspect that my frequent plugging/unplugging of these bad mics caused the Mbox to fail.

Now when I record audio, it is very low level, and only the + side of the waveform shows up. That's why I am suspecting that one of the supply rails is broken. The same symptoms apply to all of the inputs. This suggests to me that either they all share the same input amp, or the analog supply is broken. The interesting thing is that the analog output (monitor and headphone) works fine, which tells me that this section just uses the single supply rail, or the fault may not be with the analog supply. Convoluted, I know. Thanks for reading.

[Craig F]

I think the chips are surface mounted.
They are fairly easy to open up.
Just the 4 outer corner screws and the one that hold the base of the front panel on.
Then gently pull the sides outwards.

[oldskool]

Hey CraigF, you must be a little more adept at taking things apart than me! I broke a little piece of the plastic case while dissassembling the Mbox. Oh well, not a big deal to me.

The Mbox is jam packed with MAX4477's, which are Maxim's "wideband, low-noise, low-distortion op-amp", and operate on a single supply down to 2.7V! (Pretty cool chip, even though the slew rate is an atrocious 3V/usec, but with output swings of 5V max that is somewhat alleviated.) That blows my supply rail failure theory out of the water, and I'm going to have to poke around to see what I can see. I have a feeling I'm just going to end up sending it in, because I don't really have the time for this type on activity, but I'll post what I find, if anything.

Does anyone have schematics for the Mbox 2, or a link to online schematics?

[Craig F]

I put a thread-sert in 20 units a few years ago, for mounting in a lab.
It was cool no one could figure out how they were stuck to the desks.