#32 M-Audio (Avid) Fast Track C600 teardown & repair

This little bugger, an M-Audio / Avid Fast Track C600, was listed as faulty on eBay - description said it would no longer power up, regardless of it being bus-powered or having its own external power supply connected. Got it shipped for 30eu / $30, so why not?

Reasonably comprehensive I/O complement, if i may say so myself, both front and back. And the inclusion of output selection, as well as transport controls, was a nice touch. Bit of a shame the tact-switches are the quite-high-actuation-force versions, stiff and clacky, which gives them a pretty cheap feel - i would've preferred a more soft-touch version, but that's just me. And since i'm not planning to keep it, i won't even bother considering replacing them.

"Obviously", the first thing to do is to rip the sucker apart, right? Now, sadly, i didn't have the presence of spirit of snapping internal photos before quickly troubleshooting it and removing the problem-component, but surely you can use your imagination to make up for my... enthusiasm, let's call it.

Top lid comes off (after removing four screws on the bottom and undoing two VERY stiff clips along the front & back edges), and after disconnecting all the cabling, 'tis all laid bare. The name is Bond - James Bond. No, wait, what?

Not exactly what i'd call a cut-rate job. Amphenol connectors (XLR combos and stacked 1/4" jacks) on the back, all name-brand chips, but that's all slightly let down by the no-name 1/4" jacks on the front edge, kinda crappy looking/feeling. But at least they bothered with heatshrink over the wire-to-pin solder joints on those, so there's that.

The brains of the operation is the Dream SAM3308B. The datasheet mentions it contains a microcontroller, as well as an audio router, and more interestingly, 8 DSP blocks. As it turns out, as i hadn't researched the unit too much beforehand, it does apparently have on-board reverb and delay effects, which is nice. The bigger chip next to it is an NXP (or nowadays, ST-NXP Wireless) ISP1582B USB peripheral controller. The S/PDIF's handled by an AKM AK4114VQ transceiver.

The output section is comprised of the AKM AK4358VQ 8-channel DAC, of which the first two channels go to the first pair of headphones, and the other six are the line-outs. Output low-pass filters / output buffers are three TI TLC2274C quad opamps, and two JRC NJM3414A's handle the headphone outputs themselves.

On the input side, two AKM AK5386VT handle the analog-to-digital conversion, two TI TLC2272C's buffer (and likely, or possibly, attenuate) the signals going into the ADC's, and a Fairchild/ OnSemi NDS9407 P-channel MOSFET, which my suspicion is, is soft-switching the main phantom power rail, which then is split up between the two pairs of mic inputs. Also, an AKM AK4382AT is the DAC for the second headphone output, with another TLC2272C as the output filter/buffer.

Not much to write home about, on the bottom side of the main board - the odd passive components, plus a handful of transistors likely doing some muting of the outputs on power-up/down.

Back side of the top lid is positively barren, save for the cabling connections.

The top side is a bit more "eventful", shall we say. Some shift-registers (74HC595)driving the input level meters, and others (74HC165) reading the button states. On the analog side, the mic preamps are four THAT1510's, with some TL072's after them, and one more that handles the two instrument inputs.

I liked the "nipple-lens" LED's on this board, you don't see those very often. Bit of a shame that, despite that, the slits in the top lid through which these shine, are as narrow as they are.

One more nice touch - the potentiometer knobs have a compliant rubber insert. That means that, as opposed to the more usual one-piece all-plastic ones, they won't loosen up in time, and risk sliding off. As a side-effect, due to the good grip and sealing, they were a right bastard to remove, what with the vacuum forming inside when pulling them off.


Right, time to get down to business, then. As mentioned earlier, i unfortunately only have "after" photos of the problem-area. After popping the lid off, since the thing wouldn't seem to power on at all, the obvious prime-suspect was the power supply section. Nice of the M-Audio / Avid engineers to have conveniently and clearly label some of the test-points for the various voltages. The L1 inductor was removed in order to have some "maneuvering space" - it's really cramped in there!

"P18" in the north-west of the circled area checked out just fine for the 1.8V rail. "P33" on the other hand (south-west), not so much - reading 1.5V or so. That's not gonna power on anything now, will it? After removing power, a resistance-check showed the 3.3V rail being within 13 ohms of ground.

I've revived several laptops in the past (and just the other day, the display in a 32" Vestel TV) by simply replacing a / the internally-shorted ceramic cap that was at fault. That wasn't the case here (hence the flux residue on the one nearest to the 3.3V test-point). Out comes the hot-air wand, and whaddya know - once the chip came off, no more short-circuit. Surprise, surprise...

Fortunately, it was a brand-name part as well, a Linear Technologies (nowadays, Analog Devices) LTC3407 dual synchronous buck regulator, so tracking down the cryptic "LTABA" marking was easy enough. Sanity-check, ie. measuring between the 3.3V "output" pin and the ground-connected belly-pad showed the same 13 ohms i had measured on the board.

Utterly tiny little bastard, ain't it? Micro-USB and Lightning connectors for scale ("banana for scale" wouldn't have worked, you'd likely barely even see the chip). Sure, i could've looked it up from the big distributors (Mouser etc), but since i didn't need to order anything else, shelling out 15-20$ for the shipping alone was a no-go. Fortunately there's (still) eBay, found an LTC3407A-2 from a seller who seems to be some sort of Element14 "reseller" of sorts, for about 10$ shipped. Slightly higher output capability (800mA vs. 600mA) than the original one, and higher-frequency too (2.25MHz vs. 1.5MHz) - Hopefully that won't upset things... TOO-too much.

Looking good from both sides, and upon plugging a USB cable in... Ta-daaa - 1.73V and 3.2V, well within tolerances (about 3-4% off, no biggie). I'm callin' this one fixed.