trying to fix my m-audio interface

[birt]

one of my rare solid state projects.
my m-audio profire audio interface started losing channels. 2 out of 8 don't work anymore. the others sound a bit 'thin and mechanical' then i noticed there is some noise of loose parts inside. i suspected the jacks so i opened it up today.


two 22uF/25V on the board seemed to have lost their metal casing. it's just 2 wires with a bit of rolled up paper. and some specks on the inside of the chassis suggest the have flown off. has anyone ever seen this before?? (the brand is Suncap)


i hope replacing the caps will fix it :-)

[shooter]

seemed to have lost their metal casing

now you have the results, the fun part is what's the cause.  you can try replacing all the PS related E-caps, but I would expect something they feed is bad and will take 'em out.

got a schematic?

[HotBluePlates]

... two 22uF/25V on the board seemed to have lost their metal casing. ... some specks on the inside of the chassis suggest the have flown off. has anyone ever seen this before?? ...

It looks exactly like electrolytic caps which have had a reverse-polarity voltage applied.

The question is what applied the reverse voltage?  And why only 2 caps?

You'd like to have a schematic at this point.  You'll have to contact M-Audio for that, as their website only includes user manuals in the support section.
Any chance you hot-swapped mics (in/out of the jack with phantom power on) on those 2 channels?  Other M-Audio users have found damaged ICs and resistors after doing this, then finding out the hard way the 4 protection diodes (very likely the 3-leg Q-numbered parts right under the jacks) didn't offer enough protection.

Just wondering if some similar mechanism damaged your ICs, which then did strange things to the power supply for those channels...

[birt]

well it's on the output jacks. there could have been phantom power from a desk (i'm pretty sure in the 4 years i've been using this that must have happened several times) but i wouldn't think a device designed with balanced outputs would get damaged by phantom power from a mixing desk. that's the standard setup really..


i have never used the external power supply either. only bus powered from the computer..

[HotBluePlates]

I have no specific knowledge of M-Audio's stuff, and only searched based on your question.  Still, finding search results describing significant damage due to a common user error was a bit surprising.

I really couldn't venture a guess without looking at a schematic.

You can swap the caps & hope for the best... I hope there's nothing wrong with the SMD items on the board, as they often require a good temp-controlled iron with small tips (or specialized tips for DIP removal), liquid no-clean flux, and a good magnifier to see what you're doing.  SMD can be tricky, as parts can look like they're soldered in place properly and still not function (because the part's contacts aren't directly touching the pad on the board, but only bridged with solder).

[PRR]

> i wouldn't think a device designed with balanced outputs would get damaged by phantom power from a mixing desk. that's the standard setup really..

It's really not. Phantom is for mikes (and mike-equivalents like direct boxes), not a powered box.

Reverse voltage sure would blow-up caps, though reverse through Phantom resistors is less likely.

Replace the caps. You know values from the ones which have not exploded (yet?).

[birt]

> i wouldn't think a device designed with balanced outputs would get damaged by phantom power from a mixing desk. that's the standard setup really..

It's really not. Phantom is for mikes (and mike-equivalents like direct boxes), not a powered box.

Reverse voltage sure would blow-up caps, though reverse through Phantom resistors is less likely.

Replace the caps. You know values from the ones which have not exploded (yet?).

sure phantom is for mics. but loads of mixing desks have 1 phantom power switch for all channels. any XLR output device has a big chance of getting connected to a mixing desk right? i don't even know what else i would use that interface for..


anyway, i'll replace the caps and see what happens.