Audio interface died, emitting smoke.

[Tonitz]

I've got a Presonus Firebox. Yesterday when I woke up I went into my studio and noticed that the light was off on the unit (it's always connected thru firewire so the light is always on). I unplugged it and plugged it back in, and smoke started pouring out of the back of the unit. I unplugged it immediately and when I tried plugging it in today nothing happened.

I talked to a tech support rep @ Presonus. He said he was 99% sure it was a blown capacitor, but they want $75 + shipping to fix it. I'd like to give a shot at fixing it myself. I took apart the unit, and after googling pics of blown capacitors I found the one that is bad and removed the cap (see pic below). I plan on replacing that capacitor, but my worry is the white square thing just below the blown capacitor. there seems to be brown goo oozing out of it. I don't know what this piece is or what it does.

Anybody familiar with electronics that can lead me in the right direction? I don't want to pay Presonus the money for the repair as I'd rather just buy a new unit (I only paid $100 for this unit initially).

[thehadgi]

Going to avoid making the obvious firebox pun here lol

Too late

Sucks though, good luck trying to fix! (I know nothing about circuits)

[Divercity]

You have to be really careful when resoldering capacitors dude. You can risk damaging the board and the iron has to be quite hot.


I would avoid doing it solo. A local I.T company might be able to do it for you. In my previous job we used to resolder capacitors for almost anything.

[Tonitz]

I've pretty much written the unit off as dead at this point. I'm not paying the $75 to fix it, so I don't mind hacking it up with a little bit of DIY and making it a little project. If I damage the unit beyond repair I'm ok with that, but hopefully I can pull it off. I'm just wondering what the hell that large white square thing at the bottom of the picture is. That brown goo can't be good.....

[Will MaXimal]

You will be fine... Just take your time and remember that you dont need much solder to attach a new capacitor to the board. The thing below seems to be a power distributer and the stuff coming out is an epoxy that holds it all together in the casing. It probably got really hot and started to expand and ooze.

This should not be a problem once the capacitor is fixed. Just keep a steady hand and remember... with a project like this you want to be gentle and less is best.

[Tonitz]

Yeah I've figured out that it's an ac/DC inverter. Although I used to plug it into an outlet when using my laptop, right now I only use it with my desktop and the power is supplied by the firewire connection.
If I'm not mistaken that's DC so that inverter is irrelevant, no?

Sent from my SPH-D710 using Tapatalk 2

[drzinc]

Looking at your circuit board it looks like more that the capacitor is faulty (blown) it looks like that transformer is leaking and the resistor beside the transistor got very hot (look at the leads). It probably took out more components also.

More info...

This seams like a common problem with these have a look here...

[Tonitz]

Looking at your circuit board it looks like more that the capacitor is faulty (blown) it looks like that transformer is leaking and the resistor beside the transistor got very hot (look at the leads). It probably took out more components also.

More info...

This seams like a common problem with these have a look here...

Thanks for the link. Upon digging a bit further it seems that this is a common problem, with many others running into the same issue with the same exact capacitor. What I'm still unclear about and mentioned in my earlier post is whether the firewire port on my computer supplies the unit with AC or DC power. I am assuming it would have to be DC as once the power cord from the wall hits my computer it is converted to DC. I could be wrong, but if you have direct current powering the interface, wouldn't you essentially be bypassing the transformer as no AC/DC conversion is needed? And if so why the hell is the transformer even getting hot and oozing brown goo in the first place?

[djpenguin]

Looking at your circuit board it looks like more that the capacitor is faulty (blown) it looks like that transformer is leaking and the resistor beside the transistor got very hot (look at the leads). It probably took out more components also.

What exactly would a transformer be leaking? It's just a couple of pieces of copper wire wrapped around an iron core (all solid parts, no liquids involved.)

Bad advice is worse than no advice, especially when it comes to electronics.


Tonitz: That capacitor blew rather spectacularly. The brown goo you see everywhere is the electrolytic gel from inside the capacitor. You're going to want to clean that up with isopropyl alcohol (90% or 99%) and cotton swabs.

Desoldering the capacitor is fairly simple if you have the proper tools. I recommend a dedicated desoldering iron like this one. Heat the iron up, squeeze the bulb and hold it, then tin the tip. Place the tip of the iron over the contact you wish to free, hold it there for five or six seconds (count it, don't guess), then release the pressure on the bulb. Some connections will free up the first time, some need a second pass.

From looking at your pic, it seems as though the SMD resistor above and to the left of the blown-out capacitor may have also been damaged. I suggest cleaning it (isopropyl and cotton swabs again) and then testing it with a multimeter to see if it's still presenting a proper resistance load. If not, you'll need to replace that too. Desoldering SMD stuff is tricky, you'll want to use a very fine-tipped soldering iron, reasonably low wattage (less than 50W), and some desoldering braid to remove the old solder. Take your time and be patient. It's likely to take multiple passes to free the resistor. Don't pull on it or wiggle it excessively, you might tear the traces off the PCB.

Firewire supplies 500mA of 12VDC power, by the way.

[drzinc]

What exactly would a transformer be leaking? It's just a couple of pieces of copper wire wrapped around an iron core (all solid parts, no liquids involved.)

Wires in a transformer are often coated with varnish or other substances and if heated enough this substance will melt and leak. I have been working with electronics since high school and I am 50 so figure out the length of time.