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Tonitz
06-26-2012, 04:41 PM
I've got a Presonus Firebox (http://www.presonus.com/products/detail.aspx?productid=4). 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).

http://i48.photobucket.com/albums/f206/tonitz/20120626_162733.jpg

thehadgi
06-26-2012, 04:44 PM
Going to avoid making the obvious firebox pun here lol

Too late :ninja:

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

Divercity
06-26-2012, 05:15 PM
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
06-26-2012, 06:15 PM
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
06-26-2012, 07:49 PM
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
06-26-2012, 08:00 PM
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
06-26-2012, 09:00 PM
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... (http://www.talkbass.com/forum/f34/electronics-geeks-needed-circuit-board-repair-694977/)

Tonitz
06-27-2012, 01:58 PM
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... (http://www.talkbass.com/forum/f34/electronics-geeks-needed-circuit-board-repair-694977/)

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
06-27-2012, 02:25 PM
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 (http://www.radioshack.com/product/index.jsp?productId=2062731). 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
06-27-2012, 02:34 PM
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.

Tonitz
06-27-2012, 03:17 PM
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.

Yeah another friend told me basically the same thing. He said "The goo is the laquer from the windings in the transformer. It got hot enough to make it liquid again." He's about your age and has been a recording engineer all his life and he also repairs most of his own gear. So I believe this to be true.




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.


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

I've given it a pretty thorough cleaning. I noticed there was a big difference between the brown goo oozing directly from the transformer and the brown fiber-like stuff from the blown capacitor (see pic below). The fragments of the blown capacitor cleaned up rather easily, and it looks to me like that resistor you mentioned may not be blown after all, and it was just collateral damage left behind from the capacitor in the original pic that made it to appear shot. The brown goo from the transformer wouldn't budge.

http://i48.photobucket.com/albums/f206/tonitz/20120627_145741.jpg

Anyway, I plan on replacing the capacitor. I've just got a few issues. When I first took the unit apart I noticed the blown capacitor right away. I lifted off the cap not thinking to check the polarity (there is a negative symbol on one side of the cap). Now I'm not sure which way to install it. Presonus doesn't make available the electrical flow of the unit so is there any other way to figure this out?

Also the issue I keep coming back to is the transformer. If I'm powering it with DC, and the transformer's sole purpose is to convert AC to DC, then why is it getting so hot to the point of melting itself? Shouldn't electrical signal be bypassing the part completely? Given it's close proximity to the blown capacitor, I worry that by simply replacing the capacitor I could run into the same problem in the near future.

drzinc
06-27-2012, 03:41 PM
Firewire supplies 500mA of 12VDC power, by the way.

http://support.apple.com/kb/HT2952


Power
Input voltage range: 8 to 33 V
Input power: approximately 0.3 W
Output voltage range: 12 V to 30 V (varies by product)
Output power: minimum of 7 W per port

djpenguin
06-27-2012, 03:46 PM
I would think that any parts that were damaged or destroyed would need to be replaced before the sound card will work properly again.

Transformers don't convert AC to DC. They use inductance to convert voltage by stepping it up/down. The number of copper wire windings on each side determines the conversion factor. That little three-legged jim-jam directly above the transformer looks like a voltage regulator, so it's possible that the internals of the sound card use a voltage other than 12V, and the transformer/regulator combo supplies that.

*EDIT* I just looked up the spec sheet for the AMD CMOS flash memory boot chip, and it has an input voltage range of 2.7-3.6VDC. The transformer is definitely necessary for normal operation.

I have the same soundcard sitting in a box downstairs. I can open it up and determine which direction that capacitor should be installed. That's probably the best thing to do short of having the schematics to refer to.

djpenguin
06-27-2012, 04:02 PM
The capacitor should be aligned the same as it's neighbor above and to the right of it in your pic, with the negative side oriented towards the top of the picture



http://support.apple.com/kb/HT2952

That's the design spec from the mid-eighties. As implemented in computers and old iPod power supplies, IEEE1394a ports deliver a maximum of 500mA@12VDC. That's what the IEEE1394a ports on this audio interface will be expecting to see.

drzinc
06-27-2012, 04:16 PM
The capacitor should be aligned the same as it's neighbor above and to the right of it in your pic, with the negative side oriented towards the top of the picture




That's the design spec from the mid-eighties. As implemented in computers and old iPod power supplies, IEEE1394a ports deliver a maximum of 500mA@12VDC. That's what the IEEE1394a ports on this audio interface will be expecting to see.


I understand that, but if a component fails in a device the full voltage/amperage may flood into the device causing more damage.

djpenguin
06-27-2012, 04:30 PM
I understand that, but if a component fails in a device the full voltage/amperage may flood into the device causing more damage.

You are correct, but unless something went wrong with the voltage supply (computer) end of this particular setup, the 1394 controller in the computer should not be allowing more than 500mA@12VDC to be drawn. I'd have to do some research to be sure, but I think the max voltage and current values for 1394 are typically seen only in repeater/extender type devices.

Tonitz
06-27-2012, 06:00 PM
The capacitor should be aligned the same as it's neighbor above and to the right of it in your pic, with the negative side oriented towards the top of the picture.

Awesome. What are the odds that you just had one laying around. Thanks for taking the time to look!

djlotus
06-27-2012, 06:13 PM
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.

This. Transformers are usually coated and most have an electrolyte between the copper wire and the "iron core", which is actually a magnet and shaped like a square. It would appear your unit took a surge and blew up. The surge would cause over current through through the primary leads on the transformer which would in turn send over current out of the secondary. If the board is not properly protected, which it appears it is not, the over current will blow all kinds of components starting with smallest resistance. You def have a blown cap there and most likely that resistor is shot also. If you are to fix yourself you are looking at replacing the transformer, cap, resistor, most likely a diode or two, and possibly the little guy to the top left of the blown cap.