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Hart
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Joined: 03 Jan 2006
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 Posted: Thu Apr 12, 2007 4:12 pm Post subject: Busted caps? |
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Some of you guys are probably more familiar with this stuff than I.
I've got a cheapo preamp I'm going to sell. I was looking at one problem and found this:
See the brown sticky looking stuff? Digging back in my memory makes me think it's a dead capacitor... or maybe not since I can't find one that's bulging or anything. Other than the lights being out in the vu meters (the original problem) the unit seems to be working fine.
Thoughts?
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glittlefield
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| Posted: Thu Apr 12, 2007 6:03 pm Post subject: |
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Hard to say since I can't make out the icky brown stuff too well. There's a website that deals mostly with capacitors in PCs, but it might be worth checking out their forum:
http://www.badcaps.net
I've dealt with so many Dell Optiplex GX270's and 280's that I looked for popped tops on your caps at first. But the specific capacitor used in those models (as well as some Apple G5's and some HP models) numbers in the millions, so who knows what else they were used in?
Best way to tell... Put the amp in the middle of a concrete floor with nothing else around it and leave it on for a few weeks and see how long it actually stays on... ...and what kind of smell it emits.
(Oooh... look! 500!)
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Hart
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| Posted: Thu Apr 12, 2007 7:03 pm Post subject: |
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Some guys over at recording.org had the answer I believe. Apparently that is an epoxy used to help secure the capacitors. Now that they mention it, I can see where the brown "goo" looks like it's been applied as oppposed to looking like it leaked everywhere.
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glittlefield
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| Posted: Thu Apr 12, 2007 7:16 pm Post subject: |
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| Hart wrote: | | Some guys over at recording.org had the answer I believe. Apparently that is an epoxy used to help secure the capacitors. Now that they mention it, I can see where the brown "goo" looks like it's been applied as oppposed to looking like it leaked everywhere. |
Makes sense. I think that caps that 'splode look more like old flashlight batteries when they leak.
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TheVoiceOfBob
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| Posted: Thu Apr 12, 2007 7:20 pm Post subject: |
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Ahhhh! A place for my 16 years of working in the manufacturing area for IBM!
You are correct though, most likely it is just some adhesive for temporarily securing the caps or some flux, depending on what process they were using to solder the components.
Caps that burst from overheated dielectric or bad manufacturing of the caps, (kudos for pointing out the GX270s and 280s that have the bulging caps problem. Dell has actually extended the warranty for those models) will pop their tops. That's why there are those "X"s on the tops. Weakened areas to "control" where the outgassing will occur. Rechargable batteries do the same thing, they have vent holes so they don't build up pressure and explode, causing more damage.
Did you fix the original issue BTW?
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Hart
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| Posted: Thu Apr 12, 2007 7:27 pm Post subject: |
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No not yet. There are two vu meters on the front, one for each channel and neither are lighting up. I assumed it was a fuse but I can't find one. I suppose it's possible both lights blew but I haven't checked yet. There are a few more screws that have to come out for that.
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TheVoiceOfBob
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| Posted: Thu Apr 12, 2007 7:35 pm Post subject: |
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| Hart wrote: | | No not yet. There are two vu meters on the front, one for each channel and neither are lighting up. I assumed it was a fuse but I can't find one. I suppose it's possible both lights blew but I haven't checked yet. There are a few more screws that have to come out for that. |
If you know the connectors for the lights, you can use an ohm meter to check to see if you have continuity. Even though you can't always get an accurate reading while devices are still in the circuit (other paths for current flow) since you are checking the bulbs, it should be a very low, pretty much a short. If it's any higher than that, they are blown.
I agree, pretty doubtful. Especially if it's two seperate bulbs.
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Hart
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| Posted: Thu Apr 12, 2007 7:45 pm Post subject: |
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Ahh, to heck with it. That's too hard to get to.
If you look in my second picture.. see the black square at the bottom? Just below that is the meter. Not only do you have to remove those two screws, but that little black square is soldered to the main circuit board by way of 5 long metal bars that have something to do with some led lights apparently. Then I'd have to do it again for the other channel.
Gee... undo all that, look at the meters, try to put it all back together and pray it works... or just list it on craigslist as is and knock a few bucks off because the lights don't work.
Thanks for all the help.
p.s. you know it's cheap gear when the manufacturer adds little orange lights around the "tube" to make sure you can see it glow. I can't believe I let the salesman talk me into this gem.
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glittlefield
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| Posted: Fri Apr 13, 2007 5:47 am Post subject: |
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| TheVoiceOfBob wrote: | | Caps that burst from overheated dielectric or bad manufacturing of the caps, (kudos for pointing out the GX270s and 280s that have the bulging caps problem. Dell has actually extended the warranty for those models) will pop their tops. That's why there are those "X"s on the tops. |
It got to a point where, if I called even the most basic consumer support line and said "I have a GX270 with popped capacitors", they'd immediately start the process to replace the mobo.
I believe that warranty has been extended to five years, hasn't it?
And Brian, unless you LOVE working with soldering irons and the like, it's probably not worth messing with. 
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Hart
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| Posted: Fri Apr 13, 2007 6:10 am Post subject: |
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I agree. I don't mind pulling out the soldering iron and actually enjoy some projects but I doubt this one is worth the effort.
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TheVoiceOfBob
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| Posted: Fri Apr 13, 2007 6:16 am Post subject: |
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| glittlefield wrote: |
I believe that warranty has been extended to five years, hasn't it?
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Yup, and that goes for ANYTHING on those PCs, at least for us. So even if it isn't a MB replacement, they will honor the extended warranty.
With 5000 PCs on campus and a 3 year replacement cycle, we have quite a few of them!
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Hart
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Donovan
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| Posted: Fri Apr 13, 2007 3:10 pm Post subject: |
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More money for lunch! 
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Hart
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Edo
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| Posted: Sat Apr 14, 2007 7:12 pm Post subject: |
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Well my two eurocents then... the brown sticky stuff is the residue from overheated 'diëlectricum', the isolation between the capacitor plates. This can happen when you never switch off your unit. The fluid-like substance simply LEAKS out of the capacitor's casing. It can be dangerous stuff by the way, pretty toxic too.
It's obvious that the damaged capacitors are the power supply ones, normally functioning as limiting the DC ripple. If the elektrolyt capacitors lose their function, you will get an instable power supply, potentially resulting in severe damage to your circuit's electronic components. If it gets worse, it might even cause all controls and buttons of the unit go dead on you.
You'll need to replace the damaged capacitors... the sticky stuff acts like an acid, it can mean other components might be damaged. If you want to get rid of the sticky stuff easily, put the printed circuit board in your freezer for 2 hours, then use a toothpick to chip away the hardened residue. Afterwards, let the unit come back to room temperature before powering it up again. Don't force it.
Good luck! |
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