Any ideas what could've caused the bulging on the top of this capacitor? Apparently the amp has been recently serviced and given clean bill of health.
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Amp experts: Is there a fault with this cap?
- Thread starter Sparky Mark
- Start date
Agreed, looks like physical damage to me - something was dropped on it!
If a cap goes bad, it tends to bulge evenly across the top, like this:
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If a cap goes bad, it tends to bulge evenly across the top, like this:
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The capacitor failed due to several possibilities. It can happen. Don’t use the amp, have it repaired.
There is a wet paste inside the aluminum electrolytic capacitor. Excessive heat generated internally can cause it to expand. The top of this capacitor is designed to expand if this happens. Worst case it opens and the material leaks out.
See the aluminum electrolytic capacitor paragraph:
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There is a wet paste inside the aluminum electrolytic capacitor. Excessive heat generated internally can cause it to expand. The top of this capacitor is designed to expand if this happens. Worst case it opens and the material leaks out.
See the aluminum electrolytic capacitor paragraph:
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I, for one, would like to know who 'serviced' it, so I could thank them for missing something so obvious...
... I've seen and repaired computer motherboards (caps near the voltage regulator/power section), my A/C unit (starter cap), filter caps for load centers...
... all with same problem... intermittent, or not functioning as intended, with bulging caps as their visual clue...
... the humanity...
... I've seen and repaired computer motherboards (caps near the voltage regulator/power section), my A/C unit (starter cap), filter caps for load centers...
... all with same problem... intermittent, or not functioning as intended, with bulging caps as their visual clue...
... the humanity...
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Thank you for the responses. It's not my amp but it's currently for sale elsewhere. I'm not convinced it's impact damage, it looks more like something to do with heat. I doubt the adjacent tube could generate enough radiated heat to do this so internal failure (perhaps partial?) of this capacitor seems favourite to me.
You're right. The nearby tube would not have generated enough heat to cause the cap to do this. There is definitely a bulge that peaks between the two right hand digits (looking left to right). It may not be the classic type of bulge shown in post #3, but compared to its companion cap, you can see something isn't right.
It could still be some type of impact damage. But if it is, my quess would be that it happened before it was installed.
Assembly line workers not usually being electronics experts, I can see how this might have happened.
Regardless, even if it plays OK, something ain't right about this. I would not purchase the thing unless you are up for having it repaired, and hope there is nothing else wrong.
A marginal cap near a hot transformer can have a shorter life.
Most certainly... little harder to nail down, too, without a visual... good call... @Sparky Mark if you're truly interested in this, have a competent tech change both of those caps, bulging or not...
- Feb 12, 2006
- 60,978
- 5
- 220,743
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Physical deformities can lead to all kinds of incorrect assumptions.
The most likely cause is that the Lexan insulation disc on the top was a little off center when the case heatshrink material was shrunk down, pinching it at one part of the edge.
There's no way to know if the cap is bad without testing it, to definitively say it's bad from looking at it is not a responsible answer.
Same thing with the black cap and the bulged looking top, if the disc is slightly too large, it can bulge when the case insulation is shrunk down... leading to false conclusions as well.
Without testing, everything is just a wild ass guess. If I saw this, I would test for capacitance, ESR and leakage current at rated voltage. If it passes all these tests, I would leave it alone.
The most likely cause is that the Lexan insulation disc on the top was a little off center when the case heatshrink material was shrunk down, pinching it at one part of the edge.
There's no way to know if the cap is bad without testing it, to definitively say it's bad from looking at it is not a responsible answer.
Same thing with the black cap and the bulged looking top, if the disc is slightly too large, it can bulge when the case insulation is shrunk down... leading to false conclusions as well.
Without testing, everything is just a wild ass guess. If I saw this, I would test for capacitance, ESR and leakage current at rated voltage. If it passes all these tests, I would leave it alone.
This is a handwired amp, most likely from the Orange custom area so should have been subject to much greater scrutiny during manufacture than mass produced heads, therefore I am doubtful that the capacitor was like this when originally fitted.
I totally agree with the advice that the seller should have the issue fully checked out by a competent tech (ideally Orange Amps) and publish the result as part of the sale information.
I totally agree with the advice that the seller should have the issue fully checked out by a competent tech (ideally Orange Amps) and publish the result as part of the sale information.
Lacking the knowledge and test equipment to do this, do you think if a person were to have the cap replaced, that would be be a good plan B?
Nope. The capacitor might have failed on its own but in the process caused latent damage elsewhere. It might also have failed because something else went wrong first. Replacing a damaged part in isolation may not fix the cause or effect of its failure.
I never said that it would.
But in diagnosing failures, sometimes the only way to see what else is wrong is to fix the things you know (or suspect) are wrong, then see what else is working or not.
If this cap is in a power supply that runs the rest of the amp and it is shorted, you probably won't be able to determine what, if anything, else is failed or working until you fix the power supply.
- Feb 12, 2006
- 60,978
- 5
- 220,743
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
NO, because there is always risk of damage to PCBs and terminals when replacing a part.
It's no different than the guy who changes spark plugs every 3000 miles rather than when really needed (say every 50,000 miles) , and then at 50,000 miles ends up with a stripped thread in the head... now a very costly issue that otherwise wouldn't exist.
The top of this type of capacitor is designed to show any swelling due to internal pressure. Pressing on the top will tell you if the top black cover is simply misseated on the cap. If it presses down flat, without the indication of any bulging underneath, the cap could be fine.
Carefully cut the plastic wrapper enough to remove the black disk on top. Don't cut into the aluminum can. If the can isn't bulging underneath, it's just deformed plastic.
That would be my plan B.
Edit: Beans must have been typing the same time I was; his suggestion is good too.
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- Feb 12, 2006
- 60,978
- 5
- 220,743
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
I see this kind of thing regularly, 9 times out of 10, there's nothing at all wrong with the cap. If there is, it's generally more obvious with performance issues. When the Lexan disc is held at the edges and there is expansion of the material, it has to go somewhere, and the only place is up.
The Lexan disc is required on certain accessible caps where the case may be at a high enough voltage to cause a shock, and is required for some applications, especially where failure cold cause it to become energized. Some caps (depending on where they are used in a circuit), when shorted, can place lethal voltages on the case. Certain voltage doubler or voltage multiplier circuits fall into this category.
OK. I understand that.
But we are also not advising that capacitors be changed on a regular schedule as some sort of miguided preventative maintenance measure.
Then one just lets it go and does nothing.
As long as the amp works OK, that doesn't seem to be a problem.
But as someone buying this amp his options are to chance it with that cap, have the cap replaced or not buy it.
-edit- Looking at the OP's original pic, these caps don't apear to be mounted on a PC board.
If they are what I suspect they are, they are physically held in place on the chassis using the clamps at the base of the caps. Wiring would be directly to tabs coming out of the bottom of the caps, not to PC boards. This would IMO, make this a much easier replacement job with very little chance of any other damage caused by the replacement.
I could be wrong. It's early in the day and I've only been wrong twice so far.
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This is true, however I would expect in this instance any doubler capacitors to be better isolated from the chassis and have more substantial insulation on the clamp strap than just a shrink wrapped wrapper. In the old days the cans were completely exposed without any kind of wrapper at all.
I've opened up the wrapper on a few caps to check for suspected bulging like the original poster has shown; If all is well, I just apply a little bit of goop glue (very handy stuff around the bench) and glue the disk and wrapper edge back in place.
