# Bad caps on amp???



## Irishdrunk

Picked this amp up today
MTX Thunder81000D from around 2000 I think

Don't have a test bench and don't feel like taking out my seats and hooking this up at the moment

Are these caps bad? Or are some supposed to bulge at the top?


















The guy I got it from said it wasn't working for him, but he's kind of an idiot and there wasn't even a remote wire hooked up when I took it out of his car....so...ya


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## 9mmmac

I'm going to say "probably bad" as everything I've ever heard says they are supposed to be flat. The bulging indicates some sort of bad chemical reaction beteween the components of the capacitor. The other indication of a bad cap is brwon goo leaking from the top or bottom. See any of that? 

I'd bench test it for a couple of days- just at idle for a while, then under load for as long as your power supply can keep up. The object is to force a falure under controled conditions, or verify proper operation under stressful conditions.

Of course, Murphy's law states that everything will test fine, untill you actually install it. Then it will burst into flames with a hot chick onboard, a trunk full of groceries or two toddlers in car seats. At night. Along an empty road. And your cellphone is dead.


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## bloobb

9mmmac said:


> Of course, Murphy's law states that everything will test fine, untill you actually install it. Then it will burst into flames with a hot chick onboard, a trunk full of groceries or two toddlers in car seats. At night. Along an empty road. And your cellphone is dead.


never fails


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## [email protected]

Im gonna say no, the top piece you are referring to comes like that. Those are snap in caps and those rarely go bad unlike leaded axial caps. That is just a plastic cap on the top. When caps go bad because of age, they leak, and thats just the leaded axial ones, and even at that it can be hard to tell. A snap in cap pretty much has to explode to be bad. Dont worry about it.


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## chad

push down on the tops, that material can deform with heat and it's likely not the aluminum relief bulging. Seen it before. If you push down and meet something hard/pointed then you need to certainly replace.


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## Mike_Dee

I'm 95% certain those caps are bad. They're easy to replace if you have any soldering skills, and a low powered soldering iron (30W). Make sure you note their polarity and replace them like you remove them. One side is + and the other -.


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## [email protected]

I have had new amps that come with the plastic caps deformed already.


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## Irishdrunk

I can push down on them, and they give way a little bit, nothing hard or pointy though, they just squish in a bit. Every other component on the board looks fine. The normal caps are all fine and flat, just those big suckers are bulgy, and if you look at pic there is one or two that are very bulgy and a few that are flat, that's why I was worried about it.

Don't have the ability to bench test at the moment


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## [email protected]

Irishdrunk said:


> I can push down on them, and they give way a little bit, nothing hard or pointy though, they just squish in a bit. Every other component on the board looks fine. The normal caps are all fine and flat, just those big suckers are bulgy, and if you look at pic there is one or two that are very bulgy and a few that are flat, that's why I was worried about it.
> 
> Don't have the ability to bench test at the moment


If you didnt feel anything under there, you are fine and dont need to worry about it. I have several old school amps that were used for 10+ years and the snap in look worse than yours, but there is nothing wrong with them.


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## Mike_Dee

Irishdrunk said:


> Don't have the ability to bench test at the moment


Well, if it doesn't work you'll know where to look. 

A good read about bulging capacitors:

http://www.capacitorlab.com/visible-failures/


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## Irishdrunk

Mike_Dee said:


> Well, if it doesn't work you'll know where to look.
> 
> A good read about bulging capacitors:
> 
> Capacitor Lab - Visual Signs of Capacitor Failure - Bulging and Leaking


Ive replaced several capacitors on lcd monitor pcb's before.
These big fat ones looked different and I wasn't sure if they were bad if bulged like the ones I'm used too in the link above


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## envisionelec

Mike_Dee said:


> Well, if it doesn't work you'll know where to look.
> 
> A good read about bulging capacitors:
> 
> Capacitor Lab - Visual Signs of Capacitor Failure - Bulging and Leaking


The plastic may be bulged, but there are several that I can see that have gone far beyond "normal" bulging.

If a capacitor gets hot enough to do that - it's not functioning properly and must be replaced.


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## Mike_Dee

envisionelec said:


> The plastic may be bulged, but there are several that I can see that have gone far beyond "normal" bulging.
> 
> If a capacitor gets hot enough to do that - it's not functioning properly and must be replaced.


We are in agreement.


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## chad

Rane MA6 caps used to do that from ambient heat inside the casing alone. And it was much larger and fan cooled. I honestly cannot remember the brand of the cap, the casing looked extremely similar but in my experience it's just not uncommon for ambient heat to do that to certain makes of plastic topped caps.


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## envisionelec

chad said:


> Rane MA6 caps used to do that from ambient heat inside the casing alone. And it was much larger and fan cooled. I honestly cannot remember the brand of the cap, the casing looked extremely similar but in my experience it's just not uncommon for ambient heat to do that to certain makes of plastic topped caps.


I don't disagree with anecdotal evidence, but these _are_ a known failure item on MTX Amps. 

Some of them are much worse than other. I would expect all to have similarly domed tops if it were an ambient heat issue.


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## chad

envisionelec said:


> I don't disagree with anecdotal evidence, but these _are_ a known failure item on MTX Amps.
> 
> Some of them are much worse than other. I would expect all to have similarly domed tops if it were an ambient heat issue.


They all are in one stage of doming or another and the one in the foreground that is not capped has shrunk it's jacket enough to look all goofy.

We are sitting on a situation that if he does not have means of bench testing then I would not recommend that user level to gut the amp and re-cap it. Granted it's not rocket science to some but to others it may be too much of a hassle. At which point one has to decide if parts/labor are really worth it.

But then again, I realize that I'm preaching to the choir


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## envisionelec

chad said:


> They all are in one stage of doming or another and the one in the foreground that is not capped has shrunk it's jacket enough to look all goofy.
> 
> We are sitting on a situation that if he does not have means of bench testing then *I would not recommend that user level* to gut the amp and re-cap it. Granted it's not rocket science to some but to others it may be too much of a hassle. At which point one has to decide if parts/labor are really worth it.
> 
> But then again, I realize that I'm preaching to the choir


Oh hell no. I don't recommend anyone fixing their own amplifier. It leads to hurt feelings and broken relationships...


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## chad

envisionelec said:


> Oh hell no. I don't recommend anyone fixing their own amplifier. It leads to hurt feelings and broken relationships...


and dependencies to methamphetamine and crack cocaine.


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## Irishdrunk

You guys are awesome, thanks for all the replies.

A friend that installs at the local Alpine dealer agreed to let me drop it off and he'll keep it on the test bench for a couple of days, put a load on it and what not, to see if it's ok.

I'm fairly confident I could replace these capacitors myself if I could find them somewhere, and they did indeed need replaced. After 4 beers my soldering skills are impeccable, after 8....not so much


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## chad

popping the caps out and replacing them is the cake part.... getting the amp apart and back together is what just sucks... sometimes those transistors get persistent... then you de-laminate a sil pad and piss yourself off.... if that amp has sil pads that is.


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