Bulging Capacitors on QSC MX1500

I just got a hold of a QSC MX1500 Power Amplifier from a local bar at a great price.
Upon opening the cover to clean it ,the capacitors look like they are bulging at the top.
Should i replace them ?
I was listening to it for at least 5 hours before i opened it and sounds really good .
It wasn't getting hot or smelling like smoke .
Thank You
 

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Hello,
SOMETIMES it can be just the plastic disc that is bulged because the high temperature surroundings.
If the aluminium can itself is bulged then you should replace them.
The caps are not bean can size so i think they can be replaced at modest cost by long life, nice specs available at a reputable company like Mouser.
Greetings, Eduard
 
Ex-Moderator
Joined 2002
Hi! It would be wise to select same physical dimensions so the new ones will fit and then either up the value ratings and/or voltage ratings a bit. If the old ones* were 10,000 µF 50V it won't hurt to have 12,000 µf 63V if these fit. It would also not hurt to use 10,000 µF 80V. Only where values are very small it would be OK to really up value if the rectifiers are up to it. Same diameter/width but a little shorter is no issue and might in some cases be beneficial for air flow/cooling.

My advice is to choose low ESR, long life 105 degree rated caps made by a reputable brand. As I experienced defective rectifiers in the past I tend to replace these together with the caps.

*BTW they are from 1987, I would not hesitate to replace them.
 
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@eduard Thank You ,after much research on the internet, you are correct ,the plastic disc bulge is mostly due to surrounded heat or lack of air from cooling fan(dirty fan).
And based on the cooling fan on this amplifier ,it was very dirty and clogged and air flow was not that great.
After taking out the cooling fan and thoroughly cleaning and using proper lubrication ,the air flow is much better!
 
Those are all so even and rounded, it really looks like just the plastic disc covering the end is warped. SLice off the plastic sleeve to remove the disc and find out. A fairly common occurrence.

The amp works and sounds good. I might hesitate before tearing out all those caps.
 
Ex-Moderator
Joined 2002
After having an old filter cap being launched (shorted internally when the amp was being measured) nearly missing my head I think having new ones when they are 34 years old AND have been overheated for a longer time as the fan did not function properly, is a better bet. Measuring them would be a wise idea too. In my experience age is a lesser problem than overheating as the latter causes the electrolyte to dry out.

Of course there is a chance they will work OK but when they go the woofers likely will also go if the device does not have DC protection.
 
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@H713 @jean-paul The Power amp is currently in the Audio Repair shop getting a look over and will be getting a tune up if it turns out it needs one due to it's age.
I will be updating the post when i receive notice on it's condition .
Thank You all for your input.
It is very much appreciated !
 
Be advised that most of the older QSC amps invert polarity at the output. The MX1500 is one of them. Also, some of those big caps are in the output stage signal path to the speakers, so their age will greatly affect sound quality, especially at the lowest and highest frequencies. I would recommend buying Nichicon, Panasonic or United Chemicon caps in the exact series and size format as the old ones. Do not be tempted to bypass the caps with smaller ones. It won't do much and just be a waste of money. Also replace the smaller caps on the driver stage rails. They are the first to fail and if you have the tell tail humming sound, its way overdue.

The fans on these amps usually last forever, even if they weren't cleaned. They would run very hot because of this, which is why your filter caps are all probably shot. Given the age and condition of the amp, I would re-cap the whole thing if you plan on keeping it.
 
Especially one that’s been used enough to build up that much dust. Those were some good amps - especially the non “a” version. Does your have the double banks of D424/B554 outputs?

Those rail caps are effectively in series with the output, but are within the feedback loop so degradation may not be noticeable unless you’re cranking it. And then it’s noticeable for sure - the usual symptom is significantly reduced power at clipping as the ESR skyrockets and capacitance diminishes.
 
Those are all so even and rounded, it really looks like just the plastic disc covering the end is warped. SLice off the plastic sleeve to remove the disc and find out. A fairly common occurrence.

The amp works and sounds good. I might hesitate before tearing out all those caps.


I tend to agree with Enzo. If it works, leave it alone. Bulging caps could be a problem but don't necessarily MEAN a problem.