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QSC RMX 5050 Failure

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djkeet View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djkeet Quote  Post ReplyReply Direct Link To This Post Posted: 16 January 2013 at 11:23pm
This is sounding like a design flaw in the power supply stage under powered/inferior caps and like anything in life this puts pressure on other things give it a couple more years we might hear more cases like this
NB.my simplistic analysis
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357- Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2013 at 2:22am
May also have been a case of cheap, bodged repair by previous owner.

This is why I say, if buying used amp to keep, get it checked and serviced the day you buy it.

Numerous 4050HDs have passed thru my hands, and none have ever developed that problem.




Edited by levyte357- - 17 January 2013 at 2:23am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote taurusty Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2013 at 5:40am
Ahhm, this is one of six amps bought brand new. 
I added the seventh (also brand new) on the 29th of December last.
 
Yes Elliott, I suppose the warranty is voided.
Have lost faith in the brand neways...!


Edited by taurusty - 17 January 2013 at 5:41am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357- Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2013 at 10:06am
Originally posted by taurusty taurusty wrote:

Have lost faith in the brand neways...!


To be honest, I know 5050s & 4050s are used as 4 ohm stereo sub amps in JA a lot, never understood this.

IMHO, neither suitable for this, unless using 400Wrms drivers.

IIRC, aren't the transformers rated at something silly like 800VA each or something?




Edited by levyte357- - 17 January 2013 at 10:12am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote taurusty Quote  Post ReplyReply Direct Link To This Post Posted: 17 January 2013 at 1:36pm
Agreed.
Most use it 2 ohm stereo. they recognise that it sounds way different from an MXa but i guess it's the cheapest brand amp available here.
 
There's a thread on here where I even saw  one culprit using it on dual T18 hybrids 1 ohm one side for 3 years w/o a problem!
 
Dunno the xformer rating, cking the scematics...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2013 at 10:57pm
I am always changing caps in QSC amps. It doesn't matter whether it is a chinese RMX with chinese capacitors or an american MX with american capacitors, they eventually bulge and sometimes leak & flash over. Electrolytics have a limited lifespan and some amps run them harder than others.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote levyte357- Quote  Post ReplyReply Direct Link To This Post Posted: 22 January 2013 at 11:11pm
Originally posted by kedwardsleisure kedwardsleisure wrote:

I am always changing caps in QSC amps. It doesn't matter whether it is a chinese RMX with chinese capacitors or an american MX with american capacitors, they eventually bulge and sometimes leak & flash over. Electrolytics have a limited lifespan and some amps run them harder than others.


Would lower rated transformers, place extra strain on the smoothing ?

Sure the transformers in 4050HD, are not same spec as those in Macrotech MA2400.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Muckerbarnes1 Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 1:35am
Lev, the rating of the TX and caps in PSU are very relevant. Some VERY old amps with bolt on high ripple caps are still working fine.
 
If the TX is lower VA rated and the TX o/p voltage falls the ripple current across the cap may increase. Caps work harder and fail.
 
If the TX is the same voltage and insufficient VA the same may apply as the TX saturates and voltage falls. Caps fail again.
 
Big TX. Big caps. Job done.  It's all relevant with 50Hz psu. Different with SMPS, but still not cured or perfect.
 
I have amps here near 30 years old with perfect caps that have been thrashed for years, so there you have it. Caps are very important, as is TX.
 
Yes smaller VA rated TX would put extra strain on smoothing caps, less strain on high capacity Hi ripple caps. i.e. expensive ones, which are more capable.
 
Much the same scenario really.  You pay for what you get.. Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dub Specialist Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 1:54am
thats explains it then mucker that why thay use these beasts then.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Muckerbarnes1 Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 2:17am
Oooo.. Class sub busters... no probs with caps there, even when a zillion years old prototype.
 
Enjoy that Jayson. One come back last month from 1992 for the first time....
 
Billy dawg likes this baby 1500 VA one.
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 9:28am
In the interest of fairness to QSC I should point out that there are certain failure modes on class H and G amps that reverse bias the capacitors, there are also failure modes which double the supply voltage to them, in both cases it simply involves failure of the cascode diode and/or one or more switching fets, reverse bias any capacitor and it will pass into history, so it may have been the end result of a chain reaction that damaged the cap, add to that the fact that simply shorting a cap to the ironwork or even missing it out of circuit shouldn't cause that kind of damage.
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