QSC Power amp issue, desperate for advice!

calmb4tehpwn · #1 02-09-2011, 06:10 PM

Alright, so I've picked up a QSC 2450. I check it out, and it seemed in decent working condition, some crackling when you change the output, but at max output it sounded fine. So I sold it, sent it out, and it was promptly returned to me. Now I have it back, and it's... acting weird. In bridge mono, if you crank one of the channel's output, and turn the other all the way down, it gives almost twice the volume of them both being turned up. Also, if you have the preamp volume up, and turn channel 1 down anywhere from 9 oclock to 3 oclock, it clips and resets. I've noticed just from looking at the vent in the front that there's a ton of dust in the amp. Would an overabundance of dust cause these issues? And if not, what could cause what I'm describing?

I'm happy to do some troubleshooting, just let me know what you need me to do, and I'll try it out. Anything that will help discover the root cause.

I really hope you guys can help, I need to sell it to finish my rig.

Passinwind · #2 02-09-2011, 07:06 PM

PM Bob Lee, a TB'er and QSC engineer.

calmb4tehpwn · #3 02-09-2011, 07:12 PM

Really? Thanks for the advice.

Passinwind · #4 02-09-2011, 07:16 PM

Quote:

Originally Posted by calmb4tehpwn

Really? Thanks for the advice.

Yep, he's been on here for many years and is a great guy to boot.

Bob would probably find your thread eventually, but if you had put QSC in the title it probably would've happened quicker.

billfitzmaurice · #5 02-09-2011, 08:21 PM

Quote:

Originally Posted by calmb4tehpwn

In bridge mono, if you crank one of the channel's output, and turn the other all the way down, it gives almost twice the volume of them both being turned up. .

I believe it's supposed to do that. Most amps when bridged only use one volume control. Consult your manual. I also don't think there's any benefit in running that amp bridged mono when one channel alone has all the power one really needs.

craig.p · #6 02-10-2011, 05:54 AM

If it were mine, I'd open it up, vacuum it out (gently!), and then reseat every internal connector a few times to scrape away any dirt/corrosion. And clean the pots while I'm in there.

Lots of possible causes, though. Bad component, flaky internal connector, cracked board (amp was dropped), loose ground... on and on.

PSPookie · #7 02-10-2011, 06:09 AM

It's thirsty. Give it a glass of water.

Growly Lytes · #8 02-10-2011, 06:12 AM

Best thing would be to try & clean out the guts of it.
I think i asked Bob & Agedhorse about this & they said to use a compressor to blow the crap out which i did.Anything else i used a vacuum with long nozzels to get into tight spots.
With the bridge thing i think when you set it to bridge you will get a heap of power from only channel one & channel two should be turned down so thats sounds normal but the gain jumps you described sound like dust has got the best of them but maybe thats not the problem at all so try cleaning first.
Spraying some electronic cleaner in & around the inside, inputs & outputs after cleaning it.

Bob Lee (QSC) · #9 02-10-2011, 10:08 AM

Is this an RMX2450?

By "change the output" do you mean you unplug the speaker cable from one output and plug it into the other? I would expect some crackling noise when you do that, but you should really always have the amp turned off when you connect or disconnect outputs. It's just good practice.

Also, please download the user manual: http://www.qscaudio.com/support/tech...er_manuals.php

calmb4tehpwn · #10 02-10-2011, 05:14 PM

Sorry, It is an RMX 2450, but by change the output, I meant to turn the decibels up or down.

I've got a long weekend, and plan on spending some quality time inside of it tomorrow cleaning it out. I really wish I had a static safe vacuum, but I'll make due. I'm in the IT field, so I have some experience cleaning electronic guts. Promise to take pictures of the hideous insides!

If cleaning does me nothing, I'll PM bob lee.

Also, I plan to sit down the manual, it's certainly a different beast than my drivecore.

calmb4tehpwn · #11 02-10-2011, 05:49 PM

Okay. Opened it up, poked around inside, there was a decent amount of dust, but nothing that would interfere with operation. I checked the connections, everything looks fine. Nothing looks clearly blown, or burnt. I've since done an a/b with my drivecore, and it's certainly roughly the same amount of power, which it should be.

It was returned to me, saying it was in non-working condition, though if the output isn't maxed, it crackles and clips, at max output, it comes through perfect. Maybe I just need to post it on ebay in "as is" condition. If I hadn't already bought a short rack case, I'd just sell the drivecore.

So have my specifics brought any issues to light?

I'd like this to -not- get returned to me again. Unless someone here wants it for a reasonable price?

calmb4tehpwn · #12 02-10-2011, 05:57 PM

Also, how much does a repair on something of this sort run? Not asking for quotes, just a ballpark.