Film-Tech Forum ARCHIVE: QSC 1400 crackle

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Posted by Brian Jupp (Member # 2801) on 08-21-2011, 03:45 AM:

I have a periodical crackle noise coming from a QSC 1400 amplifier. Sometimes it's loud, other times it's quiet. I have switched it between auditoriums so I know the problem is in the amp. Does anyone have any suggestions what part inside might need servicing? Or should I just get a replacement amplifier?

Thanks.

Posted by Monte L Fullmer (Member # 2797) on 08-21-2011, 03:48 AM:

maybe check with a dealer for repair options for those 1400's are definitely repairable.

Posted by Tony Bandiera Jr (Member # 2365) on 08-22-2011, 01:11 PM:

Dried out power supply caps....easy fix. Contact QSC's service Dept, they make a repair kit at a reasonable price. Or send it to them, they'll make it like new. Either way you'll get another 20+ years out of it.

Posted by Ron Lacheur (Member # 1126) on 08-22-2011, 03:26 PM:

Not sure if there's a local shop in Victoria to work on those amps but if need be, Backline in Vancouver is an factory authorized service center, although shipping 40lbs might be a deal breaker.

Posted by Bruce Hansen (Member # 281) on 08-22-2011, 05:56 PM:

I don't know that amp very well, but try switching switches back and forth (if it has any), and turn controls back and forth a few times (if it has any). Check connecions (if you moved the amp, you have already done this).

Posted by Brian Jupp (Member # 2801) on 08-23-2011, 01:50 PM:

Thanks for the input everyone. It turns out we have a few in company storage, so one is due in tomorrow. Once I pull the old one out I'll look at getting the crackly one repaired.

Posted by Ken Lackner (Member # 1002) on 08-25-2011, 07:40 AM:

quote: Bruce Hansen
and turn controls back and forth a few times

I've had dirty gain potentiometers cause this problem. If you turn the gain knob back and forth and the noise goes away, it is a bad pot. QSC sells replacement pots, and I'm sure you could find them at any major electronics supplier. It's a cheap and easy fix.

Posted by Louis Bornwasser (Member # 3063) on 08-25-2011, 08:44 PM:

WD-40 will clean any pot. Louis

Posted by Jim Cassedy (Member # 4115) on 08-25-2011, 09:36 PM:

I want to "second the motion" and agree with all those who suggested checking the switches & pots on the input modules on the back. Just about every noise problem or complete sound drop out I've had with a QSC amp originates with those switches or pots. Also you may want to actually pull the module and disconnect and re-connect it a few times to wipe those contacts clean too. I haven't had too many capacitor failures, but I noticed on the ones I've had that they were usually preceeded by "unusual" lighting of the 'overload' led on the front.

If it takes longer to go out after turning the 'trouble' amp on or if it comes on at a lower audio level than the other amps that are working properly, you might have a cap going bad.

I don't know that this happens 100% of the time, but I've observed it a couple of times before a power supply cap failure.

Posted by Bruce Hansen (Member # 281) on 08-28-2011, 05:05 PM:

quote: Louis Bornwasser
WD-40 will clean any pot.

With all due respect, Louis, WD-40 is a lubricant. To my understanding, it would be a bad idea to put a lubricant on contacts or a pot. It could make the problem worse.

If the pot has been sitting (unturned) for some time, you may just need to turn it back and forth about 20 times quickly. That may clean it.

Posted by Frank Cox (Member # 6258) on 08-28-2011, 05:49 PM:

There used to be some stuff in a spray can called TV Tuner Cleaner. In fact, I'm pretty sure I have a can of that in my projection room. That was supposed to be the real thing for cleaning volume controls and the like. I don't know if it's still available or not; I think my can came from Radio Shack.

Posted by Louis Bornwasser (Member # 3063) on 08-28-2011, 07:37 PM:

Believe it or not wd40 is better at pot-cleaning than any cleaner. It is NOT a lubricant. That is why you have to follow it with oil when used on metal to metal contact.

(The label even says electrical contact cleaner.) Louis

Posted by Bruce Hansen (Member # 281) on 08-29-2011, 05:00 PM:

The company says:

WD-40 Lubricates, Cleans, Protects, Penetrates & Displaces Moisture

Posted by Sam D. Chavez (Member # 1841) on 08-29-2011, 06:22 PM:

Maybe it's just a bad lubricant.

Posted by Mark Gulbrandsen (Member # 72) on 08-29-2011, 06:35 PM:

WD-40 was originally developed to keep moisture out of huge multi pin connectors used on early missles... probably before water tight connectors even existed. It is a good pot cleaner but one has to be careful about using it. Some pots are made with a plastic conductive resistive element. WD-40 is petrolium based and can attack the plastic on these over time... Know what you are sprayting it into before you spray...

Mark