QSC RMX1450 blowing Ch. A fuse

grievousangel · 6th January 2011, 03:10 PM

Hello All,

I have a QSC RMX1450 that has a dead Ch A and a OK Ch B. Ch A blows the B+ fuse on start up ASAP! I can lift the Ch A B+ rail leads from the main PCB and it does not blow the fuse.

I am waiting on a 22A Powerstat (variac) that I won on eBay to come in, but I am not real sure how to use apply the variac to get a soft start and not blow the B+ fuse.

Suggestions needed.

thanks,
billy

HighTec · 6th January 2011, 03:23 PM

Hm, what about fixing the dead channel first and then power up the whole unit?

llwhtt · 6th January 2011, 03:32 PM

If the Variac has a current meter you'll see the amp start to draw lots of current as soon as you start turning the Variac up. Normally as you start to turn the variac up you'll see a small current surge then it will subside as the filter capacitors charge up. Shorted output transistors most likely. If you look at the schematic you'll see the collectors are grounded and the emitters are connected to B+ rail. Once an output transistor shorts it's B+ to ground and blown fuses. The million dollar question is WHY?

Craig

6th January 2011, 03:10 PM	#1
grievousangel diyAudio Member Join Date: Mar 2004 Location: Statesboro, GA. 30461	QSC RMX1450 blowing Ch. A fuse Hello All, I have a QSC RMX1450 that has a dead Ch A and a OK Ch B. Ch A blows the B+ fuse on start up ASAP! I can lift the Ch A B+ rail leads from the main PCB and it does not blow the fuse. I am waiting on a 22A Powerstat (variac) that I won on eBay to come in, but I am not real sure how to use apply the variac to get a soft start and not blow the B+ fuse. Suggestions needed. thanks, billy

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6th January 2011, 03:23 PM	#2
HighTec diyAudio Member Join Date: Mar 2003 Location: Sibenik, Croatia	Hm, what about fixing the dead channel first and then power up the whole unit?

6th January 2011, 03:32 PM	#3
llwhtt diyAudio Member Join Date: Jun 2008	If the Variac has a current meter you'll see the amp start to draw lots of current as soon as you start turning the Variac up. Normally as you start to turn the variac up you'll see a small current surge then it will subside as the filter capacitors charge up. Shorted output transistors most likely. If you look at the schematic you'll see the collectors are grounded and the emitters are connected to B+ rail. Once an output transistor shorts it's B+ to ground and blown fuses. The million dollar question is WHY? Craig

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