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PA Amplifier blows fuses

Radio Shack 250 watt PA Amplifier keeps blowing fuses. This has worked for a year with no problem and one day, while in regular use, blew a fuse. The fuse has been replaced but continued to blow when the power is turned on. The correct fuse is being used (slow blow 7 Amp 250 W). Nothing has been added or removed or changed in any way, just all of a sudden stopped working.

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  • Shawna Jordan
    Shawna Jordan Mar 23, 2014

    This makes a lot of sense, however, there are no speakers connected. Once the fuse originally blew we unhooked all speakers and now there is nothing at all hooked to the PA Amplifier. We replaced the fuse and even the smaller internal fuses and only plugged it in the wall alone with nothing attached to it and once the power is turned on the fuse blows...

  •  Grubhead
    Grubhead Mar 26, 2014

    Speaker wires touching will permantely short out the power amp device, even when the wires are touching. The only cure is to replace the faulty device(s) that have shorted. If you are not certain which device has gone look at what is attached to the big heat sink. Each part will have a number on it. You can report them back here. However if you see something like the image below I would replace that as it will have gone.

  •  Grubhead
    Grubhead Mar 26, 2014

    Sorry that should read "when the wires are NOT touching".

  • Shawna Jordan
    Shawna Jordan Mar 26, 2014

    I don't see anything like your picture. Everything attached to the aluminum heat box has the same number...5W0..what looks like the omega symbol...22J

  •  Grubhead
    Grubhead Mar 31, 2014

    The devices are I think "N-channel power MOSFET" . One or more could have gone. You could try an Ohm meter across the terminals of each device. It's quite possible the short will show up on the faulty device. It will be just like you have touched the test probes together. The 1K setting on the Ohm meter is best for the test. Without seeing a picture of the device I can't say what part number it uses. My best guess would be the 22J being the part number. Possible 2SJ 22 (?) But you will have to do some research on it. If you find one that is faulty you could remove it and take it to an electrical parts shop who might be able to help track down a replacement.

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  • Radio Shack Master
  • 5,020 Answers

The fuse is blowing due to an overload. It's often and very likely caused by a transistor or ic that has gone short. The main culprits are the power transistors of the amp or whatever is on the big heat sink. Transistors will show the fault when you connect an ohmmeter to the terminals. It will be just like you have touched the test prods together! I don't think in your case it will be in the power supply. It's often caused by speaker cables that touch together.

Posted on Mar 23, 2014

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Posted on Jan 02, 2017

Thumbsmagee
  • 1 Answer

SOURCE: peavey classic 50/50 keeps blowing fuses.

Rob,

I have a classic 50/50 as well and re-tubed it with JJ el84s, vintage teslas and mullard 12at7s. As long as you replaced it with EL84s, I can't imagine that the output would be increased enough to damage the OT. When I got my 6505 Combo, one of the 6L6s was bad, and it kept blowing fuses and howling like a banshee. I would think that an OT problem would result in a significant loss of output...or none at all. I've gotten DOA tubes from a few places. I would suggest swapping each tube out 1 by 1, until you find it...if that is indeed the problem...before you pay the cash to have it worked on.

Posted on Oct 29, 2007

SOURCE: amp blows fuses

The fuses are there to protect the internals of the AMP.....
Please check that the correct fuses are installed......
if the incorrect ones are installed then a fire may develope...

There should be a manufacturers lable on the external chassis that details the fuses to use....

Fuses now days can be slow blow or fast blow....so the correct fuses must be used.....dont increase the fuse rating past the chassis panel label...but make sure they are correct...if they are correct then the amp needs a service to determine where the peak loadings to the power supply are originating from...

Some one may have installed incorrect fuses in the past...

Cheers from YUBEUT


Posted on Nov 03, 2007

  • 16 Answers

SOURCE: my bass guitar amp is blowing fuses

Hi ! I have a soluution and it is about to be published on http://www.howtodothings.com/electronics/how-to-fix-your-guitar-amplifier

Please check in a few days time

Posted on Dec 04, 2008

  • 54 Answers

SOURCE: Carver M-1.5t amp. blows 15 amp fuse.

First off....you didn't say if you are a tech or not. I'll make this really simple.

If you are not a seasoned tech with experience solving carver problems....you will waste tons of time and money guessing what the problem might be.

Carvers are quite the unique beast. They deliver whopping amounts of power in a small chassis. This is done by using a trick switching power supply. There can be any number of possible problems.

To properly diagnose this you will need an oscilloscope, signal generator, variac, and of course a really good quality multimeter that can test diodes and transistors.

IF and only IF you are a seasoned tech with all the above equipment, that has no experience repairing carver, then go online to ebay, find member techman777, and for around $15 you can get a nicely reprinted service manual. Troubleshooting expertise and the manual will take you foreward from there because the manual has a very thorough troubleshooting guide in it.

If you think you can fudge your way through the guide without any serious electronics knowledge, you are in for a rude shock as you will find that you are an earth man trying to read martian.

If you are just a casual fix it guy ( nothing wrong with that !!! ), I strongly suggest that you do NOT make this your first try at fixing an amp.

The value of these, in mint condition, all rebuilt is around $350- $450 on ebay all day long. if you are willing to invest that much, you can look up carver audio repair on google and send it off to them, as they are reported to do a nice job. OR....you can look me up on ebay, send it to me and I will do a nice job too, and that comes from 20+ years of repairing.

I know that this isn't much help, but carvers are very special, and require special knowledge to repair.

Best of luck.....Rob

Posted on Dec 16, 2008

petraman7
  • 1175 Answers

SOURCE: When I turn it on the fuse blows up.

Hi..
It will need service.
I would call the music store closest to you that sells PA gear and ask who fixes theirs.

Posted on Jan 12, 2009

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