Question about Marshall Amplification Marshall Amp Cover for AVT50H

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Marshall AVT 50 has loud buzzing noise when switched on and continues. Sounds resembles a fan... Amp is quite new. hardly used. Is it valve rattle? Louis.

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Posted on Jan 02, 2017

  • 1137 Answers

SOURCE: i have marshall 250 dfx when i turn it on cooling

Try carefully cleaning your cooling fan with qtips for the blades and a vacuumn. See if that helps the fan. If not it will need to be replaced. If you are experienced with amp repairs have a look for loose parts on the circuit board. If you can safely disassemble it, look at the soldered side for bad solder joints. From another poster on here with the same problem I have learned that resoldering R107 and R96 helped. Make sure they aren't burned out or have changed in value.They are in the FDD circuit. Have a look at your owners manual and it will make sense. The schematic is available here:http://www.ampix.org/displayimage.php?album=search&cat=0&pos=0 If it doesn't come up use the search function on that site. Do not attempt to service this yourself unless you are absolutely sure you won't hurt yourself or the amp.

Posted on Mar 05, 2010

  • 5603 Answers

SOURCE: I got marshall 410h bought it from USA I thought

Likely destroyed the rectifiers AND the filter capacitors. Replace the capacitors and the rectifiers. There are a lot of them. There are fuses so some of those may have saved some parts.

D10 through D14 and D16,D17 and D20,D21 Some of these may have survived so test each.

C51 and C52, C26,C34 probably gone. Check the Bias supply is working at expected bias voltage.

Your schematic: http://elektrotanya.com/marshall_jvm410.pdf/download.html

Posted on Feb 05, 2011

jcameo7270
  • 675 Answers

SOURCE: My Marshall Haze 40 Amp started making a very loud

may be one of the electrolytic capacitors in the power supply has become leaky...this is a common problem among amplifiers...so you let it cool down..then after a period of time the capacitor heats up and then causes the hum...the power supply caps filter out the 60 hertz ac line noise...which is probably the frequency of the sound it is making...this is a good indication of these caps going bad....another thing you can check is to see if the amp is properly grounded(eg: the ground pin on the plug is present) and that you dont have an open cord or input

Posted on Jul 10, 2011

  • 5603 Answers

SOURCE: When I switch my Marshall

Internal failure... take in for repair. It is NOT DIY unless you are electronically adept and have necessary equipment to repair it.

Posted on Sep 15, 2011

  • 1212 Answers

SOURCE: External Speaker hookup problem. I hooked up 2 external speakers (8 ohm, 160 watt) into my Marshall AVT 50 amp (tag on back says 4 ohm minimum). Everything worked fine, then I shut it down and now (ne

If you are competent with electronics, open it up and check the fuse(s). Especially if no lights come on. If you get voltage, then check the jacks you plugged into- they may have dirty interrupt contacts. When you plug the jack in- it opens those contacts that otherwise are closed making the circuit to the cabinet's built in speaker. Contact cleaner should clean them up if that is the issue.

While it is possible there is a power supply issue, you can see that quick with a voltmeter, it is not likely you did much more than blow a fuse.- very possible if you unplugged speakers with the amp operating..

If you think you killed it- you usually still get distorted noise.

Posted on Mar 30, 2012

Testimonial: "Thanks - I'll pass this on to the guy looking at it. I'd like to believe it's just a fuse, but I'm preparing for a blown output transformer. I'm still not sure why it blew - two 8 ohm speakers in parallel should be 4 ohms, and that's what the amp was rated for. Even when (for a short time) I had only 1 speaker hooked up, those 8 ohms would just decrease the efficiency, right, not cause the transformer to blow? Obviously, I'm trying to understand this so that it doesn't happen again! Thanks for your help!"

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External Speaker hookup problem. I hooked up 2 external speakers (8 ohm, 160 watt) into my Marshall AVT 50 amp (tag on back says 4 ohm minimum). Everything worked fine, then I shut it down and now (next...


If you are competent with electronics, open it up and check the fuse(s). Especially if no lights come on. If you get voltage, then check the jacks you plugged into- they may have dirty interrupt contacts. When you plug the jack in- it opens those contacts that otherwise are closed making the circuit to the cabinet's built in speaker. Contact cleaner should clean them up if that is the issue.

While it is possible there is a power supply issue, you can see that quick with a voltmeter, it is not likely you did much more than blow a fuse.- very possible if you unplugged speakers with the amp operating..

If you think you killed it- you usually still get distorted noise.

Mar 29, 2012 | Marshall Amplification Music

2 Answers

Low volume on my marshall


I am very new here and don't know how to answer a question to a specific problem so I will write about the most common problems that I have had over the decades doing guitar amp repairs. If you find that your amp is extremely low in volume and then suddenly comes back to normal- check out the effects return [or power amp in] jack. Especially in Marshall amps-these corrode and your signal dies. If there is loud noise such as hissing and crackling with no guitar patch cord in the input jack- the input jack is likely at fault. They normally have switching contacts that ground part of the input circuit when the 1/4 inch male plug is disconnected. When this in is corroded or too weak to make normal contact, you can get these symptoms. If your amp is a solid state Marshall or Fender and there is a random buzzing sound with no guitar signal connected- hit the side of the amp and listen for the buzz to go away or become louder-if it does, this usually means that the connections are loose at the two large filter capacitors. In one or more Marshall amps, they use a filter circuit in the low voltage power supple for the preamp tubes. If you encounter a dead Marshall[the model escapes me now] remove the circuit board and resolder the four connections at the bottom of the bridge rectifier. If you have any other amplifier repair questions you can email me direct at computerlen@hotmail.com.

Nov 14, 2011 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

Marshall MG100 MG DFX. Full speaker noise with all volume knobs turned to zero and on all settings. When the amp is switched on there is a horrible loud buzz/growl that can only be left on for a split...


well theres only 3 sections of the amp the problem can be in. Pre-amp, Power amp, or speaker. First Unhook the speaker. If you can turn on the amp after that and hear your guitar through the headphone jack this means your pre-amp is ok. at that point you can just take a voltmeter across the 2 terminals of the speaker to see if oyu have 4, 8, or 16 ohms. that'll prove the speakr is good. I'd also try to connect and disconnect the pedal a few times to see if the normals in the jack on the amp are just being stupid. if all this concludes no success, you sir have a power problem.

Aug 31, 2011 | Marshall Mg100dfx 100-Watt Combo Guitar...

3 Answers

I got a Marshall MG100HFX Amplifier for guitar. The problem is that whenever i turn treble switch on it gives clean sound as it should, but in couple seconds it fades away. When I turn the switch again it...


I haven't played or worked on a MG100HFX but I understand amp circuits very well. The behavior you are describing sounds to me like a bad capacitor in the Treble circuit. This is a problem that would require the skills of an experienced amp tech. If you are within your warranty period you might want to return it. If not, a good local repair shop should be able to diagnose the problem.

Good luck and keep rockin'!

Mar 01, 2011 | Marshall Amplification Marshall MG100HFX...

1 Answer

I have a buzzing noise through my MG50dfx every time I use the foot switch and have changed to the over dive/distorted sound. Any help would be wonderful?


Has it always done this? If it's just a mild hissing sound, chances are it's normal. If it's a loud obnoxious buzz, is your gain cranked all the way up? If it is, turn it down about half way and see if it goes away. If not, take it in to a good guitar store for service/diagnosis.

Feb 22, 2011 | Marshall Mg50dfx 50-Watt Combo Guitar...

1 Answer

When I turn the amp on it makes a loud squealing noise. If I turn it on and off again (several times) the amp will work normal. It doesn't do this all the time; but it is beginning to happen often. When it...


Have a look at this link:http://www.geofex.com/ampdbug/squeal.htm then Back to the Home Page. You may have a bad solder joint some place on the circuit board also. Unless you have experience with electronic repairs you are best served by consulting an accredited Marshall dealer and repair person as there are voltages present that can kill or injure you.

Aug 22, 2010 | Marshall Mg50dfx 50-Watt Combo Guitar...

3 Answers

Buzzing fan on a Marshall mg 100 head


Try to remove the fan and look for the sticker on the back side where the wires come out.

Remove the sticker, underneath it there will be a small aluminium cap (sometimes there is no cap and the axis is readily visible when you remove the sticker).

Take the cap off with a sharp tool (it shouldn't require a lot of force to do it), now you should be able to see the fan axis being held in place by a small clamp - put a drop or two of machine oil in there, move the fan blades a little to make the oil flow past the axis into the bearing.

Reinstall the cap, put the sticker back in place, reinstall the fan and test it.

Sometimes this will make things better, but if it doesn't then it is only fair to replace the fan.

regards

Triarcuate

Sep 25, 2009 | Marshall Mg100dfx 100-Watt Combo Guitar...

2 Answers

Seems to be a noisy fan on mb4210 combo


Could very well be the fan. The motors can cause interference. There may be a solution to get rid of the noise. Some copper shielding tape may help. You could rule out it being a microphonic preamp tube by turning the amp on as normal and tapping the tubes with something non-conductive. If you hear the tapping noise coming thru the speakers while doing this to a particular tube, replace it. With power tubes, the tops of them turn white on the top when they become microphonic, along with plenty background noise.

Apr 18, 2009 | Marshall Music

1 Answer

I have a Marshall MG50DFX. It's about 2 years old. I took it out on a gig and it quit working. The fan still works, but no sound. This amp is practically brand new. I am very diassappointed with the...


Hi a couple of years back I had a similar problem. Remove the chassis, you will see a wire (might be blue) it is quite noticeable (looks like a jumper a few inches long). It controls channel switching. Check it for dry solder or broken at either end. Good luck, Dereeldeel

Jan 16, 2009 | Marshall Mg50dfx 50-Watt Combo Guitar...

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