Question about Marshall Mg15dfx 15-Watt Combo Guitar Amplifier

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Basically, I turned it on, played it, turned if off, went back to play it and I got a humming noise then it went dead!!??

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I suspect either the power supply rectifier developed a short which would likely blow a fuse till repaired OR the power amplifier chio went bad. Most of the smaller amps use some version of the TDA2050 audio amp chip. It looks like a power tab transistor (TO220 stylle case) with 7 leads.

If it went, it did so for a reason... time for unit to be serviced.

Posted on May 27, 2010

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I have a Crate CR212 it started to hum/buzz today. It would not play out any sounds other than the noise. I unplugged everything and still it hummed. I unplugged the unit, check the fuse and replugged and...


Are all the tubes lighting up? they should glow like dim light bulbs. If not, replace them with the same model type (12ax7, or EL34 for example).

Often there are two fuses, one to protect the speaker and another to protect everything, it sounds like the latter fuse may be burned out. take it out and take it to radio Shack for exact replacement.

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My sc40r amp started humming really loud after i had turned it on... it played perfect the night before... but when i went to go play it this morning it started humming really loud then stopped and began...


You take it in for electronic repair. Unless you are electronically adept at troubleshooting and repair this is not DIY. Probably one side of the PA transistors has shorted. You can blow the speaker if you keep trying to use it this way.

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This is on a 15 watt Peavey Vypyr. I have a buzzing at the bottom end of my amp, when playing on the low E string. I plugged in my headphones and the buzzing went away while playing. I have also raised my...


The voice coil on the cube speakers must be scraping against the magnet.Or the speaker cone must be damaged causing it to flutter at low frequency where there will be large cone movement. Try removing the phono jack from your musical instrument/ guitar and touch the tip of the jack with your finger. You will hear a hum, now turn down the volume and listen to the speakers very closely and see if you can identify the flutter. All the same you will have to fix the speaker or replace it. Have you ever dropped the speakers, if so the speaker frame could have warped causing the scraping noise.

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My Marshall Haze 40 Amp started making a very loud humming noise after a couple hours of playing.I let it cool down,and turned it back on and the noise came back after a few minutes


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

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The amp plays fine for about 15 to 20 minutes, then an extremely loud, over powering hum/buzz takes over, and then the amp has to be turned off, but the problem persists. I've tried several guitars,...


You say the "tubes are fine" I take it that you have either replaced them with new or used a very sophisticated tester on them. A heater-cathode short might cause the symptom. There are a bunch of tests I would want you to run alnd get back to me with the results.

Heat up the amp but DO NOT play anything into it for the usual failure time or more and they start to play i... did hum occur WITHOUT playing? With all volume controls down does the hum occur?

The right tools is an oscilloscpe to fing out if the filter caps are good. These are C31, C33, C35, C36.

With hum present in failed stater, plug in a grounded plug into the power amp in jack... if hum is stiil there, check the +/- 16 volts regulating Zener for ripple. get schematic here:

http://elektrotanya.com/fender_hot-rod-deluxe_sch.pdf/download.html

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Of course it is repairable.

Find a competent repair person. You did not describe the "noise". If it is 60 cycle hum, the filter caps need replacing. If it is an organ tone, then probably a key contact is stuck.

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try connecting speakers to another sound source or if you have access to a ohm meter, check impedance of speakers, should measure 4~8 ohms.

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