Question about Marshall Mg100dfx 100-Watt Combo Guitar Amplifier

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The RW5W in the R-15 spot on the circuit board of my marshall mg100dfx amp is loose and needs to be repaired. looks like i have to pretty much disconnect all front knobs and most wire connections, to pull the board just to flip it over and make quick solder? that sound about right? jack of many and master of few but looks basic enuf to me. any helpful hints appreciated

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  • Marshall Master
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Yes, they are a pain to have to remove the knobs etc. to get the board out.

If the resistor has burned or browned the board, resoldering may not be good enough as the traces to the pads and the pad MAY have unbonded from the board. In this case you may need to install eyelets to get adequate support for the resistor. The other method is to install "turret" terminals and attach the resistor to those... the turret terminals kind of rivet into the board to create a secure mechanical connection.

Posted on Sep 14, 2010

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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...

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Marshall MG15DFX - Sound cuts out randomly when using distortion or effects. Turning amp off then on solves it only until it happens again. Does not seem to affect the clean channel. Could it possibly be...


There are many things it could be... I often quote the probabilities based on many ears experience and the symptoms the person posts.

Based on what you have posted, there is an intermittent... the unit vibrates while operating... there could be a loose connection, however my guess is you will find bad soldering at one of the pots that control the distortion. The solder often breaks loose as the sometimes support the circuit board from the leads of these pots. Also switches that solder to the board and sometimes jacks for foot switches break loose.

Open the unit and inspect the solder joints. It often takes an experienced eye to spot the tiny grey ring around the solder meniscus that signals a failure.

Mar 11, 2011 | Marshall Mg15dfx 15-Watt Combo Guitar...

1 Answer

I was given a Marshall MG Series 15 DXF guitar amp. The input jack has been twisted off and broken out of the circuit board. I would like a diagram of this part of the circuit. OR Is this soldered to...


Typically these input jacks have 3 or 4 "tails" that solder to the circuit board. The best thing is to get an exact matching jack. You can search for 1/4 inch jacks with matching profile at Digikey.com, Mouser.com, and try www.tubesandmore.com/

In the future ALWAYS loop the guitar cord through the handle so plug is not yanked sideways when people trip over the cord.

Dec 14, 2010 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

I am look for a fuses for a Marshall amp like Mg100dfx


Radio Shack Has bus fuses. I don't work for them. The Shack is wack, but they have fuses

Dec 10, 2010 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

I need the schematics for a Marshall MG-10KK guitar amplifier in order to repair it! I'm a good technician but I don't speak english very well... rsrs Thanks!


Most of the problems with the small guitar amps are blown power amp chips. They usually use chips like the TDA2030 which look like a power transistor.
Most other problems involve broken connectors, bad solder joints or cracked circuit boards. The power supply area is so simple one doesn't need a schematic for that part which is usually just three terminal regulators for +/-15 volts. Schematics are often hard to find.
Try this site, although this is a different model, much of the schematic will likely be the same.

http://elektrotanya.com/marshall_valvestate10_10w_8001_8010.pdf/download.html

Nov 17, 2010 | Marshall 15 Watt Guitar Amp

1 Answer

Could I gut this Amp and MAke it Tube?


Maybe. The cost involved wouldn't reward you enough. Here are some links for you:http://www.drtube.com/marshall.htm and http://duncanamps.com/index.htm and http://www.ampix.org/ If you have all the tools, parts, schematics and above all experience. You may end up with something you like. Personally I would look for a vintage Marshall that needs a rebuild and start there. You will end up with a great amp and the experience you need to mod the MG100DFX if you really want to do it. Hope this helps.

Oct 21, 2010 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

Where can I get a schematic of the circuit board for the MG100DFX. The main fuse as blown and I need information on wiring connection to the transformer and values of other components.


Just a hint to troubleshoot: Connect a 100 Watt light bulb in series with the hot side of the power line into the amp. Make a cord with a light socket and a receptacle to plug the amp into. This acts as a resetable fuse and will send enough current through the amp to not fry stuff, but enough to do troubleshooting.

Apr 01, 2010 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

The gain control no longer works on the clean/crunch channel. all other features work fine, whats wrong with my amp?


Hi there. Try re-soldering the control pot to circuit board connections. If not, use ohm meter to verify pot functionality. If bad, replace.
Thanks
Paul

Jul 10, 2009 | Marshall Mg100dfx 100-Watt Combo Guitar...

1 Answer

Marshall MG100DFX noisy


Before you bring this into a shop, try spraying out all of the controls. Use an electronics switch cleaner that contains a lubricant. Spray into the control and work the control back and forth a number of times to loosen up any dirt inside. Then spray it again.

Let me know if that resolves the problem.

Thanks,
Dan

Feb 14, 2009 | Marshall Mg100dfx 100-Watt Combo Guitar...

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