Question about Marshall MG100HDFX 100-Watt Amplifier Head

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My mg 100fx has a scratchy pot in the master volume, i have the face pate out and have sprayed the master very carefully. the problem is still there?

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What did you spray it with? I hope NOT Deoxit or Blue shower as those wreck the pots by removing the lube.

Use CRC226 available in the electrical dept at Home Depot. Use the plastic tube by bending it so it can spray upward into the slot where the leads that solder into the board go into the metal can.

Spray a little in and work the pot... then try a little more and see if it improves the situation. If it does, treat all the pots the same. ALSO look for broken solder where the pot wires solder to the circuit board..

Posted on Mar 15, 2011


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Samic guitar amp LA30R. How do I repair the volume control?

First you need to get access to the hardware. Disconnect the speaker wires from the speaker, then unscrew the 4 screws located on the top of the cabinet (one in each corner near the corner guards). Once that is done you should be able to slide the electronics out of the cabinet. How you fix the volume knob really depends on what is wrong with it. If it is scratchy and sporadically responsive, it might just need a good cleaning, which is easy. Otherwise it might need to be replaced, which is less easy, but still easy enough if you are handy.

To clean the knob, you will need to get some electrical contact cleaner (I use Deoxit, but anything designated for this task is good...I wouldn't use WD-40). I remove the potentiometer from the face plate, but you can likely clean it without removing it if you can get at it. Set the nozzle against the tiny hole by the back of the pot and give it a quick spray, then rotate the knob back and forth a bunch of times (like 40). Voila. While you are there, clean all of the pots, as a preventative if nothing else.

If you need to replace the pot, things can get a bit trickier. If you are handy with a soldering iron, desolder the contacts on the back of the pot and replace it with the same type of pot (you can cut it out too, but that gets messy). Take note of any markings on the pot. It will likely say something like A500K...the first letter defines the type of pot (audio vs linear), and the number defines the resistance (500K, in this case). Getting the wrong pot in there can drastically change what you get out of your amp, and probably not in a good way. Solder your new pot in place, then put it all back together.

Make sure you test the amp once you have cleaned/replaced the pot before you screw everything back into place. Hook the speaker back up, power it up, and see what happens. If everything is good, lock it down. If it still isn't working, you may have a bigger issue than the pot, and you should likely take it in to a professional. Good luck!

Aug 29, 2015 | AMP Music


Electronics spray cleaner

The most common problem with guitar amplifiers

and other electronics that are making noise or cutting out

or sticking and not working correctly is a simple fix...

I use Radio Shack electronics spray contact cleaner

for most of my basic repairs

in the pictures posted I show the basics you need....

some screw drivers, basic knowledge, paper towels,

electronics spray contact cleaner, and a knife

First I carefully remove the nobs (volume control, tone control, etc...)

I use napkins to mask the area and keep from scratching the surface

Then I carefully spray into the (control} and work in back and forth....

the Best way is to spray directly into the potentiometer

that requires access to the internal chassis

on a quality pot there is a Notch that you want to spray into

on a standard pot just spray....

this will repair any scratchy noise or sound that cuts out

on guitar and bass amplifiers,

also can be applied to many other common basic sound problems

I hope this helps someone out?

i could Not upload photos? so please check My link....

on Mar 13, 2015 | Music

1 Answer

Master volume is scratchy on MG100FX

All i can suggest is to use electrical contact cleaner on it from the inside. But you,ve already done that. And i would imagine that the master volumes will be the same to, Harry

Dec 28, 2013 | Marshall Music

1 Answer

How to clean volume pot on a rmx5050

Just spray a few shots but you have to take the top cover apart, then take out 3 philips screws in the pots module, take off caps and then you should be able to give'em a good cleaning spray shots.

Feb 11, 2013 | QSC RMX 5050 5,000 Watt Power Amp

1 Answer

Slide pots for PV14 mixer

The pot needs to be cleaned. Get a spraty can of DeOxit 5. Spray it into the track and move the slider up and down a number of times. If that doesn't fix it, replace the slide pot.

Jul 30, 2012 | Peavey Electronics Peavey 00512140 PV 14...

2 Answers

The volume control on my Gorilla GB-30 amplifier crackles when turned, but the actual volume never changes. Will a new control switch fix the problem? Are manuals available?

There likely is another problem, possibly a cracked circuit board or bad solder at the control. If the control worked at all, there would be some change in volume. Take unit in for repair.

Feb 08, 2011 | Music

1 Answer

Replacing the volume pot on a Gibson ES335.The best method for getting the old pot out of the guitar to enable it to be unsoldered and the new item to be soldered in it's place and put back into the...

If the volume pot is scratchy noisy, FIRST try squirting a bit of CRC226 into the pot. CRC226 is available at Home Depot in the electrical department. There are other CRC products there so be sure to get the 226 type. About $2.75 a can.

The product is also good to use in slide pots on mixers. Use sparingly, it doesn't take much. For rotary pots you often can use the spout to spray into the slot where the terminals go into the pot.

Sep 20, 2010 | Gibson Es345 Reissue Vintage

2 Answers

Scratchy volume potentiometer

Try cleaning your volume potentiomenter with contact cleaner (they come in spray can's), the scratchy sound is audible when you turn your volume control on, the contacts inside your potentiometer accumulated dust or some other particles.

Aug 11, 2010 | Alesis Sr 16 Stereo Drum Machine

1 Answer

Thomas jester 132 organ troubleshooting E-flat below mid c not working correctly on either keyboard or foot pedal all other keys ok volume pedal is scratchy but works ok

Here is where you can get the service manual: Since the problem is with the foot pedal note and the keyboard note I would suspect that there is a problem with the tone generation circuit for that note. You might try cleaning the key contacts on both for that note first to see if that works. The volume pedal probably just needs the volume pot cleaned with contact cleaner spray. I hope this helps. Let me know if it does.

Nov 26, 2009 | Music

1 Answer

What causes the static background noise in my keyboard?


It sounds as though you have a static electricity problem in your volume pot. Although there are sprays on the market that you can use for all of the electrical switches on your keyboard which removes and suppresses static electricity, one way to make sure this is the problem is to slide your volume slider to maximum, then minimum, up and down about 10 to 20 times, if the scratchy sound begins to diminish, you knwo the problem lies there. As a matter of fact, if you do it long enough, the sound may go away altogether, although without a good spray of electronics cleaner or electrical contact cleaner (which you can find at stores like home depot or online, even eBay), the sound will return.

If this is not the case, and the scratchy static sound does not go away or depreciate, it could be your cords or even static on the pc board inside the unit. If you are confident that you can crack the case on your board without causign damage, then get a screwdriver and open the case (all screws are located on teh bottom of the unit) and give it a good spraying with electrical contact cleaner on all of the contacts and even a once over on all of the circuit boards. Do not wet the circuit boards with too much spray, rather, give them a light misting.

For areas where you plug in, like your 1/4 inputs, your midi ins and outs, and headphone jack, spray the contact cleaner inside the holes. You don't have to worry about spraying too much in these areas. Just do not oversaturate.

Hope this helps, and thanks for using FixYa

Jul 18, 2009 | Music

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