20 Most Recent Marshall Amplification Marshall MG250DFX 100W Guitar Combo Amplifier Questions & Answers

The switching is done electronically by an analog gate chip. On IC9, check if the signal on pin 8 changes with switching between clean and OD... This is the actual signal that changes the gate. If you don't see a change there of say 5 volts, then the problem is in the circuits that drive this gate. If the signal is there, then the problem is in the clean channel audio op amps or the components around them. Let me know the results of the test.

I have read that the problem is in the FX send/return jacks which oxidize if not used much. All you have to do, apparently, is ram a jack plug in and out a bunch of times. This breaks up the oxidation, and allows the amp to work properly again.

IF this is a vacuum tube unit, these symptoms are that of a tube that the heater is intermittent, that is it cools off due to a break and then liights again.

Open the back and observe the heaters in the tubes. DO NOT be fooled by some that have TWO heaters in them. (use a mirror if necessary) A single one that comes and goes can cause the problem and the voiration can make it come and go. This behavior in a tube is NOT somthing readily spotted in a tube checker. The delay in fading and coming back would be the delay in warm up following a heater going out and cooling.

I rather suspect IC1 TDA7293 is the cause of your problem. If this is the case you will need to check the speaker/s

The fan will have a manufacturer's part and name on it.

Shop Digikey.com or Mouser.com for identical device.

Note that SOME amps have the fan throttled depending on temp and these fans get noisey when throttled down.
Not sure about your Marshall on. The usual fan failure is bearings get dry and coke the lubricant.

DO NOT FACE THE GUITAR TOWARDS YOUR AMP. IT WILL MAKE IT SQUEAL.

If you have no experience with amp repairs you are better off having it serviced. This problem seems to be related to bad solder joints in the FDD circuit exacerbated by the cooling fan aging and wearing out. Namely R107 and R96.

According to the schematic, once the signal is initially amplified (also where the LED shows signal), the audio is sent to the send/return jacks (shown on pg3-C7). A quick test to see if audio exists at the insert point will require an insert cable. An insert cable can be a balanced 1/4" cable which splits out to two mono 1/4" connectors or a pair of RCA's. Connect one of the insert outputs to a console (if 1/4" cable) or a tape loop on a home stereo receiver (if send cable splits out to RCA's) and see if you've got sound when playing your guitar (with LED on the Marshall showing signal). If no sound, go to (A) below. If you have sound, go to (B) below. (A) Ten pin connector labelled CON2 (shown on pg5-B1). Make sure connector is tightly seated and that the pins on the jack and the female connectors in the plug are clean and that good contact is being made. (B) Twelve pin connector labelled CON1 (shown on pg5-B4). This is the DFX board - make sure this is tight and well seated.According to the schematic there are voltages seen at several of the connection points previously mentioned. If you have a multimeter and are qualified and careful - check to make sure the voltages are present as shown. If you're not qualified - meaning you have little or no experience - STOP and refer this repair to a qualified bench tech. They get paid to keep the magic smoke inside the amplifier. You may end up damaging things worse or even beyond repair or even damaging yourself.

NOT SURE WHAT FLUG MEANS? IF YOU MEAN PLUG. CALL GHOST BUSTERS.

Since you just purchased this, verify that your guitar and cables are good on another amp and if they are good, then exercise your warranty on the Marshall.

Connectors and cables for guitars are chronic problems so verify they are good to avoid looking foolish.

This sounds like a thermal problem. You can often find the component by spraying suspected ones with circuit cooler, looking for a change.

you see that your amplifier's on off switch is push to on/push to off type. what came out of the amplifier is the knob which is pushes the actual switch. try to fix that knob from out side. if you are not able to fix it, put a plastic pen into that hole & try to push the switch. by this way you can put on your amplifier.

Best to replace the switch. There are likely one or two springs as well which may be lost.

Well without testing a bunch of parts. I would say some component in the clean preamp has changed. It may have happened over time and now you are noticeing it. without checking all the parts it would be hard to tell. Get it to a service center. Or you may send it in to Pro Line Music
215-736-8055

Open the unit and see if the wires to the speaker MIGHT be loose or making poor contact. The echo MAY be just the response of the speaker to the working one.