Hello I would like to inform you I'm a technician and I have a problem with Marshall guitar amplifier : valve state model 8100,some intergreted circuits where remouved.just if you display for me the circuit board I will be able to repair the amp,please help me and i would like to inform you again that I repaired so many Marshall amps alredy, please help me thank you.

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 [email protected].

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'!

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

Read your manuals for both pieces of gear carefully first. You only have one amp so you won't be able to take advantage of all the FX on the Digitech as a lot of them are designed for stereo. The Digitech manual shows guitar into the Digitech and output from the Digitech into input of any guitar amp. Since you have a Marshall and can already get some great sounds by running your guitar straight into the Marshalls input, you would probably be better off using your Digitech in the FX loop. Run a guitar cord out of the send on the loop into the input of the Digitech and a guitar cord out of the left / mono output jack on the Digitech into the effects return jack on the Marshall. Start out with the effects level on the Marshall all the way down. Do the same with the Digitech with both the input and output levels. (Read the manual carefully) I think the choice of the Digitech isn't that great because it is already trying to reproduce a lot of what you can already get with just your Marshall but with a little experimentation and some careful adjustments you should be able to add to the sound of the Marshall. Hope this helps.

I may be missing something but i cant see what amp you have? Is it a valve or solid state marshall?

Well i know ive destroyed a guitar amp with a bass guitar before :-p this is why they make bass amps and guitar amps instead of just amps

Best thing is to open the unit and extract the fan and find the EXACT model number fan online and replace it. There are only two wires to solder., but mechanically these can be a mess to get to.

Hello endaya try www.digikey.com if you are using a 2amp buss fuse, its available, 117V is applicable to 220V, just follow the amp rating.

if this a tube amp then your tubes might be going bad. but if it is a solid state amp then im not to sure whats going on.

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.