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]

Check send/return jacks for dry joints or contact contamination