Although they are among the most recognised and reliable brands in the world, Marshall's amplifiers are still vulnerable to damage and breakdowns. But repairing them usually requires professional expertise, and the London-based Marshall says it won't sell to the general public any parts that require opening the amplifiers to reach. That means the best way to get repairs done is to contact Marshall or an amplifier dealer.
Check to see whether your amplifier is still under warranty. If it is and you live in the United Kingdom, call 01908 375411 to arrange a collection free of charge via Marshall's returns department. If you live elsewhere, contact your local Marshall distributor. Search for your local distributor worldwide at marshallamps.com/dealer/dealer_search.asp.
Browse telephone directories for local amplifier dealers, assuming that your warranty has expired. For an agreed upon price, they will deal with your amplifier's problem or help you acquire and install new parts.
Ignore amateur advice that suggests you open up the amplifier and use your own initiative to solve the problem. Without previous experience this can lead to even further damage to the amplifier. Furthermore, because of health and safety regulations, Marshall's website says the company is unable to supply "electronic parts or parts that require any form of disassembly of the unit to the general public."
Use a vaccum attachment or canned air and a spray cleaner and cloth to remove dust and debris from the unit. This is one piece of maintenance you can do yourself. Check your amplifier to make sure that the grille and screws are not loose, and tighten the screws if necessary.
Marshall's website says that "any work that involves removal of the chassis or back" should be "carried out by a qualified engineer only."