Connect your instrument to the amplifier using an instrument cable. Lower the volume on your amplifier before powering it on. Slowly raise the volume and begin strumming your instrument until you hear sound produced from the amplifier.
Listen carefully to the sounds produced by your amplifier. If you hear a loud popping sound, this could be a sign of transistor failure. Remove the transistor tubes one at a time, starting at the preamp. If the popping stops after removing a transistor tube, replace that tube with a new tube. If the popping stops completely, the transistor tube you have removed is the source of your amplifier's failure.
Check your amplifier's fuses if your amplifier fails produce any sound. A blown fuse will inevitably cause amplifier failure. Although you must replace the fuse, blown fuses are always the result of another problem within the amplifier, such as a short in the wiring or power tube. After diagnosing fuse problems, take your amplifier to a repair technician for further analysis and repair.
Check your preamp tubes for any sign of damage or overuse if your amplifier is incapable of reaching higher volume levels. The procedure outlined in Step 2 is also applicable in this situation. If you need to replace a faulty tube and are unsure of the exact product you need to purchase, seek the advice of a technician at your local music shop.
Turn off any effects pedals you may be using to test your amp's ability to produce a clean tone. If the sound is distorted or muffled, this could be an indication of a torn speaker cone. As with any specialized repairs, having your amp professionally serviced will ensure that the problem is corrected.