Knowing how to quickly troubleshoot potential amplifier problems is an essential skill to develop if you are a musician. If the amp isn't able to produce the sound that it should, the solution may be as simple as plugging into a different power supply, replacing a bad cable or cord, or replacing a fuse or tube. Other cases may require more serious repairs, such as repairing or replacing a speaker.
Read the manual for your bass amplifier. Bass guitar amplifiers come in a variety of shapes and sizes. Most amplifier manuals contain a troubleshooting checklist.
Check the power supply to the amplifier. Make sure the bass amp is firmly plugged into a power source and the power source is turned on.
Double-check the volume and tone controls on the amplifier and on the bass guitar. It is not uncommon for a knob to be turned all the way off by accident. The volume knobs and tone knobs usually have to be turned to at least one or higher for the bass amp to produce sound. Plug a different guitar cable into the amp and guitar. A bad cable can produce scratchy, crackling sounds, intermittent sound or no so sound at all.
Inspect the fuses. Refer to the manual to identify the type of fuse(s) and the location of the fuse(s) in your bass amp. It may be necessary to remove a panel cover to access the fuses. Remove the fuse from the amplifier. If the fuse is blown, it will have a brownish, burnt appearance. Replace it with the appropriate fuse for the bass amp.
Examine the tubes if your bass amp is a tube amp. Weak or bad tubes can be responsible for amplifier problems ranging from no power, a weak or muddy sound, or a distorted sound. Properly functioning tubes have a warm, orange/yellowish glow. A bluish-purple glow means that the tube is weak and underpowered. An intense, reddish glow indicates that the tube is being overpowered. If the tube is not glowing, it is broken. Replace weak or broken tubes with the appropriate tubes. Turn off the amp and allow the tubes to cool down. Make sure each tube is connected tightly to the tube socket. Remove loose tubes and reinsert them to make a tighter fit.
Inspect the input jacks and input jack wires. Leave the amplifier in the off position. If the wires are loose, disconnected or frayed, they must be re-soldered to make a firm connection. Input jacks eventually become loose from overuse. Tighten loose input jacks with a wrench.
Clean the amplifier potentiometers, or pots, with contact cleaning spray. The pots on the amp need to be periodically cleaned because dirty ones can produce static-like noises and hissing noises. Spray the pots with contact spray and turn the knob back and forth to work the cleaning solution into them.
Examine the speakers. A bad speaker may produce no sound at all or it may produce a distorted or muddy sound. Remove the speakers from your cabinet if it's not possible to examine them without removing them, depending on the type of cabinet. Small rips or tears in speaker cones can be repaired with tape or glue. If the cone and coil have separated, the speaker must be replaced.
Keep spare fuses, tubes, and tools in your gig bag. Carefully read the manual for your bass amp so you understand how it works and how to treat it.