There is no sound
None of the sound from the guitar is amplified; no sound is coming from the amplifier
Faulty Power Connection
Check to make sure the power cord is not damaged. If the power cord is broken, you can take it to a repair shop or fix it yourself. Also make sure that the wall outlet you are using is functioning. You can test this with a phone charger or any other electrical appliance that you know to be working.
The sound is fuzzy, muddy, or unclear
Damaged Speaker Cone
Sound issues are almost always caused by a ripped speaker cone. In order to determine if this is the case, refer to the speaker replacement guide to see how to remove the speaker. Inspect the speaker for warping, rips, holes, or tears.
Amplifier Tube Issues
Remove the back panel and carefully reset all the tubes, following the same process as the tube replacement guide. Ensure that the tubes are glowing evenly when the amplifier is on. If a tube is not glowing properly, or there is a loose component in the tube, it is likely damaged and needs to be replaced. Replacement power tubes may be purchased here. Replacement preamp tubes (smaller tubes enclosed in metal covers) may be found here.
There are popping or clicking noises
Faulty 1/4 Inch Cable or Input Jack
Popping and clicking is usually the result of a faulty cable connection between your guitar and the amplifier. If the problem persists after swapping cables, the problem could be from a bad (1/4 inch) jack.
The grill is popping out or out of place
Improper Reassembly or Missing Screw
Check each mounting point for proper screw connections. If some of the screws are screwed in at a skewed angle, try removing it and screwing it back in with the correct alignment. If there is a missing screw, then remove an identical fit and bring it to a hardware store for an identical matching replacement.
There are rattling noises
Loose Object Inside Amplifier
Use a flashlight to look for any loose objects that may be vibrating when amplifier is on. You may want to rotate the amplifier to move around the dislodged object in order to ensure nothing else may be loose inside.
Mis-Set or Damaged Amplifier Tube
Check each vacuum tube for misalignment or damage. Individually remove each power vacuum tube from the amplifier and reset their connections several times. This will clean the contacts to the tubes. If necessary, you may repeat the process with the preamp vacuum tubes if necessary.
Damaged Solder Connection On Silicon Board
If you are still left with undesirable fuzziness, you should quickly check each solder point on the circuit board. Steps 1 and 2 of the input jack replacement guide show how to remove the circuit board. If you need to check the smaller circuit board that leads to the front knobs, look at steps 3 and 4 as well. If you detect a bad connection, take your amplifier to the repair shop.