Common defects that cause fret/ string buzz are.
Truss rod adjustment.
Loose frets, caused by the fingerboard drying out.
Heavy fret wear causes string buzz.
Using a capo chews up frets fast.
Worn string slots in string nut or incorrect nut mounting.
Incorrect bridge saddle radius.
Neck angle/ tilt (bolt on necks).
Twisted, humped or warped necks will cause fret buzz.
Throughout the years many Nut & Bridge making materials have been used, all with their own unique tonal characteristics.
Some of the more highly sought after materials are Organic such as Fossilized Walrus Ivory, Mastadon Ivory, Bone and Deer antler to name a few. Pictured is a fang from a Walrus that lived over a thousand years ago. It is the preferred material I use as an upgrade for Bone, Micarta & Graphite.
Better sustain, tone and durability than other organic materials and warmer sounding than 'Micarta 'or 'Tusq'.
Remember, only Fossilized Ivory is legal Ivory.
Tubes lose their tonal quality long before they actually burn out.
Signs your tubes are weak include noisy operation (crackling/ popping), loss of power and or loss of EQ.
Proper Bias adjustment and ventilation prolongs the life of your tubes and gives optimum performance.
Scratchy or noisy faders and pots are the most common issue.
Jacks and other receptacles are next on the list.
Some digital effects issues can be as simple as changing out a PC board
Most problems are broken or sticking keys, broken jacks and dirt.
Just as vulnerable to injury as any other instrument, your keyboard should have a padded zip case or hard shell case.
Defects arise from too much heat, continuous high output operation above the clipping level, and just plain old hooking it up wrong.
Dirt: Just like a vacuum cleaner, these high rpm fans drag in lots of dirt clogging the fan blades, heat sinks and the other components, resulting in excessive operating temps and component failure.