Amplifiers have few mechanical components so generally suffer less from day to day wear. The most common issue with old amplifiers is a crackle coming from the speaker output when knobs are turned or button pressed. Most commonly the volume knob will suffer from this. This is usually just a dirty and dusty ‘pot’ (potentiometer) and can be remedied by spraying some contact/switch cleaner into the mechanism and turning the knob through its full extents many times (whilst the amp is off). You will probably have to remove the knob itself first and may need to open the case to access from behind.
The next common fault on an amp is a blown internal fuse, which can occur when the outputs have been shorted/overloaded or if there’s a fault. In this case the amp may light up (sometimes light up with a different colour LED) and not produce any output. If you’re lucky simply replacing this fuse will fix it, however if the new fuse also blows, there will be a more serious fault that will need to be looked at by a specialist.
Some amplifiers do produce a hum from their power supply transformer (coming from the amp itself, rather than the speakers), however excessive hum my point to a faulty transformer.