We can not work on unsafe amplifiers. they can not be plugged in or checked if unsafe conditions are found.
We can not be unnecessarily endangered by the process of repairing an already dangerous electronic device.
Unsafe conditions: Frayed worn, cracked, power cords. Power cords with the ground lug (3rd prong) cut off.
these power cords will have to be replaced prior to any work or for any work at all. The general cost of this is $24.00 for the new cord and installation on a normal amp. It can be more on odd amplfiers.
Incorrectly wired amplifiers. Most common is reversed Neutral and hot - this is a death trap and can not be plugged in without being repaired/rewired correctly prior to any work. There are other unsafe conditions that can exist that must be fixed.
Wire nuts: they can not be used in guitar/bass/PA amplifiers and must be replaced with properly soldered and insulated connections.
Wire nuts making the ground connection are especially dangerous as they can come loose causing the ground to drift or, if a short occurs, to have a loose hot wire in the amp.
All of these conditions have to be repaired prior to and above any other work on the amplifier.