I suggest one should not vary the switches on coil taps or vary the roller
inductor with power applied!
Instead, pick a setting; make a low power transmission checking the SWR,
unkey, then try another adjustment either side of the one, to see if that
reduces the SWR. Don't turn the switch or roller while keyed down!
Keeping power on while roller inductor is varied or while the switched
inductor tap is varied arcs the contact, and burns it until it needs
replacing. I have a 300 watt basket case transmatch that someone burned the
wafer switched inductor contacts on, sitting on the bench now for repair.
Lucky I keep spare wafers for many types of switches. They had also left
the thing in line and gotten a surge that wiped out the diodes in the SWR
meter. Probably when they were not operating.
Always disconnect your antennas from rigs when you are not in the shack and
using them! Ground the antenna leads for safety.