ELECRAFT K4 - Page 127

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ER51, High LPA reflected power; check antenna: High SWR seen at
the 10 watt stage resulted in excessive reflected power. The antenna
may have changed, or you may need to do [ATU TUNE]. If the ATU is
off, hold [ATU] to turn it on.
ER52, High PA reflected power; check antenna: High SWR seen at the
100 watt stage resulted in excessive reflected power. The antenna
may have changed, or you may need to do [ATU TUNE]. If the ATU is
off, hold [ATU] to turn it on.
ER53, High LPA temperature; check LPA heat sink screws:
Temperature at 10 watt stage exceeded its limit. This could be caused
by the screws on the bottom cover becoming too lose, by high
ambient temperature, or by excessive key-down time.
ER54, High PA temperature; check fans: Temperature at 100 watt
stage exceeded its limit. This could be caused by inoperative rear-
panel fans, by high ambient temperature, or by excessive key-down
time.
ER55, High LPA current; check antenna: Current drawn by the 10
watt stage exceeded its limit. This may be caused by a sudden change
in antenna SWR. Adjust the antenna or use the ATU to obtain a better
match.
ER56, High PA current; check antenna: Current drawn by the 100
watt stage exceeded its limit. This may be caused by a sudden change
in antenna SWR. Adjust the antenna or use the ATU to obtain a better
match.
ER57, Invalid FSK data input selection: FSK keying via a serial I/O port
can only be done using the DTR control line, not RTS. Choose a
different signal for FSK (see Serial I/O menu entries).