Maintenance
10
2.
Inspect the coolant.
The coolant should be clear, with a faint yellow tinge, and have a slightly sweet smell. If it is black with a
burnt or acrid smell, drain it and add about 2.9 gal (11 L) of coolant.
With the load still on end, the coolant level should be 4
3
4
to 5 inches (125 mm) below the top surface of
the resistor assembly mounting ring, at ambient temperature.
3.
Add coolant if necessary
Repair
RF Connector
The Bird 8251 and 8251N have a special Bird “QC” connector which allows easy changing of the RF connector. This
does not disturb the coolant seal or affect the electrical continuity of the load. To change the connector, proceed as
follows:
1.
Remove the four screws at the corners of the RF connector.
2.
Pull the connector straight out.
3.
Push the new connector in.
4.
Ensure that the center pin on the connector is properly seated in the mating socket on the load.
5.
Replace the screws.
Note:
If not using the connector normally supplied, frequency and power must be limited to the capa-
bilities of the connector.
Rear Seal
If the coolant has not been drained from the load, stand the unit on end with the RF connector down before
disassembly.
1.
Unscrew the four screws at the corners of the guard cover.
2.
Unscrew the tube nut from the tank nozzle, using a small wrench if necessary, and pull the nozzle free.
3.
Unscrew and remove the clamping band.
4.
Remove the rear cover, including the attached escape tube and the diaphragm seal.
5.
Inspect the diaphragm seal and replace it if it is not pliable or has surface cracks.
CAUTION
Use only Bird coolant, P/N 5-1070, to prevent damage to the load.
WARNING
Disconnect the unit from all power sources before servicing. The unit may be energized
from multiple sources. The potential for electric shock exists.
WARNING
The vent plug must be used at all times when the unit is operating or cooling. Failure to do
so could result in an explosion or severe burns.
WARNING
Disconnect the unit from all power sources before servicing. The unit may be energized
from multiple sources. The potential for electric shock exists.
