Amplifier Research 75A250A 매뉴얼 - 페이지 19

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Model 75A250A

4.3.5 Voltage/Amplifier Faults (Schematic Diagram Nos. 1011806)

The model 75A250A fault circuits sense voltage faults from PS1 (28V). They also sense an over

current fault in the final amplifier stage.

4.3.5.1

4.3.5.2

4.3.6 Low or No Power Output (DC Tests) (Schematic Diagram No. 1011806)

All indicators on the Model 75A250A VFD are normal, the VFD indicates "POWER ON" and

"STATUS OK," and the cooling fan (Blower B1) is operating.

4.3.6.1

4.3.6.2

Is the coaxial cable okay?

4.3.6.3

Feed-through Cap.

A3 C9

A1 C1

A2 C1

A2 C2

Note: The locations of the feed-through capacitors can be found on the RF Assembly

Drawing (Schematic Diagram No. 1010613).

Power Supply Faults (Schematic Diagram 1011806). PS1 sends a BUSS OK signal to

the operate/control board (A4). This signal gives an early indication of over voltage or

over current conditions. If either condition occurs the power supply sends a fault signal to

the operate/control board which in turn sends a disable signal to the power supply turning

off the outputs.

The Final Amplifier Assy Faults. (Schematic Diagram 1007872 and 1011806). The final

amplifier incorporates two stage protection for the output transistors. U1 monitors the

device current which is normally 6.0 amps. If the amplifier is over driven so that the

current rises to 8.0 amps U1 will decrease the bias voltage thereby decreasing the

current. If the amplifier is over driven to the point that the active bias cannot control the

current to less than 9.0 amps U4 will generate a fault signal which will turn the power

supplies off.

Check the RF input to the unit—is it the correct amplitude and frequency?

Check the RF output connection from the unit—is it correctly connected to the load?

Check the voltages at the following locations. Troubleshoot any incorrect voltages.

C12

Normal Voltage

+12V

-12V

+28V

Remarks

Gain Control

Driver Stage

Final Amp

Manual Text

4-5

REV A