SRK Electronics FMA501, Manual, Page: 23 / 33

SRK Electronics FMA501 manual
 2007 SRK Electronics Pty Ltd 22
7 Trouble shooting
7.1
Diagnostics
Due to the extensive metering provided by the FMA501, diagnosing a failure becomes much
simpler.
Failure of the amplifier will generally result in a full or partial loss of output power. Careful
interpretation of the various parameters will generally indicate the likely cause of the problem.
For example, in the case of total loss of output power, the following routine should be used:
Does the LCD light and allow parameters to be measured? If not then suspect the control
board. Look for the presence of +15V, +5V and -9V power supply voltages.
Does the amplifier DC voltage read correctly. If not, suspect the main PSU.
Is there any RF input power shown as present? If not then the problem lies external to the
amplifier.
Do the amplifier A and amplifier B currents measure as normal? If not then suspect Q1 or Q2
on the amplifier palette.
Partial RF failure should be investigated in a similar manner, paying particular attention to
input power and the relative values of the amplifier DC currents. As a guide, these two
currents should be within 20% of each other. If not, suspect the transistor with the lower
current.
7.2
Disassembly
Commence by removing the IEC plug and all other external connections to the FMA501. This
is to ensure the safety of those undertaking the disassembly.
Remove the screws holding the upper lid and remove lid.
Remove all connections between the amplifier palette and the control board.
Remove the three cables between the amplifier palette and the output directional coupler.
Disconnect the red and black wires from the amplifier palette by pulling off the QC
connectors.
Disconnect the BNC plug on the input RF connector connected to the palette.
Turn the amplifier over and remove all the screws holding the lower lid.
Gently lift the lid, bringing the amplifier palette with it.
If needed, remove the 6 screws holding the amplifier palette to the lower lid.
To remove the control board, remove the two screws holding the protective cover in place.
Disconnect all connectors to the control board.