There is not much between the LNB and the tuner in the DAC to prevent one form seeing a rise in AGC, even when on the wrong satellite, so if no change is seen, the dish is not pointing in the right direction, or there is an obstruction between the antenna and the satellite.
This could be for several reasons including:
Heading input is incorrect, Azimuth out of alignment, GPS position is wrong, Elevation is out of alignment, Polarization is on opposite pol, Satellite is blocked. Satellite frequency is wrong, Satellite longitude is wrong. Other satellite settings are wrong.
An AGC below 0400 or thereabouts, indicates that the LNB has no supply voltage, or the tuner has no connection to the LNB. Having said this, there are some tuner models that have and AGC of about 800 with no signal or supply voltage.
The following is an example of settings on Telstar T11n with a quad LNB. Your required settings may be quite different.
Manually checking the heading.
Press the left arrow and move the cursor under the heading, and then the up or down keys to change one of the digits to something else, and press ENTER. If the heading remains at the new setting and does not revert back to the original heading, then you are not receiving input from the gyro. If it changes back to the original setting, you are receiving data from the gyro.
Go to the bridge and verify the actual heading using a magnetic or hand bearing compass, taking magnetic variation and deviation into account. If the actual heading from the gyro is obviously wrong, you will need to correct this. If it cannot be corrected immediately, one can drive the antenna manually to the corrected azimuth to find the satellite. This will work for a while if the vessel is on a steady course or tied to the dock.
If it cannot be corrected, there are ways to disconnect the heading input and enter the correct heading manually to find the satellite. The antenna will need to be put into Sat Reference mode to operate without heading input until the gyro can be corrected.
Target the satellite again, as detailed above, and note the target azimuth and elevation once the antenna settles down. In the AZ EL menu, press the left arrow to slowly move the azimuth down about 10 degrees, while watching for changes in the AGC. Then try going up in Azimuth with the right arrow until you are 10 degrees above the target azimuth and watch the AGC. Return to the target azimuth. Then try using the up and down arrows to go up and down 10 degrees in elevation while watching the AGC.
Stop if you see a rise in AGC, and try peaking up the signal using the left/right and up/down arrows. Once tracking, check the receive light on the modem. If you get a solid receive light you can be 99.9% sure that you are on the right satellite. If not, you may be tracking the wrong satellite.
If swinging at anchor, you may need some assistance, communicating by VHF radio or cellular phone to ensure that the azimuth remains the same as the heading while observing the antenna in the radome.
The TV antenna receives it's power from the antenna controller on the coax cable, so turning off the antenna controller will reset power to both.
The level cage is a small, 50mm x 70mm silver or gold box on the side of the antenna frame that is driven by a small stepper motor with belt. When the antenna is first turned on, you will hear and see the level cage drive to it's physical endstop. When it reaches the endstop you will hear it cluck several times as it verifies that it has arrived at it's starting point. It will then move to the 45 degree position, and the antenna will drive in elevation to 45 degrees where the level cage should be level.
After a few seconds, the cross level will drive to make the antenna level from side to side.
The azimuth will then drive the whole antenna in a clockwise direction until it is pointing at the bow. After a minute or two, it will then drive to target the satellite. (TV antennas are different)
Watching the antenna as it initializes can often show up problems, especially with finding the satellite.