Minelab F1A4 Service Manual page 9

2.2.3 Ground Balance Testing
Note: The F1A4 Control Box will memorise its last Ground Balance settings when
switched off and then on again. If a Control Box/Coil combination has been
previously balanced to the GB Test Piece, on re-testing, a response to that hot rock
will not be heard again. The same Control Box/Coil combination must be re-
balanced with a GB Test Piece with different characteristics before re-testing. (If a
suitable GB Test Piece is not available, a piece of ferrite or local ground around the
workshop may suffice.)
Note: For the first five seconds when the Off/Search/Balance switch is switched to
the Balance position, the F1A4 will ground balance at a fast rate, after this time the
F1A4 will continue to balance but at a much slower rate. Consequently, if the F1A4
has not completely balanced out the GB Test Piece within five seconds, release the
Off/Search/Balance switch to the Search position and reselect the Balance
position.
The F1A4 should initially detect the GB Test Piece (a change of threshold
tone will be heard) as the GB Test Piece is moved to and from the Coil. The F1A4
will then become "balanced" to it, i.e. the F1A4 threshold will remain stable as the
GB Test Piece is moved to and from the Coil. To confirm that the F1A4 has
'balanced' correctly:
1. Release the Off/Search/Balance switch so that it returns to the Search
position.
2. Move the GB Test Piece as described above and confirm that there is no
further response from the F1A4.
3. If a response is still heard, check that there is no metal on the technician or
the GB Test Piece and repeat the test. If the F1A4 still responds to the GB
Test Piece, the faulty Control Box or Coil, (Section 3.4) should be replaced or
the F1A4 should be sent to an accredited F1A4 Level 2 maintenance
workshop for repair.
F1A4 Field Service Manual – Level 1 Maintenance
While holding the Off/Search/Balance switch in the
Balance position, move the GB Test Piece up and down,
approximately 25 to 100 mm from the Coil.
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