Took the F-75 out today and found 2 quarters, 2 dimes, 2 nickels and 12 pennies(one wheat). One question....My display sometimes goes blank, except for the battery level. Is that normal? Is it because there no targets or does it skip targets? If I wave my digging tool by the coil it immediately reads it. If I'm in a trashy area the machine keeps on reading/ displays targets.