I have a 504 serial # I got in Dec. last year. I sent mine in a month ago for falsing and leaking. Got it back and the pinpoint and ground balance didn't work. How could they send out a repair and the pinpoint and the ground balance doesn't work. I was told they check them before they go out, so I guess something happened in shipping. Sent it back again. Tried it this weekend. I went to a spot I hunt regularly and didn't seem to be getting the signals I thought I should. I went over a big piece of metal laying on the top of the ground and could only pick it up at about 6 inches. Then I put a quater on the ground and could only pick up a signal at closer then 6 inches and only a good signal from about 5 inches or closer. My friend tried it with his ACE 250 and could pick it up at 8 or 9 inches. My ground balance ued to be 80 - 85 now it was 65. I keep seeing all the good results everyone is having with the updated units, but I'm really sick of fighting with this piece of junk. I put up with the falsing for 9 months, but at least I could make finds. Now it's quiet, but what good is it if it doesn't get any depth. I'll see what Garrettt has to say, but I'm really sorry I bought this thing.