I have a vintage White's 6000/di series 3 metal detector. It's been working fine for years. Last year we replaced the switch that changes the mode on the handle. After the switch was replaced it worked great. This year the meter needle does not move in the GEB Discriminate mode. It does not identify the target...penny, dime, quarter ect. The needle should lock on to the target until you release it using the mode change switch. The detector will work in the GEB Disc. mode but the meter does not. We have checked all the meter connection and everything looks good. Any suggestions or advise to solve this issue? Thanks.