I did a board change today and upon powering it up the display on the key meter is broken. the LCD backlight comes on, but the screen is blank. any ideas? also i completely forgot which way the tails go, so i just put them back in as i would do for a normal meter (never really had much to do with a key meter before) as they were no markings on the meter. I put them in L N N L, i did a polarity check at the top of the MS so i assume it's ok...?