Service Manual for a Beckman 320 Digital Meter

[spearthrower]

HI all! Does anyone have, or know where I can get, a service manual for a Beckman 320 (300 series) digital meter? I already have a user manual, but need to troubleshoot a problem where the meter does not "zero" on any of the AC or DC voltage ranges, or on the resistance ranges when the probes are shorted. The display simply flashes random values endlessly, and does not zero. Thanks for your help!!!