Standard ST-337(Extech 380950) AC/DC Clamp MultiMeter Calibration

[andypandyplod]

Hi this is my first post. I have a Standard ST-337 Clampmeter,which is identical to an Extech 380950. I owned it from new, and have noticed from new the AC Amps range is reading approximately 10% low over the whole range. All the other ranges are fine. This meter uses a Hall Effect sensor for the current clamp.Inside there are 8 minature presets for calibation. Does anybody have a service manual, circuit,or know which preset does what adjustment?There are 2 presets next to the ribbon cable from the clamp,Iwonder what these are for?I have attached a picture of the PCB top showing the location of various components,and to aid identification-thank you