Don't calibrate a broken meter!
The way the voltage reference system works on this is a little convoluted to understand and the hand-drawn schematics have a few rough spots in my version, but I would guess your problem is in the vicinity of VR1/R11/U18/U19/U20/U8A and the resistor divider near VR1. Definitely check as many ranges as you can at two or three points within each range, just to make sure the fault is consistent and linear. I had a small pile of these and similar meters. I ended up fixing two or three of them then decided the rest just weren't worth the effort. You will learn something in any case.
You should test the power supplies and so on, but I wouldn't go replacing anything yet unless you observe a fault. Depending on the results you get from testing all the ranges, you might look at the jumper selection process for when there isn't enough room on the calibration pots. You also can check the voltage and current of VR1--this will require desoldering and lifting a leg, but it will tell you a lot about what is going on.