I know this question is old but I needed the answer and it wasn't here, so now I'm sharing. This is a two man job that can be done in less than an hour with a 1" Wrench and a screwdriver (our access panel had two flat-head screws on it, though they were very tight after eight years).
HOW TO ADJUST THE SELF/AUTO LEVELING SYSTEM ON A TEREX HI-RANGER 52 BOOM/BUCKET
I just bought a 98 Asplundh truck that ended up out of alignment. The bucket on the end of the boom would no longer self level (though it would adjust as the booms were moved, the bucket itself was about 15 degrees off). We have a Terex Hi-Ranger 52' boom (adjusting an Altec boom is much different from what I understand).
To change the alignment on a Terex boom, you have to open the leather flap at the bottom of the boom (where it articulates or rotates at the base or truck body). Also open the access panel on the side of that area (it's about six inches round with a screw on each side). In that access panel there is a tensioner for the cables. Loosen the tensioner until you can move the chain around the end of the sprocket. No have someone keep the bucket level and pull the chain as tight as you can around the bottom of the sprocket and wrap it around to the top, then tighten the tensioner. Close everything up and you should be done. Best of luck!