Height of turntable in CDM1

Hi all.
I'm going mad with a problem.
No, with a solution.
Anyway: i have a cdm1 that don't read toc.
If i push play without a disc inside, the display says ERROR.
When i put disc in, the player don't read TOC.
If i turn a bit clockwise the screw 51 on the motorshaft, the player become normal, and read ALL. CD, CDR, hot dog.. :).etc..

So my question is, please:
What kind of problem its solved turning clockwise the screw 51, ie, increasing the space between laser and disc surface? Where is problem?

And, please, how i could adjust the tension , 0V, across R3240, in servo 1 board, every time i set a new height of the turntable?
Stephen, thank you for your kind attention.
i'm agree with you, obviously. This could be a normal fact.
but i think this is not my situation..
As you could imagine, when i start to turn a pot or a screw, as now, i mark with a pen the start position and the final one's.
So my surprise was great, when CDp falls to read toc again, and the screw 51 is it's right position. I don't have a oscillposcope, so i cannot see where the chhnge start in electronic...