Z motor problem with powervault 130t

Greetings,

I've recently purchased a used PowerVault 130t.
Unfortunately I have a problem with it - after I turn it on and it starts going through the prelimary checks of the library mechanism, the following things happen:

- the arm / head gets rotated using the theta motor (no problems here)

- the arm / head gets lifted to the top of the library using the Z motor

- once reaching the top of the library it tries to keep going and makes a unplesant sound (and the rubber belt skips a few teeth) and stops after a few moments

- the arm / head is then lowered to the bottom of the library and makes a unplesant sound (and the rubber belt skips a few teeth) and stops after a few moments

- the service required light comes on and a message is show on the LCD: INOP = #308E, MECH = Z

in the FSC check menu I see the following errors:

308E Z 14

3106 NONE 13

3060 Z 11

309D NONE 79

To me it seems that the Z motor / mechanism isn't getting a signal that it has reached the top or bottom of library - does anyone know if there is a switch or similar mechanism that I could check?

Unfortunately, since it is a used device I don't have the documentation cd (with the FSC.txt file) so I can't check the codes...

Can anyone help me out on what I should check and what the codes mean?

thank you in advance for your help

regards,
Mike