3003 Axis lag exceeds 16mm

This alarm suggests a loss of control to one or more of the axes or the axis lag is incorrect. The usual causes are the loss of the tacho signal, faulty resolver balance resistors or a faulty motor. Check the 63 amp ceramic type fuses in the 'Bosch' drive unit. If any fuses have blown, replace all three and refer to paragraph (a).
a) If all the axes are in a safe position power-up the machine and note which axis, if any, runs out of control. If preferred, each axis can be checked individually by isolating the other axes. This is done by removing the 63amp ceramic type fuses from the axis drive units leaving in the three fuses for the axis required, X axis usually to the left. 
b) If, on powering-up the control none of the axes run away but one of them oscillates (monitor the lag display to check), the fault is likely to be associated with the precision 5ohm resistors mounted on the resolver terminal block. Check the condition and accuracy of these resistors (0.05%), and ensure that the terminal screws are tight, then go to paragraph (e). If the error only occurs at high feedrates, check the DC output voltage to the motor terminals C1 and D1 at a feedrate of F1000 and compare the result to the other axes. If the faulty axis voltage is significantly lower, the motor has probably de-magnetized and repair or replacement is required. If the output voltage is similar to the other axes refer to paragraph (c).
c) Switch off the control and transpose the 'Servo Output Boards' (SO 50x) situated in the lower rack at the rear of the control towards the right. Again power-up the machine, if the error transfers to a different axis there is a problem with one of the 'SO' boards and a replacement is required. The X & Y axes are controlled by the left-hand board as viewed from the rear. If the axis behaves as before, switch-off the machine and transpose the 'Speed Regulator' boards in the 'Bosch' Six-Pulse Drive Unit, and retry. If the fault transfers to a different axis, there is a problem with one of the 'SR' boards and a replacement is required. If the same axis is still at fault, switch off the control, return the 'SO' and 'SR' boards to their original positions and continue with paragraph (d).
d) The fault is likely to be the tacho mounted on the end of the motor. Either disconnect wiring and remove the motor for repair or work on the motor in situ. To gain access to the tacho the motor end cover, resolver, resolver mounting plate and flexible coupling must be removed. Remove the locknut or gear securing the tacho commutator. Check the condition of the tacho brushes ensuring correct contact with the commutator; if one of the brushes has broken contact, that is the cause of the error. Remove the two screws securing the brush-holder, withdraw the brush-holder and the commutator. Clean the commutator with a suitable electrical cleaning spray. Using a multimeter switched to resistance check the resistance of each adjacent segment of the commutator. If there is any substantial variation in any of the measurements the tacho needs replacing. 
e) Re-assemble the motor, power-up the machine, check and adjust the axis lag, (lag should be 1mm at a feedrate of 1000mm/min.). Check and adjust axis reference position if the motor or the resolver have been removed. Remember to datum all axes before running on programme. If the axis is still faulty, continue with paragraph (f).
f) Disconnect the two wires to the axis motor at the ALC contactor (numbered 281 for X, 286-Y and 291-Z) and the D terminal on the drive unit (D1-X, D2-Y, D3-Z). With a multimeter or 'Megger' check the resistance from one of the motor wires to Earth. The reading should be in Mega-ohms for a good motor. If the reading is low (10K ohms or less) it indicates a build-up of carbon around the brush-gear, damaged brush-holders, a faulty commutator or windings. The same check can be made with the motor brushes removed. If the reading is then considerably higher than with the brushes fitted (Mega-ohms), then the commutator or windings are faulty and the motor needs repair or replacement.