Check the voltage on the Z-Electronics Module (ZEM) circuit board (see Figure 272).
The voltage must be +6.0 to –6.75 volts symmetric to within ±0.2 volts when the Z-servo
loop is broken (the Z-stage is resting at its bottom hardstop). If the voltage is +6.0 to -6.75
volts symmetric to within ±0.2 volts, do not perform this procedure. Also, check the ESI
System Log manual for an indication of other problems