Siemens SIMATIC S5 Manual page 281

Planning
Select the mode "JOG 1" and press the "forward" or "reverse" key. The drive must now
move at a uniform speed.
(If the drive is running at a uniform speed, you can continue and check the limit switches.)
Problem
Motor "howls", but does not move
Motor jerks and stops
Motor accelerates and then stops and "howls"
Error message:
Axis waiting for external start
If the axis switches to the "running" status and if the actual value is being incremented or
decremented, but the drive is not moving, check whether pulses are being output at the TN or
TN-N output. Measure the pulse frequency and pulse width with an oscillograph.
The signals are correct at the output of the
IP247, but the motor is not moving.
No signals can be measured at the output,
although an actual value is being counted.
Check the function of the limit switches which send signals directly to the power unit.
Check whether the travel direction is the direction you require in the "JOG"
mode.
If the direction is not as required, change the setting of the power unit
direction level or change over the RP and RP-N connections in connector ok
X4-X6.
7 - 1 4
Possible cause of problem
Start/stop frequency too high
Rate of frequency increase too high
fmax too high or load torque too high
The signal at the statistop input is high
The signal lines to the power unit have been
incorrectly connected,
The reset signal is permanently active.
You may have to change over RS and RS-N
The power unit may require a separate enable
signal.
The transmitter power is not correctly
connected or there is a hardware fault on the
module.
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