LS SERIES SERVICE MANUAL
ISSUE 4.0 CROSSHEAD DRIVE 3
The overcurrent action is similar when the machine is driving downwards except that the motor
current will develop a voltage across R10 and this voltage is sensed by the comparator IC4B
and set the latch IC3B. The Q output of the latch will go High and light the Compression
Overcurrent LED (DS4) to indicate that the motor circuit has tripped.
If the Tension Overcurrent LED (DS2) or the Compression Overcurrent LED (DS4) lights, one of
the inputs to IC5A (pins 1 or 2) will be pulled Low and this will pull IC5B pin 6 Low to generate a
FAULT condition.
When a fault condition occurs, the DISABLE signal from IC5B pin 4 will go High and will switch
off the PWM Driver IC, switch off the Drive LED (DS3) and switch off Q3 to give a FAULT signal
to the microprocessor. When a fault condition occurs, a "Motor Fault" error message will be
displayed on the console.
Note that the machine can also show another error condition called "Drive System Error". This
error message shows that the crosshead is not in the expected position, i.e. the microprocessor
has calculated that the crosshead should be at 25mm but the crosshead is actually at 20mm.
This can be caused by a faulty encoder, low mains voltage etc. so may not be caused by a
faulty Motor Drive PCB.
7.4 Power Dump Circuit
If the power is removed from drive motor when it is running, it may act as a generator and cause
the power supply voltage to increase. The comparator IC6 monitors the high current power
supply and if the voltage exceeds approx. +80V, the MOSFET TR2 will be switched on and the
excess power will be dissipated in the "Power Dump" resistor R32. The power dump action is
indicated by the POWER DUMP LED (DS5), which will briefly light when the motor supply
voltage goes too high.
7.5 Safe Line Circuit
The safeline circuit isolates the Motor Drive transformer from the Motor Drive Power Supply until
the operator has pressed the safeline button. This ensures that if the Motor Drive PCB fails,
then the motor will not run when the machine is first switched on.
The safeline circuit contains a relay (K1), which has 2 sets of change-over (C/O) contacts. The
first set of contacts (4, 5 and 6) are used to power the safeline lamp and also provide a "Hold-
on" supply for the relay. The second set of contacts (1, 2 and 3) are used to connect the
transformer to the bridge rectifier on the Motor Drive PCB.
The safeline lamp is connected to P4 pins 1 and 2. Pin 1 is connected to 0V and pin 2 is
connected to terminal 5 (N/C-1) of the relay K1. When the machine is first switched on, the
safeline relay is de-energised so the +12V supply fed to K1 terminal 4 (common-1) is connected
to terminal 5 by the N/C contact. This +12V is fed to P4 pin 2 so the yellow safeline lamp is lit.
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