Tweco Troubleshooting Power Supply - Manual (Page 39)

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Sensor disconnected – flow sensor comes with wire about 1 ft. long and a
connector that connects to a 3 wire harness. This could be disconnected or CN13
where the harness connects to PCB5 could be disconnected.
Defective Flow Sensor – If sensor is not putting out pulses it may be setting at
either +5V or 0 V. Measure for +5V on CN13-1 (common is TP0 on PCB5 or
TP1 on CCM) to confirm that the +5V supply is present. Then measure CN13-2.
The output of the sensor is a series of pulses which are best measured with an
oscilloscope however a voltmeter can be used as it will read an average
somewhere between the pulse peak and zero.
The no load output of the flow sensor is a series of rectangular pulses with
amplitude 0-5VDC. The output impedance is about 5K.
0-5V
5K
10K
CN13-2
On PCB5 it goes into a transistor with 10K base resistor so for the signal at
CN13-2 the 5V peak is loaded down to about 3V relative to TP0. If the flow
sensor is disconnected CN13-2 is zero V as there is no pull-up resistor.
Expect the normal signal at CN13-2 to be around 1-2V. The flow sensor
consists of an IR LED and photo transistor with a blade that breaks the light path
between the LED and photo transistor as it spins. If there is no flow one would
either measure zero V or 3V depending on if the blade is blocking or passing light
when it is stopped
.
If measurement is either zero or +3V (or higher) the sensor is likely to be
defective.
PCB5 – If previous measurements do not indicate bad flow sensor, measure at on
pin 6 of the 34 ckt. ribbon cable, CN11 to J36. The output of PCB5 on the ribbon
cable is open collector with 4.7K pull-up in the CCM. Here the pulse is between
0-5V with normal flow being around 2-4V. Either zero or 5 V indicates PCB5 is
likely defective.
CCM – If previous measurements do not indicate sensor or PCB5 is bad then fault
in probably in the CCM. Other possibility, the 34 ckt ribbon cable could be open
or shorted.
4-5
Low Coolant Level Warning
If coolant level becomes low during a cut it does not shut off the system but
does flash code 4-5 as a warning. See sect. 4-1 for troubleshooting low coolant
codes.
The 5 Group relates to CANBUS communication errors. The GCM 2000 & 2010
also have some codes to consider. These are listed following this Group 6.