Service manual

Electrical Service Manual V4.0

1-4

CENTRAL COMMAND I

GENERAL DIAGNOSIS OF THE CURTIS SYSTEM

The Curtis system diagnosis is performed in many cases by the substitution of known good

parts into the system. This system of diagnosis, although seemingly crude, is very effective

from a time management stand point.

Some Curtis systems uses a “ﬂash code” system to assist in diagnosing it. There is either

an LED on the controller itself or an LED located on or around the control panel of the ma-

chine.

There is a list of parts needed to diagnose the system using the parts replacement method.

(See Appendix A)

The following is a basic check list to follow in the event of problems

1. Check Battery Voltage.

2. Check battery cables for physical damage and test with a hydrometer.

3. Load Test the batteries.

4. Do a voltage drop test on the battery cables.

5. Check the cable to the traction motor and see if it is tight

6. Is the Curtis control “On” ?

7. Are the relays OK?

8. Is the potentiometer OK?

For further diagnosis see the chapter for the controller your machine is equipped with.

POTENTIOMETERS

The potentiometer on the Curtis system use a high and a low reference voltage supplied to

the outside terminals of the potentiometer. These voltages are combined by the potenti-

ometer to give a smooth sweeping voltage of from 0 to 5 volts DC. This sweeping voltage

signal is then sent to the controller which in turn propels the machine at a speed relative to

the potentiometers position.

TESTING THE POTENTIOMETER.

With the machine power on using a quality digital voltmeter, measure from one outside ter-

minal of the potentiometer to the other outside terminal of the pot. You should see from 4.7

to 5.2 volts across these terminals with the key in the “on” position. If you have between

4.7 & 5.2 volts here then touch your negative meter probe to the negative battery terminal

or negative buss bar and measure at the center terminal of the throttle pot with your posi-

tive lead and slowly rotate the pot. You should get a smooth sweeping voltage from 0 to

0.2 volts at one end of travel to 4.8 to 5.2 volts at the other. The voltage should rise or fall

smoothly through the travel. If the voltage is jerky along the way, the pot is damaged and

must be replaced. If you did not have the 4.7 - 5.2 volts across the two outside terminals

see the appropriate diagnostic section for your controller.