Spindle Speed Potentiometer Feed Pot fault and Repair
EEC Ltd were contacted by a local manufacturing company experiencing a spindle-speed issue on their Dugard 1500 CNC machine, fitted with a HEIDENHAIN control.
During both program run and manual spindle speed input, the spindle speed would oscillate between 50-100 rpm without the operator touching the machine control panel. No error messages were logged or identified by the HEIDENHAIN control.
Diagnosis of the Spindle Speed Fault
With Depth of knowledge and previous experience at hand, EEC engineers immediately diagnosed the spindle-speed potentiometer feed-pot to be at fault by using test equipment that only HEIDENHAIN Service Partners have access to. Being an appointed HEIDENHAIN service partner, EEC were able to quickly and accurately monitor the signals, voltages, inputs and outputs that the control was sending and receiving. By monitoring these signals we observed that the voltages that the control was sending and receiving were correct, and that the outputs were also correct. However the input of the spindle speed potentiometer was oscillating whilst not in use, which confirmed EECs initial diagnosis of the spindle speed feed potentiometer.
EEC advised that the potentiometer was at fault, and the customer elected to follow EEC’s advice and replace replace both the spindle speed and travel feed rate potentiometers at the same time. Since both potentiometers were of the same age and one had failed, AND the keyboard needs to be removed to fit the new potentiometers – it made logical sense to replace both components.
Potentiometer Repairs
To keep the customer up and running with the machine and ensure stable spindle speeds, EEC engineers removed the keyboard and swapped the travel speed potentiometer and the spindle speed potentiometer in the ports on the back of the keyboard. This method also serves as a secondary means by which to identify the spindle-speed potentiometer was at fault – as the spindle speed was now stable.
EEC placed an order for the parts that morning with HEIDENHAIN Germany, with a typical delivery schedule of 2-5 days to arrive. HEIDENHAIN Germany operate rapid response shipping capabilities, with the replacement potentiometers delivered to EEC the following day.
EEC visited the customer to replace the 2 potentiometers, culminating in a 2-day turn around from the customer contacting EEC to report the fault, to the customer’s machine back up and running with completed repairs.
The control showing zero errors whilst still oscillating spindle speeds.
Showing the potentiometers swapped ports in the back of the keyboard.
A reminder for the customer that the feed potentiometers have swapped.
Identification of the main keyboard and location of the potentiometers.
Replacement potentiometers fitted and aligned for 0% and 100% to be accurate to the print on the keyboard.
Showing the now stable spindle load and speed once the potentiometers had been replaced.
