Odds are that you have a stepping motor BOSS machine. It is typical of these to stall and whine as if they are trying to move. You must understand what a stall is. The control accelerates the motor to a certain velocity. If the motor cannot keep up it will move bacward to the closest/strongest electromagnet (field). It then occilates between poles, hence the whine, and it does not move. The causes are insufficient voltage or current or drag on the motor or a weak motor. Some of these machines used screw in fuses which developed a resistance and would overheat. If you have screw in fuse holders (the original BPT were tan in color) replace them. The current at static (drives on and stationary) should be 8 to 8.2 amps DC adjusted at the ACC board. Always turn the drives off before pulling a fuse or hooking up a meter or removing a meter otherwise you mave blow one of the final drive transistors. At staic state from each of the DC drive fuses to ground, I would usually see about 8.5 to 9.5 volts. The most important reading is at the large transformer in the back. IE: wires 11 to 12 power the X axis. This should never exceed 64VAC or you will blow the final drive transistors like candy (2N6547). If other transistors are used I know immediately as the balance of voltage to current is off. Some times I have to clean the quill with kero to get rid of gumminess. Sometimes the graduated knob/dial at the end of the motor shaft rubs the cover and this can cause drag. When the motor turns at rapid the DC volts goes up to about 60VDC and the current drops to about 2.3 amps. As the magnets decay from heat and age, this current goes up which means that the same torque is not there and the axis can stall. This is also why when you turn the motor by hand you feel the poles as a growl. This is not a bad motor. But as the motor ages this growl diminishes. The RCK or ZCK board can be adjusted for a lower rapid rate and this can buy some time. I hope this helps.
George.  |