Those Nasty Occasional Problems!

Rybett Controls WebDoc 105   (Copyright 2008)   Return to [Index]

Installations that work most of the time but occasionally have a problem are very difficult to troubleshoot. Don't overlook loose wiring crimps and contact problems. Then, consider our list of possible causes:


Electrical noise from welders, discharge machining and plasma arc burners can play havoc with DNC communications. If you suspect such interference, try experimenting with various machines running or not running. When you discover the noise source, route all DNC cables as far away from the noise as possible. Also, do not route DNC cables along with power wiring since noise can easily travel these lines. In the case of a Camstore LPT BTR, move the PC computer close to the machine, use as short a cable as possible and tie a ground strap between the PC chassis and the machine cabinet.

In severe cases, you can unplug DNC cables when not in use. Or, you can place RS422 or fiber optic converters at each end of the affected DNC cable. Rybett RS422 and Fiber Optic Kits are available.


If problems tend to occur on very hot days or in the late afternoon, perhaps something is overheating or just temperature sensitive. You can try directing a fan on suspicious components as an experiment. Once a temperature problem is localized, the module can be serviced.

If your PC computer mysteriously reboots, the problem is probably related to power. Move to a different AC power plug. If the problem persists, change the power supply in your PC. If your PC has been recently upgraded to a faster motherboard, the old power supply may be generating transients that were ignored by the slower motherboard.


Sometimes an occasional problem seems to occur only while the machine is executing blocks with certain related instructions. Such symptoms generally direct attention to the NC controller since DNC software and BTR hardware simply send data without trying to act on data. Only the NC really understands what's going on. There is one interesting exception, however. On older machines, spike suppression diodes and RC components on solenoids, coils and motors can degrade. This can cause local electrical noise when these actuators are energized and de-energized. Such events may occur in response to specific program data such as M and T codes. If this description fits your situation, take a close look at your coil suppression circuits.