Denford Software & Machines

Hi I hope you can help me please. We use an old Orac cnc lathe for our
engineering careers stand and it has developed a fault. I have had our
companies electronics engineers look at it and as its a intermittant fault
it is difficult to get their time away from upkeeping all the shop floor
machines to try and fault find it.
The fault is that the machine will not fully switch on, on switching the
mains switch the fan and m/c light come on but nothing else such as the
keyboard or screen. If I keep switching on after about 10 - 20 times it
eventually powers up and is perfect all day. The main relay and contactors
are clean and OK as checked initially by our engineers, is this something
youve heard of in the past.
Orac CNC AC22067B July 1987 !
Control 78074358
I hope you can help as it does interest the students enough to look at an
engineering careers stand!

I have never really seen an orac, but a few basic things spring to mind..

Check the obvious things like:

• Relay contact quality (sounds like you already have).
  Fuses are making good contact, and the fuse wire is physically sound.
  Voltage levels around the board are good and what they are supposed to be
  Its possible the PCB has a dry joint, or broken track that fixes itself once it has warmed up

If the fans is coming on then the 240V in is good. It sounds a bit like a power supply problem to the 'processing' section if neither the keyboard or screen work. On the X axis, try removing the cover on the back of the 'table' - green sheet metal with 2 screws. When you remove this you will be able to see the puleys for the axis drive.

With the power turned off, try and turn the pulley. You should be able to rotate it. Now turn the power on. Can you still turn the pulley (make sure the Estop is out) - if the motors are powered up you shouldn't be able to turn them easily.

I can't remember without looking at the circuit diagrams but I would expect the logic and drives to be on different supplies so if you can still turn the motors with the power on then I would think the problem is most likely going to be between the mains in and the transformers.