intermittent "arm board not detected"

[spiyda]

Someone has asked me if I know the possible reasons for a problem with their vacuum pump intermittently stopping and then a message coming up with “arm board not detected” when a job is loaded in rvplace. ( I think he is registering on the forum )

Oddly enough last week I had a similar issue..  at the end of a long run of placing ( lonfg for me, about 5-6000 components)
 "arm board not detected" followed by "z axis switch not found", happened several times.. ( I then changed the "Z" axis switch, but haven't run it since)

What are the most likely causes of the "arm not detected" error?

[Mike]

Probably RS232 port issues, as the arm board is read via the serial port.
Try the armtest program - this continually reads from the sensors - run this and systematically wiggle cables. 
If your machine uses serial ports on the DSP carrier card it could be there as well, and maybe also the power supply to the arm PCB

[spiyda]

Thanks Mike,
still not got to the bottom of the fault. 
It seems to settle down after a while, only occasionally popping up its ugly head.
Each time it seems to be the  Z axis end stop when it fails..
but the sensor has been replaced and the connections cleaned ..
because its a terminal fault, requiring rebooting the machine, i can't get it to sit there in a fault state to find the problem..
and I couldn't get it to occur in the armtest ..  so I guess I'll have to live with it.

[Mike]

I wonder if it might be something like noise from worn brushes on the pump motor?

[spiyda]

I wonder if it might be something like noise from worn brushes on the pump motor?

I'll put a scope on some of the connections and see if there is any noise..
the problem seems to be worse after the machine has not been used for a few days..   
maybe capacitors ?  I'll hunt for electrolytics tomorrow.