VFD interference problem

[cropwell]

I can see one problem straight away. You have no main power to the BoB. In the (invisible) picture below the two middle connectors on the right are the main power (12 - 24v) for the BoB electronics. Without that you will get all sorts of random effects.

I tried to copy and paste from the pdf of the BoB manual, but it didnt work - anyway OP has BoB manual.

[eurikain]

I can see one problem straight away. You have no main power to the BoB. In the (invisible) picture below the two middle connectors are the main power (12 - 24v) for the BoB electronics. Without that you will get all sorts of random effects.

I know the pins you are talking about Rob :) Even when the BOB is powered by the 24V PSU, there is still noise :(

[routercnc]

I seem to remember that you can also power it through the USB socket. You could try this from the PC, if this works then longer term use a USB plug and lead but cut the cables, identify the power supply cable and wire it to an external 5V supply.

[eurikain]

I seem to remember that you can also power it through the USB socket. You could try this from the PC, if this works then longer term use a USB plug and lead but cut the cables, identify the power supply cable and wire it to an external 5V supply.

Yes, that's right, but there are two terminals made to replace the USB port, and I'm currently using them:

[JAZZCNC]

Yes, that's right, but there are two terminals made to replace the USB port, and I'm currently using them:

This could be your problem. The BOB is tying PC ground thru the PP cable to GNd on the 5V supply. For test remove the 5V and power bob using USB.

Regards Spare cheap BOB's that's like simple adding 2+2=4.???. . . Crap + Crap = Crap so why bother.!

[eurikain]

This could be your problem. The BOB is tying PC ground thru the PP cable to GNd on the 5V supply. For test remove the 5V and power bob using USB.

Okay this one also is a great idea ! That would explain why the noise does not appear when the PP cable is not connected ! I add this as first entry of my checklist.

Regards Spare cheap BOB's that's like simple adding 2+2=4.???. . . Crap + Crap = Crap so why bother.!

Always knew you were good at math :D

[eurikain]

Well, guys, problem solved ! Guess who was right ??????????
......
.....
...
JAZZZZZZZZZZ !!!!!

The 5V signal to the BOB had two routes to 0V... getting the 5V from the PC solves the problem :) This is why disconnecting the PP cable was causing the noise to go away, since it would suppress one of the two 0V possible routes.

Thanks for your help !

I do have one more tiny issue:
Mach3 controls the RUN/STOP signal and spindle speed fine, but the BOB seems to output an unstable signal for the spindle speed control. When running, the frequency can't stay still and keeps going up and down by 1-2 Hz, causing the spindle to run faster/slower (you can hear a slight increase/decrease in speed).

I can bypass this issue by disabling Mach3 speed control and only do the RUN/STOP, but while I'm at it, let's fix this issue if possible :)

[cropwell]

I seem to remember that you can also power it through the USB socket. You could try this from the PC, if this works then longer term use a USB plug and lead but cut the cables, identify the power supply cable and wire it to an external 5V supply.

On the BoB OP is using the USB socket is connected by tracks on the board to the PC 5v and PC GND, so the USB socket is not needed.
But those shielded cables won't do much good if they are not earthed at one end.