earthing/grounding help please

[scoot]

hi guys.

when my projector is turned on but not connected to my computer i get lots of noise on the galvos. its fine when it is connected.
my projector case is connected to mains earth.
scanner amps are screwed to the case,scanner psu is screwed to the case.
my fb3 card is running from a 5v switching wall wart made by fuji film but this has no earth?
also do the laser heads need to be insulated or connected to the projector case?
thanks.
scoot.

[steve-o]

Some heads are isolated, some are not. check the potential difference between the ground of the PC cable and earth gnd.

[stanwax]

It may be worth putting some grounding in to the scanner inputs so they dont float and pick up noise with no input present. If the amp input is very sensitive then this can occur. Pop a 10k resistor from the input to ground & this should do the trick but also do as Stave suggested and check what potential there is between the parts when powered up but they are not bolted together.

Rob

[Jem]

Hi Scoot

I had the same problem, a couple of resistors did the trick nicely.

I'm no electronics expert, but if you contact 'Wiring Monkey' on this forum (sent him a PM), he'll tell you exactly what he did to sort my problem out.

Cheers

Jem