On 12/26/2015 07:16 AM, John Thornton wrote: > I just checked the ground to housing on the VFD filter, VFD, computer, > and the smaller filter and they are all internally connected to ground. > The VFD is controlled via modbus so I don't know how to check that cable > (which is just a phone cable with a phone jack on one end and a DB9 on
Phone cable? Can you try to replace it with Cat-5 or a better twisted pairs cable? > the other end to connect to the computers serial port, it's a Automation > Direct cable not home made. There is one other thing you might want to try, install ferrite core on power or other cables. It takes a lot of RF noise out. Search for "Ferrite Core Cord Noise Suppressor" > > Is injection to the mains coming back to the machine somehow? > > JT > I opened older power supply for 1U computer to remove the dust recently. I'm glad I did. Just looking at it, I could tell that there were 3 bad 3300uF capacitors. Their tops were not flat. PSU still worked with small motherboard and one disk drive but the power was not clean for sure. It is possible that you have a similar problem, i.e. old electrolytic caps in your VFD or power supply. Very critical in analog circuits. Electrolytic caps are the most unstable electronic components and need to be replaced in old equipment. Some large caps can be refurbished but that's an extreme situation in very old computer restoration efforts. Merry Christmas, -- Rafael ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
