Meldas 520 AMR, RS 232 Signal ground wire gets hot

[CNC Viking]

Hi all Meldas friends!

I recently bought another Feeler FV-800A with 4:th axis and Meldas 520AMR control. The annoying thing is that the RS 232 does not seem to work on this one. The setup and configuration is an exact copy-over from my other Feeler. I even use the same PC, same serial cable and the parameters are set exactly as on the other working Feeler. But on this one I get no data transmission and a hot signal ground wire. I believe it indicates a ground potential which is odd, as I power the PC exactly as I do with the other machine.

Can it be something inside the control's communication card QX522?
How do I check that the RS232 port on that card works?

Meldas 520 AMR control.



My RS232 cable set up for hardware handshake.

[Caprirs]

Certainly could be a grounding issue. Specifically, it sounds like something on the CNC is not properly grounded and is connecting to ground through the PC.

If you have a multimeter, leave the RS-232 cable connected at only one end (either PC or CNC) and leave the other end disconnected. At the disconnected end, check for any voltage between the metal housing of the serial connector and the PC/CNC. Ideally, there should be no voltage. Check for both DC and AC voltage. I have seen machines in the field with as much as 30VAC between the machine and the PC.

[CNC Viking]

Thanks Caprirs,

I take it that you mean measuring voltage between the D-sub connectors metal frame and the PC's or CNC's frame ground?

I will check the "new" CNC first as it is when my PC + cable gets there the trouble begins.

[Caprirs]

Yes, the metal frame/hood/shell. Hopefully, there is some voltage there so some simple grounding will solve the problem. Much cheaper than sending the board into Mitsubishi!

[CNC Viking]

I sure hope it's not the board.

One interesting thing, I found out yesterday, talking to the previous owner:

When he connected his laptop, trying to output the parameters etc., he encountered the same problem = the signal ground wire got hot and there was no transmission. But as soon as he removed the laptop's charger that was attached to an AC line, it worked.

[A1CNC]

I have a couple older Leadwells with Meldas MO controls, I have had trouble communicating with one using a laptop while the other Identical machine using the same cable, same laptop works fine. The only difference was where I plugged the laptop into the wall. I have been meaning to install a transformer in the machine to power the laptop from. This way, the laptop ground and the machine ground will be connected and hopefully get rid of any ground issues.

On another note, I am interested in adding a 4th to My machine with the Meldas 520, Could you tell me how the 4th is set-up on yours? Is it a 4th drive in the control or a stand-alone like a Haas etc..? Is it an indexer or a simultaneous 4th?

[CNC Viking]

A1CNC,

So the laptop worked with both machines when not plugged into the wall? Then, when you plugged it into the wall, one of the machines got hot wire due to ground issue? Which wire got hot and did it transmit or not?

I tried to power my PC from the cabinet's 220V line (after the large main transformer) and the ground from the ground plate inside the cabinet.
Same result, hot signal ground wire and no transmission.

I suspect that there is something wrong inside the QX 522 CRTC Board.
What exactly is "signal ground"? Plain Frame Ground -or what?
How can I check my RS232 port? Check that it transmits and receives signal etc.

[CNC Viking]

A1CNC,

Re. your 4:th axis plans:
Meldas 520 AM is already prepared for a 4:th axis = "B" axis.

You need to get a servo amplifier (drive) MDS-A-SVJ-06 or MDS-B-SVJ2-06 and a 4:th axis rotating table with a Mitsubishi servo motor (HA40NC-S complete with encoder) on it. I think you can use the larger MDS-A-SVJ-10 or MDS-B-SVJ2-10 drives as well, but I am not sure (it has to be checked).

You also need a signal bus cable between the drives, + encoder cable and power cable to the servo motor. Then you enable 4:th axis in the parameters and load all parameters for the drive.

The servo drive for 4:th axis is the one to the far right. As you can see, it is smaller than the others.



The 4:th axis should have one of these. The larger X-, Y- and Z-type ones do normally not fit on a rotating table.

[A1CNC]

Thanks for the info on the 4th.

As far as communicating,
I could send/ receive at slower speeds,(2400 baud) which is pretty useless to either machine and (1) machine I could reliably drip-feed. I never noticed a hot wire at all but I never checked either.

When I 1st tried the same settings on the 520 I couldn't communicate, I finaly found settings that work but they are different than my other machines with the Meldas MO controls. I will compare my cable tomorrow to yours, and get the settings that work for mine.

Do you have the manuals for your 520?

[CNC Viking]

Follow this thread to get Mitsubishi Manuals:

http://www.cnczone.com/forums/mazak_...ml#post1054135

[CNC Viking]

As the setup of the new machine is more or less similar to my other working Feeler, I bit the bullet and bought an RS 232 Optical Isolator:
http://www.exsys.ch/download/catalog/ex_47925.pdf
I will install it durning the nearest days an report the outcome.


On my earlier Feeler I also installed a 2 port Quatech SDS (Serial Device Server) that sits in the machine cabinet. It is fed by an Ethernet cable and delivers RS232 signals to the CNC. I bought the DSE-100D model.
http://www.quatech.com/pdf/sds.pdf
It works well, but sometimes the transmission stops during machining and I do not know why? My question is: Can this server eliminate my ground loop issues with the new Feeler, since it is an Ethernet/serial adaptor? Or will the problems continue since it is not galvanically isolated?

[Caprirs]

The Exsys device will provide isolation from grounding issues. The Quatech device does not appear to have any isolation based on the description.

On my mills, I use units from Betatronics to prevent ground loop issues and ensure more reliable transmission.