Weird problem with Fanuc RS232 blowing fuses

New Doosan Lynx lathe with Doosan Fanuc i control. Replaced 25 year old Lynx , using the same RS232 cable and power surge protector. When we plug in the RS232 connector and surge protector the connector gets HOT and within a few minutes blows a fuse in the control. Not communicating through the port, just connected. Move the cable and surge protector to my Puma machine with a 21iTB control right next to it, works fine, communicates fine, no heat. Move it back to the Lynx, I can actually communicate if Ido it quickly before the fuse blows, but it gets HOT (too hot to touch). Ellison has changed internal cable, and connector, no help. Fanuc changed board the RS232 is connected to, no help. I've had Fanuc controls for 30+ years and never had anything like this. Fanuc seems baffled as well. I can use a memory card for now, but we have a DNC system that I prefer, so have to figure it out. It's under warranty so, it will get fixed, but any on have a clue? We have tried 2 other new surge protectors, same results.

What fuse blows? I’ve seen similar on a brother where the 24VDC was touching a ground and had the machine floating on some strange voltages. In that case an improperly trimmed pin on a PCB was left long and touching sheetmetal.

It's a fuse on the board that the RS232 connects to. There is a cable from connector on the side of the control that we plug into, that goes to a PCB in the control, it's a fuse on that board. Machine functions fine otherwise, we are running parts, just can't have anything plugged into RS232 port.

Disconnect the wire on pin 7 on the rs-232 connector on your cable and see what happens when it’s plugged in.

New machine? Why not just use the USB port next to the screen?

Fanuc controls feed +24v on pin number 25 on most machines.
This is for portable DNC boxes. ( FANUC Handy-File and the like )
That is what the micro-fuse in the back of the LCD is protecting.
This is not the multi-amp fuse feeding the entire LCD.

Check pin 25 against the Frame Ground ( Connecter Shell ) and also against pin 7 on the DB-25.
A floating ground is the most likely issue on the machine.

Most machines will RS-232 just fine with the micro-fuse blown.

The PC based controls, 180i, 310i are different.

RJT said:

It's a fuse on the board that the RS232 connects to. There is a cable from connector on the side of the control that we plug into, that goes to a PCB in the control, it's a fuse on that board.

Click to expand...

Vancbiker said:

Disconnect the wire on pin 7 on the rs-232 connector on your cable and see what happens when it’s plugged in.

Click to expand...

It will be Monday before I can try this.

That didn't help, blew another fuse.

Disconnect pin 25 on your cable.

Vancbiker said:

Disconnect pin 25 on your cable.

Click to expand...

Should I re install pin 7?

Yes

Also, is the machine grounded with a separate ground wire and that ground tested for continuity to something like building ground or a metal water pipe? Who wired in the new machine?

Ellison installed the new machine, it is using the same wiring as the Lynx machine it replaced (and using the same rs202 cable). Initially 25 years ago when the first Lynx was installed, our electrician would have done the wiring. Same electric company that did the initial wiring in the building and has wired the other 15 CNC machines in our building. I'm sure the machine is grounded, but not with a separate grounding rod that goes through the floor (we have done that with our EDM machines, but not with any CNC mills or lathes). I am out of fuses, so will have to wait until I get more to try this out.