G540 z touch plate stopped working

I have my cnc machine running on a g540. Connected to input 4 is my touch plate which connects with a single wire to an aluminum block.

I have had no issues with the setup until today, all of a sudden Mach 3 will not sense the touching of the router bit to the block.

I have checked the wire and it is fine, If I measure the voltage between the block and the router bit, it measures 11.5v. All other input pins work properly with the proximity sensors.

I have changed out the g540 with a spare unit and that did not seem to change anything either.

I am looking for some input on this situation? Could I have accidentally hit something in Mach3?

Thank you for any help.

BenG
Kansas City

11.5V between the block and the router bit looks correct

As you have substituted the G540 with a spare

I would check / replace the printer cable connecting the G540 to the PC printer port / motion controller
( are you using a PC printer port or motion controller ? )

If that makes no difference
check the mach3 setup has not been corrupted – start with pins and ports -
some times mach 3 needs re-installing

John

It was late last night when I posted, so here is a response to John along with a little bit more information:

I do have a motion controller between the pc and the g540. It is a uc300eth-5lpt. The parallel port between the motion controller and the g540 was originally connected to the port 2, as a diagnostic, I move it to port 3, this did not change anything. (I do not have a spare uc300).

I changed the mach3 config file to an older config file, and that did not work either.

I have a licensed copy of uccnc installed on my machine and using that did not change anything.

One thing I am going to try this morning is to move the touch plate wire over to input 1 and see if that might work.

Also, I do not have a spare parallel port pigtail on hand, so I will pick up one and see if that might have developed an issue.

I tried moving the touch plate wire to input 1 and this did not change anything.

its possible you have a high resistance connection that limits the current through the touch probe but not that high to affect the open circuit voltage you measured


a while ago I produced this partial G540 diagram based on an early version of the G540 with 4 outputs found on this site

Attachment 426822

after looking at the ILQ74 data sheet and seeing the volt drop across the LED is about 1.3V

the short circuit current when a G540 input is connected to ground
as happens when the tool touches the touch plate should be 4.8mA ( 12v - 1.3 v / 2200ohms )
you can check this by connecting the G540 input to ground via your multimeter ( set to the 200mA range )

to check the isolated output of one of the four G540 input circuits (input 4 in this case )

set your multimeter to the 200 ohms range and connect it
between the 25 way D-type ground pin 18-25 and pin 13 ( for the other 3 inputs test between ground and pins 10 to 12 )

( with a digital meter connect the black negative probe to the 25 way D-type ground pin 18 to 25
and the red positive probe to pin 13

with an analogue meter you need to reverse the leads and
connect the red probe to ground and the black probe to pin 13 )

when the touch probe is closed
the ILQ74 opto isolators NPN photo transistor should be switched on and you should see the resistance drop - maybe to about 20 to 30 ohms

John


PS


DIY BOB tester to indicate the status of inputs 1 to 4 and the E-stop / alarm on pin 15
Attachment 426834


an alternative version for use with the G540 could be increase the resistors to 2200 ohms and use a 9V radio battery with the negative battery terminal connected to a ground pin18 to 25

Attachment 426836

NOTE- the 25way D-type connector shown was originally for a BOB with a 25 pin plug
for a Geckodrive G540 with a 25 way socket you need to use a 25 pin plug on the tester (or use a gender changer)


PPS
original G540 PDF schematic


Attachment 426842


PPPS

simple logic probe / diode connection diagram

Attachment 426840

John, Thanks for your input.

After further reading I decided to move the ground wire to the ground plane used for the g540. Originally I had a single wire from the g540 input 4 to the z probe plate and using the routers ground to close the circuit. Now, I have two wires, one from the ground plane and the other frome the g540 to the probe. And now an alligator clip to connect to the router bit.

Working perfectly again.

Thanks!

a good result !

glad to see its working again

John