Defiance DMC 2001 Need Help to figure out a problem

[Anatoliy_w8]

Just got that magic machine from auction. After start up and home axis got FAULT:AIR PRESSURE. I got schematic and controller manuals but there only 1 pressure sensor in machine and fully functional cause I see INPUTS from menu and it changed if disconect a pressure, even if short a sensor(switch) port belong to change value. Now I got no idea where problem should be. May be some one familiar with that type of machines?

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[he1957]

The pressure sensor may register open and closed circuit but the internal membranes used to detect the value needed for the controls to register correct pressure may be bad. Replace the sensor if all other air flows check out ok.

[Anatoliy_w8]

Unfortunatlly it is a pressure switch connected to input, it doesn't have analog ouput and can't measure actual pressure. On a sensor litte dial to set threshold. May be there some other sensor and I have wrong diagrams but cant find any. There only weird think air supply to linear scales... may be inside some measure sensors

[bbgun]

Have you tried calling Creative Evolution (dba Geonics)? They still support the old Defiance machining centers.

[fdarling]

I have a Defiance DMC from year 2000 that I bought used. It is fully working, so if you need any cross-referencing of it's behavior or correct sensor input states let me know.

The air pressure sensor ultimately hooks to the pin TB2-6 on the Delta Tau ACC-34AA opto-isolator board. I attached a photo showing the board with the relevant wire circled in violet.

Here is what I would do:

1) purposely remove air pressure and reintroduce it while checking the status LED for that input. If it does not change, then either the sensor is bad, or that input is fried.
2) disconnect that wire from the board and measure it's voltage with respect to signal ground. If it has a constant 24V with respect to signal ground despite changing the air situation, then the sensor is definitely bad. If it has a constant 0V with respect to signal ground, then it's possible you must check to see if it's normally floating/pulled up by the opto-isolator board, in other words switching from disconnected to connected to 0V, which brings us to the next step...
3) If it's always at 0V, then it's safe to attempt measuring resistance to signal ground. If the resistance doesn't change either, then you've fully tested it and the sensor is definitely not changing it's characteristics despite the air situation changing.
4) adjust or replace the air pressure sensor!

Also note that on my machine there is a cutoff near the air inlet that can be twisted to say either "exhaust" or "supply". It must be on "supply" to allow air into the machine!

I hope this information is useful, despite my reply being 9 months after the original post...