VF3SS Alarm 626 proximity switch malfunction

[GiroDyno]

We just commissioned a new to us 2007(maybe 08?) VF3SS. Haas techs were in yesterday adding probing and breaking in a new spindle. We mounted our fixturing this morning and were hoping to take some test cuts but out of the blue the side mount ATC stopped working with an Alarm 626; the pocket swings down, but then the tool change halts and throws the alarm.
We can manually trigger the solenoid and the pocket swings up and down fine so its not the valve, or the actuator. We then checked the diagnostics page and the Pocket Down bit is always reading 0 while the Up bit switches when the pocket is moved, so the "Down" sensor must not be functioning. We took a few panels off but cannot figure out how to access that switch without removing a lot of hardware. The Haas video I found is definitely not the same ATC we have because the sensors look readily accessible.
I am hoping somebody out there has a secret shortcut to accessing the sensor that reads the actuator position!

 

[GiroDyno]

The ATC worked this morning, so we were getting ready to set up again and it stopped working again...
I followed the instructions in this video from Haas:
I was able to access the proximity switches and test them with a screwdriver verified they and functioning (2:35 in video)
I checked them with a multimeter (3:50 in video)
I tried to jumper the pins on the I/O board (6:00 in the video)
Everything appears to be working from the sensor back to the board, seems like an issue in the controller itself? Any ideas on how to troubleshoot this? If we call our dealer they will just set up a service appointment for two weeks from now, I'd rather try and figure it out myself today.

 

[wlbraker]

GiroDyno,

We are having the exact same issue with a VF8. Did you ever figure this one out? Curious to learn what you did to fix it.

Thanks,

 

[GiroDyno]

I don't remember which machine this post was about, we have several VF3s all with their fair share of ATC woes. I believe in this case I replaced one of the proximity switches.
Getting to that switch was tedious; involved removing several pieces of sheet metal and getting a lot of cast iron dust and leaky way oil all over me.
When you go to install the new sensor go up from the bottom of the ATC arm, tape the plug end of the new one to the old sensor and pull the old sensor out of the top. This will route your new sensor cable for you which saves you about 20% of the total headache.

 

[wlbraker]

Gotcha, we already replaced the pocket down prox. switch. What makes this issue so hard to diagnose is that it is intermittent. When it doesn't work, you can't do a single tool change for a day or so. If it starts working again randomly (as it did this morning), it will work for several days. It makes no sense at all but is frustrating in a production environment when you have due dates to hit, and you cannot rely on the machine. I should have bought a new one but maybe they aren't much better. Thanks again for your response.

 

[GiroDyno]

Gotcha, we already replaced the pocket down prox. switch. What makes this issue so hard to diagnose is that it is intermittent. When it doesn't work, you can't do a single tool change for a day or so. If it starts working again randomly (as it did this morning), it will work for several days. It makes no sense at all but is frustrating in a production environment when you have due dates to hit, and you cannot rely on the machine. I should have bought a new one but maybe they aren't much better. Thanks again for your response.

Yeah, one of ours does this every Tuesday morning, also bought used, it came delivered with a pile of 2x4s loose in the cabinet that I assume were meant to brace the spindle in transit... You get what you pay for (free shipping)
Turn if off and turn it back on usually does the trick.