I have a K40 with optical home position sensors, I have had intermittent issues with them and have just replaced both sensors. The X sensor switches it’s output from around 0.4 volts to 3.2 volts and seems to work ok, the Y sensor only switches to 1.6 volts, this does not seem to be detected by the Cohesion 3D board and results in the gantry crashing into the back of the machine. (I have replaced the Cohesion board with a grbl board and get the same result) all the cables seem to be ok.
Any suggestions??
In standard Transistor-Transistor Logic (TTL), a logic “0” is typically represented by voltages between 0V and 0.8V, while a logic “1” is represented by voltages between 2V and 5V.
Your 1.6v does not qualify as a Logic “1”. Replace the bad Yaxis sensor.
As I said in the original question, I have replaced the sensors, that’s why it’s puzzling to me
One thing I know from years of experience repairing automobiles, just because the part is new, does not mean it’s good. You may have a faulty sensor or it may not be being provided with the correct voltage to operate properly.’
Just for testing, swap the connectors atthe control board and see if the problem follows the sensor or if it stays with the connection.
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@thelmuth was just about to say that !
Check if the Y switch supply voltage is actually 5V, and as Tim said - switch the sensors at the plugs to see if the problem moves (can trigger y manually when x home movement starts).
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A design putting optical sensors in a machine generating copious smoke seems … suboptimal.
After you get the (new?) sensors working, they’ll require cleaning on a regular basis. Whenever it has trouble homing in the future, run a swab (maybe damp with alcohol) through the sensor gap to remove crud from the optical surfaces in there.
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Also, as an addendum to my last comment you don’t really to run the home cycle to check the sensor functionality (to avoid that brief moment of panic when the switch doesn’t work and it’s about to crash!) because if it’s a GRBL board it should report sensor status as @misken explains so nicely here:
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Ok, Im baffled!
I took the sensors out for about the thousandth time couldn’t see any problems, put them back and now it’s working! I haven’t changed anything as far as I can see, same sensors, same cables but now it works. I think it’s haunted! it’s either the pixel pixies or the laser demons, maybe I should get a priest involved!
Sounds like there was a poor connection somewhere and removing / reconnecting made it better.
You are probably correct, but I really have lost count of how many times I have connected and reconnected it.. now it’s working I’m afraid to touch it!
Be afraid, be very afraid! 