Intermitten heater fault


  • Banned

    I devolved an intermittent heater fault bug. Everything has been working fine with no changes to any files for a few weeks now. Thermistor ohms are correct at room temp. No short to ground, frame or any other voltage. on startup I'm get a fluctuating 213-387c temp reading on web control. Actual temp 21c. Now after printing fine, I no longer can. I put an oscilloscope on the thermistor and vssa connection and set to event triggering. The voltage is stable smooth low ripple unchanging wave with now rising or falling triggers and ohms/voltage values remain unchanging. however firmware show temp changing. This is a bug. need help. also everytime bltouch probe triggers the temp reading jumps up 50 or so degrees and back to normal. This is repeatable through even with the probe un mounted remote triggered to eliminate the possibility of vibration on mechanically disturbing the thermistor. some sort of firmware probe thermistor path conflict.


  • administrators

    I really don't think it's a firmware issue, but it could perhaps be caused by a faulty ground connection to the bltouch.


  • Banned

    I explained that I connected a scope to the probe. My scope is far more sensitive than the board. Now change in voltage. no sine variation. No triggering point. Temp readings changing when all probe electric values are a constant. This is the most scientific diagnostic approach. It's not the probe of wiring. It's the computing side in error here. This is the same issue that people have hearing voices. No one else hears it. This firmware or the logic chip sees something that's not there. I am now also getting ajax time outs often. Direct ethernet to router, 400 mm of quality cable. no other device connection errors. Also values in config.g changes to something they are not. Too many unexplained weird behavior.


  • administrators

    The ADC doesn't measure absolute voltage, it measures the ratio between the input voltage and VREF which is the 3.3V rail. Also the firmware doesn't measure VSSA. What I think is happening when the Bltouch triggers is that either the 3.3V rail is dropping, probably because the 5V rail is too low in the first place and it drops further when the Bltouch solenoid is activated, or the VSSA line is changing voltage because something is connected to it that shouldn't be.

    Are you using the internal 5V regulator to provide 5V, or something else? Or are you doing these tests using USB power only?


  • Banned

    Ive done scope tests using the internal with on 24 v supplied externally, Than with usb from battery powered 5v laptop. Also with separate 5v switching from to scope itself. I even supplied all power from scope which is the most accurate method. It's something on board side not voltage or ohm or difference in potential related. there in no change to electrical properties during test. I setup test during a period when the issue is not happening. The scope can be set to only check triggering events every 20 ms and records to a file on an sd card. it also checks ohms in a passive manner and I see the dc wave form un changing. When this issue happens nothing shows up on scope in any way. It's arm related or firmware conflict in nature.


  • administrators

    Have you tried:

    1. Replacing both thermistors with fixed resistors, to eliminate issues with the wiring;

    2. Disconnecting the Bltouch from the Z probe connector, in case it is feeding excessive voltage to the Z probe pin and hence upsetting the ADC?


  • Banned

    Ok now what? still do it.


  • Banned

    What ajax issue. Can't control print after a few hours.



  • If the wiring is too long, the thermistor can catch noise.
    Have you tried twisting the wires and/or using shielded cable?

    I had a similar issue and twisting them solved it for me.


  • administrators

    @sjason1377:

    Ok now what? still do it.

    With fixed resistors in place of thermistors (and ni wires leading from the thermistor ports moff to anywhere else) and the bltouch not connected to the Z probe port, what issue do you observe exactly?


  • Banned

    Bl touch affected temp reading for a second at a time during each probe interval. There is also a static temp fluctuation not related to the probe.
    heat readings from web interface fluctuating between 200 and 300c while hotend is at 20c heater fault indicated as well. nothing file wise has changed. It doesn't do it all the time. it's not noise that's why an oscilloscope was used to check for that. it's clean. The ajax says timed out. print continues, but If I need pause or speed adjustment I don't have control. Also can't reconnect. I have to pwr off board and rebooting board. An hour maybe 2 and it goes out ajax time out. So far no matter how many issues I've had none turned out to be user error. Nor has any wiring on machine related issue, been the cause. The pc being used only connects via ethernet. no usb. And has been online with internet for 342 uninterrupted days of service. Board looses connect every day. This is a static ip like the other 8 connected devices. It's number 3 on router. Route has it's name and stored its address and port. Is there a time limit for the interface? If so How do I disable that feature.


  • Banned

    ajax disconnects all the time now


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