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  1. #1

    Bed Not heating any longer

    All,I have a Monoprice Maker Select 3D Printer V2 unit. Long story short it was a basket case when I got it from a relative who gave up on it.The relative did a lot of replacement upgrades but finally ended up going to a more advance printer.I gladly took it off her hands and set the unit up and "leveled" the bed etc. I got it to the point I could pick 3D Print and print it. On occasion I would get a bad print but for the most part I printed about a dozen or so good size prints (say 30-40 hours of good printing) over the past 6 months. I was on a 9 hour print that was 2 components to hang my Netgear ORBI Satellites on the wall. The first one came out very decent and I was moving on to the second. It was running and about 2 hours in I got a thermal runaway errror which ended the print. I shut everything down and left it for the night. Tried again in the morning and the bed appears not to be heating and it will end up with the thermal runaway warning after a set time.I guess my questions are I am assuming it is a thermistor. How do I know its a thermistor versus a heat bed? If I used my DVM (Digital Volt Meter) and did a Ohm reading between the wires would that tell me if the thermistor is good or bad...would it be commonly be open on failure or would it fail in some other method?Should the heat bed be getting any voltage on initial start to preheat? (I assume its DC what voltage?) If it turns out to be a thermistor where is a good place to buy? Will any thermistor basically work? I see there are "generic" or this fits most 3d printers 100K thermistor. Better ones?Lastly, As the changing of this part could be more efficient by cutting/adding a connector that is external of PSU unit but before the bed a considerable amount. Basically avoiding the bed movement stress on the new proposed connector but at the same time reducing the changeout. (Not having to get into the PSU unit). Has anyone tried or considered this change?Thanks for the help,Chris

  2. #2
    Engineer-in-Training
    Join Date
    Aug 2020
    Location
    United Kingdom
    Posts
    250
    If you measure the resistance between the two wires of the thermistor you should get either 10K or 100K Ohms at room temperature and if you warm it up by putting a finger on it the reading should go down. Disconnect it from the main board first though

  3. #3
    Technologist
    Join Date
    Apr 2021
    Posts
    185
    Common point of failure for this model, IIRC, is the mosfet or the terminals at the board dying. It's a 12v system so there's a few amps going through the wires.

    If the bed thermistor shows a sensible value when it's at ambient temp (e.g., 20ºC), then it's probably ok. Move the bed around a bit and check whether it shows any fluctuating values. If that's ok, then follow the main heating wires back to the printer and see if you can find out where it's failed.

  4. #4
    Just wondering, can failure of one amp lead to malfunction of whole system?
    Last edited by Arnkatla; 07-24-2022 at 04:50 PM.

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