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Solved Another robo 3d bed not heating up

Discussion in 'Troubleshooting' started by mamejay, Feb 20, 2016.

  1. mamejay

    mamejay Member

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    Hello everyone.
    I just got my hands on a second have robo 3d v1 today. I managed to get a couple of basic prints out to test and was very happy.
    I have gone to do a 3rd and I am finding that the flat bed is not heating up.
    Coming up as 0 degrees.
    I have checked the terminals and found that 0 volts is being read.
    I have read other threads mentioning to check the fuses. Where are these?
    Also anything else I can check?
    My friend sold me this so it's not like the seller was palming off a lemon.
    Thanks
     
    #1 mamejay, Feb 20, 2016
  2. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    There is no standard FUSE to the bed heater. There is a polyfuse on the RAMPS board (this is not a standard fuse) for the output port that powers the bed (the one you are reading 0 volts on). It is normally not the polyfuse that dies however, it is normally the output MOSFET (Q3). If you are up to it you can swap the MOSFET, or try a new RAMPS 1.4 as they are relatively cheap (and make good spare parts).

    RAMPS1_4schematic.png
     
    #2 mark tomlinson, Feb 20, 2016
    mamejay and Geof like this.
  3. mamejay

    mamejay Member

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    Thank so much for that. I have checked the schematic and the part is a STP55NF06L
    Is there any other equivalent type that can be used? My local parts place only has a few other types. I just got the printer and don't want to wait for the parts to arrive :)

    **EDIT**
    OK. I have done a swap of Q3 and Q1 and I still have the same problem. No voltage.
    Would be be a faulty RAMPS board? If so I will just order a replacement.
     
    #3 mamejay, Feb 20, 2016
    Last edited: Feb 20, 2016
  4. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    It certainly could be. While Q3 is the usual suspect it would not be the only one :)

    I have done both. I keep spare RAMPS boards around for a quick fix and I have swapped the MOSFETS as well.
     
    #4 mark tomlinson, Feb 20, 2016
  5. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    I personally prefer replacing them with the FDP8870, or the IRLB8743's
     
    #5 mark tomlinson, Feb 20, 2016
  6. mamejay

    mamejay Member

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    OK. I have ordered a new ramps board just in case.
    Just a question. Should the bed ambient temperature show up with something and not just zero? When I switch the unit on the print head shows 23 degrees but the bed is zero.
    I swapped the thermistor's over for the head and the bed and still it showed zero. This is worrying me now.
    Also with the replacement bed is it just a matter of changing it over an nothing else needs to be done?
    Thanks
     
    #6 mamejay, Feb 22, 2016
    Last edited: Feb 22, 2016
  7. mark tomlinson

    mark tomlinson ༼ つ ◕_ ◕ ༽つ
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    Yes, the bed should show ambient if the thermistor is connected and working correctly.
    On both of mine they actually read the same if I have not been printing.
     
    #7 mark tomlinson, Feb 22, 2016
  8. mamejay

    mamejay Member

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    Well tonight I had another look closer at the thermistor. There must be a problem with it as I lifted the bed and pressed down on the wire look at the temp came up!! I suspect that it will be needing to be replaced.
    Any ideas what I need to get my hands on?
     
    #8 mamejay, Feb 23, 2016
  9. mamejay

    mamejay Member

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    Just an update. I have found that halfway down the cable there was a break. Only found it by piercing it with my meter it 8 isolated the problem. Cut and fixed the area. Now no more bed thermistor issues
     
    #9 mamejay, Mar 25, 2016
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