Heatbed Not Reaching Temp

If you are having issues with your heated bed not hitting temperatures, please try the following:

Damaged/Exposed Traces

The first and easiest thing to do is visually inspect the heat bed surface. Check areas where you may have had nozzle crashes or can see deformations in the PEI surface. If you see any of the exposed traces or copper layers of the heat bed interior, this is the likely root cause of your heating issues.

IPA Test

To see whether the surface is heating properly or at all, we suggest wiping down the heat bed surface with Isopropyl alcohol (IPA) cold and then preheating. The alcohol will evaporate when heated, exposing areas that are not heating at all.

Loose thermistor

Simply look in between the heated bed and the Y carriage to see if the thermistor has come loose.

The heated bed thermistor should be secured like so to the underside of the heatbed. 

Not the two types of tape securing the thermistor. There is a layer of aluminum foil tape underneath the layer of kapton tape.

If you notice the thermistor is hanging freely, unattached to the bed, undo the 6 bolts holding the bed to the Y carriage and re-secure the thermistor.

Loose thermistor

Loose power connection

If you inspect the thermistor and find it is secure and attached firmly, it's time to inspect the cables.

Remove the printed cover at the back left of the heated bed. Inspect the leads supplying power to the bed coming from the electronics. Are the wires damaged at all? Follow this lead back to the electronics, carefully inspecting for any damage along the way.

Next, open the electronics enclosure and make sure that the heated bed connector is securely seated to the Rambo Mini (you should do this periodically as part of printer maintenance!).

Last connection to check is the input voltage lead coming from the power supply (PSU). Check to ensure that the plug is secured and follow the lead to inspect for any damage. Look at potential pinch points where you have ziptied the wires to the leadscrews.

**Please try the following if you have access to a multimeter to get some data to see if the heatbed components are out of spec or potentially problematic.**

If you are unfamiliar with how to use a multimeter, here is a good tutorial you can look over.

Measuring resistance:

  • The resistance of the heated bed thermistor should be approximately 100K at room temperature (same goes for the thermistor on the hot end if you are curious!)

  • The resistance of the heated bed should be 1 ohm (don't worry if the resistance oscillates around 1 ohm)

Measuring voltages:

  • The voltage coming to the heated bed should be ~12V
  • The voltage coming from the PSU to the Rambo Mini should be ~12V too.

If the issue persists after trying all the above, contact our support team at info@prusa3d.com. Be sure to include the fact that you've tried the above steps and any measurements you may have obtained.

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