Bed preheating error  

Re: Bed preheating error

check for continuity in your heatbed power wires

it's likely one has broken...

regards Joan

Re: Bed preheating error

I've continue the testing.

The cables to the bed is OK. The resistance is 2.7-3 ohm.

I loosen the cables from the motherboard and run the bed with 12 V at right polarity. The termistor indicated a slow rise in temperature. I didn't have 24 V available but the principle showed the heat bed and its cables and termistor were working. The red LED also light up.

After long rest the bed heating from menue in printer made it possible to pre-heat and the red LED shine according to its control algorithm. When it was light I could measure almost 24 V, say 23.2 V.

The hot end/extruder heating is working.

Then I started to re-calibrate the system the red LED didn't light up, neither it was any voltage.

As far as I can understand it there are two reasons left. Pls, correct me if I'm wrong.

1/ There is some fault in the power supply.
2/ There is some fault in the driver stage in the motherboard.

What to do next? Warranty issue?

Re: Bed preheating error

Did you ever resolve this issue? I've got the exact same symptoms. Heatbed cables are good, reseated and continuity tested. Thermistor responds perfectly to heatgun and the adheasion to the underside looks proper. Printer can heat from a long rest but will lose heat 5 or so minutes into the print and will error to "thermal runaway". Is not able to thermally re-calibrate ever.

From day one my printer psu had a pretty loud clicking noise in sync with the heatbed light. Reading on the forums that seems common, but I am suspicious of it.

Re: Bed preheating error

hi Dabigw,
if you turn the preheat on, say PLA
watch to see if the LED by the cable connector cover, comes on...
the LED should be solid red until the bed is near proper temperature.
as soon as it starts heating, move the Y axis fully forward and fully backward, slowly, a couple of times. if the LED flickers or goes out, you either have a faulty cable, poorly seated heater connector, or loose connection between the wires and the heatbed. early mk3 printers had the wires soldered directly to the heatbed,

Mine broke a wire off at the soldered joint, on the heatbed.
some people suffer loose connections on the Einsy,
some people suffer stress fractures within the cable itself
it's very uncommon, but possible that the einsy goes faulty

while moving the heatbed, if the LED doesn't flicker, when it shouldn't... watch the LCD Temperature reading, it should change temperature slowly, if begins to rise, then drops to a very low reading or flickers, you have a problem with the thermistor,

if you get any of these symptoms, try and identify the cause, and resolve if you can, if you can't resolve the issues, have a word with prusa support, on the chat service found at the bottom right of this page >>> https://shop.prusa3d.com/en/#_ga=2.136444976.1615854133.1544998168-1020553264.1515166609

regards Joan

Re: Bed preheating error

I ended up reaching out to prusa support. I did some more testing and confirmed that it was not an issue with any sort of connection with the machine. Triple checked connections and did continuty testing from the bed to the Einsy at various positions on the Y axis. I put together a little video that outlines the exact problems of my machine and does a bit of trouble shooting. I believe it to be a hardware issue at this point and I’m waiting to hear back from prusa support.

Here’s the video in case anyone is interested.

Re: Bed preheating error

What are the voltages reported in the support menu DURING bead heating? Bed voltage report should be 23.6 to 23.7.
If the bed voltage is dropping below that, I would suspect low power supply voltage or terminal connection losses at the EINSY.

Check output voltage with a multimeter at the power supply. Its output voltage can be adjusted via a pot inside the power supply, but be very cautious about going over 24 volts.

Re: Bed preheating error

Thanks for the suggestion. Voltage reading from the printer itself was way low when preheating. Around 22V. Got that same reading from the einsy terminals so I dug into the PSU enclosure to get a reading from the PSU terminals itself and found the issue

Second terminal in was almost entirely unscrewed, blackened, and partially melted. This was all inside of the black PSU housing that is assembled from PRUSA. I hope it became loose during shipping and not due to poor assembly. This sort of issue could easily burn a house down...

Re: Bed preheating error

My thermostat wires broke off at the place where they are soldered onto the main wire under the heatbed.

Is this something that I can fix by re-soldering? Should I contact Prusa support? I see that Joan above had this issue - how did you resolve?

Thanks for any help!

Re: Bed preheating error

Hey, I found the same problem with my PSU:

It is also the second terminal.

RE: Bed preheating error

I had a "bet thermal runaway" and "bed preheat error".   It was the a loose screw terminal shown by dabigw above.  Tightening the screw terminals solved the problem - an easy fix!  

RE: Bed preheating error

I had a "bed thermal runaway" and "bed preheat error".   It was the a loose screw terminal shown by dabigw above.  Tightening the screw terminals solved the problem - an easy fix!  

RE: Bed preheating error

I had a "bed thermal runaway" and "bed preheat error".   It was the a loose screw terminal shown by dabigw above.  Tightening the screw terminals solved the problem - an easy fix!