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[Solved] Preheat Error Bed  

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jimmyvinsane
(@jimmyvinsane)
Eminent Member
Preheat Error Bed

I had my heatbed fail the other day and bought a new one off Amazon.

After installing it I now get a "Preheat error bed" code when I attempt to go above 85c, I have printed with PLA a small test piece and it did fine but when I tried to print with some PETG using an 85c bed temp it gave me the error message.

I installed the old Prusa thermistor from my old heatbed and the problem was still there when I tried to heat it up again.

I don't know if buying a Prusa made heatbed will cure the problem, could it be something else besides the heatbed causing the error. Having tried 2 different thermistors would rule out that being the cause wouldn't it?

Any advice is appreciated.

Posted : 19/11/2021 1:50 am
Chicago Keri
(@chicago-keri)
Estimable Member
RE:

Here's some ideas..

Assuming you are running a Prusa Mk2.5s  or even a Mk2s.  These systems are more prone to heatbed issues as they are 12v system that run at higher current than the 24v Mk3 systems.

The non-Prusa heatbed is probably OK, though make sure that it is a 12v bed, not a 24v.  A 24v bed run on a 12v system will not provide enough heat.

Most likely, you are not getting enough power to the heatbed.  Likely fail points are the heatbed wiring, the connector at the MiniRambo for the heatbed, the connectors at the MiniRambo going to the power supply, the power supply wiring, and the connections at the power supply.

A common fail point is for the connector at the MiniRambo to develop a poor connection which will often melt the connector housing. In some cases it can damage the MiniRambo itself.  If you are lucky, tightening the setscrews in the MiniRambo power connectors might solve your issue.  

If the problem is not easily seen, you will need a voltmeter for further testing.   The power supply should be providing about 12vdc to the MiniRambo power connectors (there are 4, two positive, two negative).  With the heatbed cooled down and the system set to preheat, the MiniRambo should be outputting close to 12vdc. to the heated bed connector.  At the heated bed itself, the LED should glow brightly and there should be nearly 12vdc at the terminal bolts.  If you have considerably less than 12v, say 7v or 8v, the bed will not heat adequately.

There will be some voltage drop through the MiniRambo and through the wiring, and as the bed gets close to the set temperature, the system will reduce the power applied to the bed. 

Hope this helps...

 

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Posted : 22/11/2021 2:10 am
jimmyvinsane
(@jimmyvinsane)
Eminent Member
Topic starter answered:
RE: Preheat Error Bed

Thanks Chicago Keri,

I just got my new Heatbed from Prusa and hooked it up and all things work properly.

Posted : 26/11/2021 8:00 pm
jimmyvinsane
(@jimmyvinsane)
Eminent Member
Topic starter answered:
RE:

My problem seems to have returned, I have been printing ASA all week and Friday morning I tried to print and got a bed preheat error when the bed temp hit 90C.

I thought I had a work around by going into the settings - temperature - bed and set it to 105C  and it heated up fine and then loaded the g-code for the print and it worked all day by doing that. The next morning I tried to print again and nothing would allow me to get the bed up to temp, I don't have any problems printing PETG at 85C but trying to get much over 90C and I get the preheat error.

The heatbed is brand new Prusa heatbed which fixed my original problem of a dead heatbed but now this.

What should I try next, getting tired of all the heating errors with this printer.

This post was modified 4 months ago by jimmyvinsane
Posted : 24/01/2022 12:43 am
Bob
 Bob
(@bob-2)
Reputable Member
RE: Preheat Error Bed

Could there be a draft near the printer that cooling off the bed? 

I have a problem when I try to print ABS, my bed can't maintain the heat and my print fails with a thermal error.  My solution is to not print ABS during cold weather and since I discovered PETG I haven't needed to print ABS at all anymore.

If it is a draft you may be able to deal with the problem by covering the printer with a large cardboard box that will retain the heat during the print.

Regards

-Bob

Prusa I3 Mk2 kit upgraded to Mk2.5s, Ender3 with many mods, Prusa Mini kit

Posted : 24/01/2022 6:54 pm
jimmyvinsane
(@jimmyvinsane)
Eminent Member
Topic starter answered:
RE: Preheat Error Bed

I have the printer in an enclosure so no draft problems.

I looked at it again today and found the power lines from the PSU had melted a bit again, I looked at the heatbed connections earlier and all was fine and when I have to remove the printer from the enclosure I need to unhook the PSU from the printer to get it out and found the melted connections. I replaced both molex connectors when I installed the new Heatbed a month ago.

The problem seems to be solved with a replacement of the PSU connectors, after seeing how many people have troubles with this I guess I will have to find some better way to make the connections because the original design seems to have a flaw in it.

Thanks for the reply.

Posted by: @bob-2

Could there be a draft near the printer that cooling off the bed? 

I have a problem when I try to print ABS, my bed can't maintain the heat and my print fails with a thermal error.  My solution is to not print ABS during cold weather and since I discovered PETG I haven't needed to print ABS at all anymore.

If it is a draft you may be able to deal with the problem by covering the printer with a large cardboard box that will retain the heat during the print.

Regards

-Bob

 

Posted : 25/01/2022 12:38 am
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