Bed not heating/holding temp

Greetings,

I work in a library, and we have two lulzbot minis. Worked great for the majority of the time we’ve had them, but both have developed some issues.

One printer wouldn’t hold objects on the print bed. I figured it was the PEI sheet, and went and changed it (freeze, scrape, reapply, cut to size). This doesn’t help the problem. I look at the temps and lo and behold, the printer isn’t heating up. I pull the bed out and use our multimeter to see if there’s a problem with the print bed, one connection says it isn’t completing. We order a new bed. Hook it up, no dice. Still won’t heat up. I opened the case and ran completion tests and the Mosfet wire is dead (will replace later).

The -Second- printer was incrementally dropping temp during the print. It’d be at maybe 80 degrees max, and then slowly keep dropping. Swapped build plates, did the same thing. Let the machine be a bit, fired it back up wanting to see if it held the temp while not printing ok or not, and now the bed won’t heat at all either.

Originally I was thinking that the second printers issue was software, that maybe someone fiddled with a profile, or an advanced setting or some such. I have not opened up the second printer to test for dead wires yet, but it literally just came back from maintenance (bad y-min sensor) about two weeks ago…

I’m at my wits end, any one got any ideas?

Update: I went and powered down the printer, disconnected the Mosfet connection on the bed, reconnected it, and started the printer up again and it will heat up again, am now testing to see if it will -hold- the temp for an extended period or not.

The bed power cable inside the chain has broken 2 times in my printer. The symthoms were similar to what you are describing because it keeps making contact sometimes and sometimes not.

You may be experiencing two separate problems. Th first one does sound like a broken wire on the inside of the electronics box or a wire not screwed tightly to the terminal block connector inside.

The second one sounds like a software issue i experience once when i was using a Lulzbot mini at my local library. It too would occasionally do weird things and slowly drop the temperature. I think it was some sort of software bug. The Machine happened to be on a MAC but other than that i was never able to document the behavior enough to report it. Try updating your cura software and maybe also updating the mini firmware once you download the latest cura. See if that helps.