BED THERMAL RUNAWAY
My printer has been printing for over 40 hours non-stop and working great. I loaded up another print and about 1.5 hours thru it went into thermal runaway at the bed. Ive replaced 3 connectors at the Rambo board (bed heater connection) and they all melt on the ground pin. After the second plug, I replaced it and added some dielectric hoping that would fix any connection issues at the plug, but it melted again. Now it wont heat at all. Does this sound like a short somewhere in the bed traces?? I checked continuity in the leads up to the solder points at the bed and all is good there. Thanks in advance.
Re: BED THERMAL RUNAWAY
I checked the resistance on the bed and its .9 ohms. not sure if thats correct or not.
Re: BED THERMAL RUNAWAY
That is a thereabouts correct resistance.
Unfortunately when this happens, the only really workable solution is to solder the cables to the underside of the RAMBo.
Do not attempt to unsolder/remove the burned out socket; it's very easy to damage the board.
The cause of this is a high resistance mechanical connection; could be the plug was not fully inserted or there was some crud on the connector. By soldering directly, you will remove two mechanical connections, both of which are potential failure points.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: BED THERMAL RUNAWAY
FYI: dielectric grease is an insulator not a conductor grease.
dielectric will increase resistance even more.
what you want is conductive grease.
now Conductive and Dielectric are both insulators however the conductive grease has fine particles of metal in it making it conductive.
in this case the best action is either direct soldering of the wires to the board(silver solder has less resistance) or changing the connector type to one with a different mechanical connection with less resistance(gold plated bullet connector good to over 30 amps)
video on dielectric grease:
“One does not simply use a picture as signature on Prusa forumsâ€
Re: BED THERMAL RUNAWAY
Thanks guys, I bypassed the connector and soldered to the back of the board and everything is working again! Knock on wood!