BED PREHEAT ERROR was a toasted fuse
My heated bed stopped working after an attempt to calibrate the temperature. Returned to find BED PREHEAT ERROR. Talked to chat and pointed me to check fuses again. Yes it was a charred bed fuse but also the LED was melted like a fuse too. Replaced the fuse from my emergency kit in my car but the LED is another matter. But perhaps I should start to find out what causes the melt-down.
What is the LED and can I replace it?
What tips other than found on https://help.prusa3d.com/en/article/multimeter-usage_2117 should I do to find the source of the over-voltage/current at the fuse?
Thanks guys!
MK2S kit owner since 8/15/2017
RE: BED PREHEAT ERROR was a toasted fuse
Sorry, here is the picture using forums own server.
MK2S kit owner since 8/15/2017
RE: BED PREHEAT ERROR was a toasted fuse
Test print worked well. Second PLA print failed due to Bed thermal runaway. Out of ideas.
MK2S kit owner since 8/15/2017
RE: BED PREHEAT ERROR was a toasted fuse
Went though https://help.prusa3d.com/en/article/multimeter-usage_2117.
Just for academic purposes...
- Hotend heater resistance, 3.4 kΩ, within spec.
- Bed heater resistance, 0.8 kΩ, within spec.
- Hotend thermistor resistance (not relevent)
- Bed thermistor resistance at 19°C ambient, 121 kΩ.
- Rambo shows 11.25V at both heater headers with no load.
- Rambo shows 11.55V at both heater headers with extruder heater connected only.
- Rambo shows 11.55V at extruder but 3.1 mV at the bed heater when both heaters are connected. Also, when bed heater is connected a red LED on the Rambo turns off. If the bed heater is unplugged, the bed's receptacle returns to 11.55V with the LED turning back on.
I resoldered the LED which was working for the one PLA good print I got from replacing the 15 Amp blade fuse for the bed heater. The LED was working perfectly for that one so I don't think it is a resoldering issue.
Any help? I need to print MK3 parts.
MK2S kit owner since 8/15/2017
RE: BED PREHEAT ERROR was a toasted fuse
Conclusion for LiveChat is a failing power regulation on the RAMBo 1.3. It is discontinued so this may be the end of the road for my MK2.5S unless I can repair myself but what is wrong and what can I reflow/solder? Which MOSFET which capacitor? I'd prefer not to go on a wild goose chase when I need a working printer by February. It would seem this board is a bit of a ghost town as well so this note in a bottle will be left to float but I'm moving forward with an upgrade or new printer...might not be a Prusa.
MK2S kit owner since 8/15/2017
RE: BED PREHEAT ERROR was a toasted fuse
Note that a couple of people have replaced the Mini Rambo with the Einsy board. One post I saw said that you could use a 24 vdc wall wart for the 24 v, and continue heating the print bed with 12v.
This is not the post I am thinking of, but it is related. He is running stock MK3S firmware:
https://forum.prusa3d.com/forum/original-prusa-i3-mk2-5s-mk2-5-hardware-firmware-and-software-help/einsy-rambo-on-mk2.5/
Chris Shaker
RE: BED PREHEAT ERROR was a toasted fuse
This is the post I was thinking of. First I saw where someone upgraded a MK2 to the Einsy board:
https://forum.prusa3d.com/forum/original-prusa-i3-mk2-s-hardware-firmware-and-software-help/einsy-rambo-on-mk2/paged/2/
Chris Shaker
RE: BED PREHEAT ERROR was a toasted fuse
Posting as I opened the bottle myself years later. Prusa might not have in stock the board but their supplier UltiMachine still carries the board for the MK2 to the date of this post. I’m up to my third Mini-Rambo 1.3 at this point but am still printing and running off the latest stock firmware. Still don’t know why my set up keeps blowing out heatbed circuits while leaving the fuse intact but $100 every several years in “maintenance” cost is acceptable until printer tech truly surpasses i3 design…core XY is looking promising but this penny pincher ain’t biting if MK2 keeps printing well.
MK2S kit owner since 8/15/2017
RE: BED PREHEAT ERROR was a toasted fuse
That is very weird that your board keeps dying. I'm still using the original one that was in my MK1. I rebuilt it into a MK2, upgraded it to a MK2S, and now have upgraded it to a MK2.5S+ in a Bear frame.
Chris
RE: BED PREHEAT ERROR was a toasted fuse
Am on MK2.5S myself, Heatbed voltage is 11.1V, a little low but within spec. Heatbed resistance unplugged is 1.1 Ω which is also within spec. Yeah, don't know why the connector melts eventually, then when soldered directly, fuse pops eventually. Can't be AC, the MK is hooked up to a 1500VA UPS with voltage stabilization. MK is in a heated chamber kept at 110°F (43.3°C) when printing hot materials to take some load off the bed so that can't be it. I was half tempted to go headless in chamber but Rambo specs say it can handle ambient that hot. Power supply not so it has been relocated outside. Gremlins, definitely gremlins.
MK2S kit owner since 8/15/2017