Hi all, we’ve been using v1.4 Rambos to power MPCNC’s and TAZ 3D printers at our Fab Lab for quite some time now. Recently the Rambo blew out on my TAZ5 at home and I ordered a new one to replace it. Upon installing it tonight and testing all the wiring (thermisters, steppers, limits, fans all work fine) I noticed the bed heater won’t work. I’ve tried the following so far:
Replacing bed heater fuse
Checked continuity on bed heater wires, replaced mosfet plug
Tried another bed from a working printer
Installed older firmware (2017) was using latest prior
Created entirely new wire connection to bare contacts on bed
Attempted to heat bed from extruder socket (blew F3 fuse, replaced it, decided this was dumb)
Wired bed heater mosfet directly into multimeter, gets 2V consistently when powered (should be 24V)
It’s got a 120mm fan right on it so it should be cool. Red light turns on when heating as it’s supposed to. 400W power supply worked fine taking the bed up to 85* + in the past. I’ve been crawling forums looking for folks with similar issues and most of them find burned out parts, of which I can find none.
Any suggestions? I’m out of ideas. Do these things come with a warranty? It’s a few weeks old but I just took it out tonight. Thanks in advance to anyone who can help!
Compare the + and a ground somewhere else. That should be 24V. When the heated bed is off, the minus is floating, but when it is on, it should be ground.
As for fan 0 and 1 being connected… I can’t believe I did that. I don’t remember why I did that, and it is clearly very stupid. I think it was from troubleshooting with a dual extruder (it’s not currently plugged in nor does the board have the dual extruder firmware) a while back. Just pulled the 2nd one out. I knew I was being an idiot somehow, thank god I never turned that socket on. Thank you for pointing it out. Bed heat still doesn’t work
Checked the F4 fuse first thing… BUT - I should have thought to replace the power connector. It looked fine but I replaced it anyway just now - and it works! I think! Thank you!!
Pardon me for asking what might be a very silly question. But why not simply switch this Rambo board out for the one on your MPCNC? Most MPCNC’s don’t need to use bed or extruder heaters anyway. Since that board works fine why not use it in the TAZ?
