Can my old faithful Mini Rambo 1.3a serve me longer?
Hi everyone 😀Â
My poor Mini Rambo 1.3a board has been through a lot, and the bed heater pins on the board have finally given up.
I don't mean the plastic terminal block has melted or the fuse has blown - those have happened before and parts been replaced, as well as wires soldered directly to the board. I mean the pins no longer receive current when read by multi-meter, and no LED is lighting up to indicate that current is being sent to the pins.
This is a bummer because as a last ditch effort I did try the MOSFET mod (a bit of a brain fart considering, should have done the mod sooner), but with no 12v going to the pins, the MOSFET gate never opened.
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So! After trying my luck with Prusa chat support I thought I'd ask here - do I have any options left before the board becomes a very nice paperweight?
I have managed to successfully breadboard a circuit to control a 5v MOSFET using the part-cooling fan pins - controlling an LED brightness using the LCD menu fan speed control was amusing for a moment, but ultimately not a solution unless I was willing to dispense with the part cooling fan.
The MK2 to MK2.5 upgrade takes up quite a few of the remaining pins on the Mini Rambo - are there any viable pins left to control the MOSFET with? Could I do something like swap the left fan to other pins and use those to control the MOSFET? Does a pin need to be PWM capable to be a candidate, or can any pin be PID controlled with the right firmware modification? And lastly, I couldn't get a good read on fan pin voltages, are these pins 5v or 12v?
Hoping one of the great contributors here takes an interest in this, thanks in advance!
RE:
mini rambo fans are 12 volt.
heatbed power should be 12 volts when the printer is turned on, mosfet should pull -ve lead of heatbed to ground when active...have you tested the actual board voltage at the board? one of the wires to the heatbed might be faulty.Â
you should be able to take ground and the gate signal from the heatbed mosfet, and use those to trigger an external mosfet, taking power from the power supply
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Can my old faithful Mini Rambo 1.3a serve me longer?
Thanks Joan, great to hear from you! Yes that's the issue - no 12v to the heater pins.
I forgot to mention, I can heat the heatbed by connecting it to the extruder heater pins and then asking printer to heat extruder - there's nothing wrong with the bed or wires.
I can also control the MOSFET using these pins. But the heatbed heater pins themselves have no activity, no indicator LED, 0.3v maximum reading.
Thanks for confirming the fan pins are 12v.
My most viable solution at this point seems to be... there is one unused fan + and GND I could potentially control the MOSFET with, although these pins are currently always on. I am comfortable changing pinout and compiling firmware, but wouldn't know how to PID control those pins, if that is possible