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I'm hoping I'm wrong, but I think my RAMBO burned out. I've had a functional printer for several weeks and was starting to get some really good looking prints out of the machine, but today the bed temperature was reading -2.75 or so in Repetier Host. The Extruder reading was proper room temperature, and they're usually both the same when the machine is cold. I hit the button to heat the bed and it appears to be functional - temp is just ~27C lower than it should be. I checked the solder and the connection to the board, both look OK. So, I tried a test print and the extruder motor never moves.

I shut down both the printer and the PC, powered both back up, and tried using the manual controls to extrude or retract 5mm... nada. Absolutely zero function. No noise, nothing. I pulled the filament out, still no movement. I can manually turn the motor with my hand so it isn't seized.

I tried swapping the Extruder plug on the RAMBO to one of the axis motors and manually moving the motors a few mm... the extruder motor *does* move then. This tells me both the wiring and motor are OK, and the issue is with the extruder output on the board. To test this, I connected an axis motor to the extruder plug: no response there. That output is dead.

So, I think the RAMBO is dead... not a good lifetime on that component if that's the case, and I'm not liking the replacement cost.

Could someone recommend some more troubleshooting steps before I start throwing money at this thing? I get no errors at all and watching echo commands in Repetier just looks normal, the command to extrude 5mm is sent and no error is shown ever.

UGH. Thanks in advance, I've gone from ecstatic to completely frustrated here so I hope I don't sound too glum. The machine had been working so well lately and now it's no more than a paper weight!

Bed temperature indication sounds like a bad thermistor setting, or just a bad thermistor (it's blown or something is wrong with the wiring.)

Dead stepper plug could be hardware failure, a blown fuse (remove and check them - there are two minuscule ones and a big automotive fuse), or pins.h is confused about which board you have.

If your fuses are OK and you haven't upgraded/modified the firmware or EEPROM settings, you might want to email SeeMeCNC about it and ask if you can RMA the board. They might also have some ideas.

Thanks for the suggestions! I wasn't aware of the two smaller fuses, but checked them and wasn't able to discern much. Neither is visibly burnt or damaged in any way, but they aren't transparent so I don't know how they look inside. The big 15A fuse is OK for sure.

I tried swapping the 2 thermistor connections and the negative value stays on the bed, so that issue is probably neither thermistor nor wiring, but appears to be the thermistor output as well. Unplugging the thermistor entirely gives a solid -20 value (I believe, not looking at it now) so there *is* a difference and the port isn't completely dead.

I had not made any changes to settings, config, or firmware since my last successful use of the printer so it is sounding like a hardware malfunction. I did email the seemecnc support@ address yesterday so hopefully they'll get back to me soon. Should I try calling, or are they typically quick to get back? I know with orders they're typically very quick so I'm not worried about that, but do you know if this would be warranteed? I ordered my printer in mid-june and a lot of the time warranty only applies for 30 or 90 days, and unfortunately I spent that time building the printer. We'll see when they get back to me, though. I've had nothing but positive experiences working with the seemecnc staff thus far.

Is there a newer firmware than 0.80 available? The Repetier my printer is based on has had several newer revisions released, but I want to stick with a 'factory' firmware considering how well she was printing before it died. Could I try another host application, perhaps? I can't try printing direct-from-usb without a computer, as the printer is going into a reboot loop when a card is inserted into the SD card slot, and doesn't stop rebooting until the card is removed.

To check the fuses you need to pop them out and check with a multimeter to be sure.

626Pilot wrote:Bed temperature indication sounds like a bad thermistor setting, or just a bad thermistor (it's blown or something is wrong with the wiring.)

Dead stepper plug could be hardware failure, a blown fuse (remove and check them - there are two minuscule ones and a big automotive fuse), or pins.h is confused about which board you have.

If your fuses are OK and you haven't upgraded/modified the firmware or EEPROM settings, you might want to email SeeMeCNC about it and ask if you can RMA the board. They might also have some ideas.

From the Rambo Wiki:
Power

Three independent power rails for flexible input power configurations
Heated Bed, 15A 12-24V (version earlier than 1.1 limted to 14A 16V due to fuse rating, see rambo_development for hacks)
Extruders and fans, 5A 12-24V (fuse can be exchanged for up to 10A capacity) 10V-26V input voltage
Motors and logic, 5A 12-24V (fuse can be exchanged for up to 10A capacity) 10V-26V input voltage


If the fuse for the motors and logic opens, it should effect ALL motors. If he swaps a motor from a suspected bad driver to a different driver and the motor works then the fuse
should be fine. Anytime a motor that is not working is swapped to a different driver port and the motor then works it pretty much indicates a bad driver port. Then the question
arises, I have been running fine for weeks then suddenly a motor stops working, how can that happen? It could be just defective electronics but my bet is on defective wiring.
When the machine is operating fine, it is likely flexing the cables where they plug into the driver ports on the Rambo. If the flex is enough and the crimps are not done properly
a brief open or short can occur and with the power on and that happens it would be the same as pulling the motor connector out with the power on and the resulting blown driver
port. I would always recommend that if a driver becomes defective before replacing the Rambo the user should very carefully check those crimped connections on the motor that
quit working and also check the crimped connections on ALL of the motor connectors, if one was bad there is a good chance that they are all suspect. This is just my humble
opinion and I placed it here to help users understand why a motor driver can all of a sudden become defective.

Following up, this issue appears to be a bed-thermistor port issue entirely. The extruder motor is disabled when the bed temp reads below zero, so this is a safety mechanism. The bed itself is completely functional, it simply reads 27C below what it *should* be reading. If I heat the bed to my desired temp (-27) and then start a job, it does print OK, as a test cube was printed in the way specifically to test the issue. I have now tried three thermistors on that port (including a borrowed unit that was never installed into the printer - just plugged in and left the wired dangling out the door) and all three work fine reading ambient temp via the hotend port, but all three also read ambient -27 on the bed port.

So, I'm either leaning to a slightly failed RAMBO that is merely not getting a proper read on ambient but *does* work as long as you preheat the board to [desired_temp-27], or a setting somewhere that is telling the board to reduce the displayed value by that 27C. has anyone seen such a setting? I haven't found it, and never did this intentionally, but who knows if I might have entered something incorrectly when sending a G28 or an "m42 p6 s255" command.

Thanks!
Bry

Is it possible that you used a different thermistor for the heated bed? I *think* the thermistors shipped by SeeMeCNC are NTC (negative temperature coefficient) which means they decrease in resistance as temperature increases. And also, the thermistor for the hotend is ~100K but the heated bed is ~8K or something like that. Which means that if you have a 100K thermistor plugged in where the RAMBO + firmware expects an 8K, it's going to give you a negative temperature.

Anyway, that's kind of just a guess. There are other folks on the forums here that are more experienced than me and might know otherwise.

dpmacri wrote:the heated bed is ~8K or something like that

Confirmed, mine says 8.9K at room temperature.

I suppose it's possible, but it's from a friend that is planning to start his MAX clone of his own so he's been buying identical parts to the ones that came in my kit, and it returns the exact correct values that the original two show when connected to the hot end port. We just used that because it was available and it was a way to make sure my wires weren't shorted somewhere, and the fact that it's no different was all I was looking to find out. If he had a RAMBO yet I'd have tried wiring my thermistors up to see if one made the error on the other bed port.