MakerGear Forum

This is what happens when you stop printing everyday, things get stuck and fixing them just makes things worse. I tried to get NinjaFlex to print, the extruder kept getting jammed, I tried cleaning filament, and it didn't go through. Ended up taking the whole head apart cleaning it (including replacing nozzle and cleaning the hotend tube just to make sure).

While assembling things back the machine died on me - extruder fan stopped working. [Yeah, in retrospect I should turnoff things before (dis)assembly ]

Turning off & on I can hear the power unit fan going on, but the two printer fans (extruder and motherboard) do not turn up nor any of the leds.

Suggestions?

Check fuses. That's the usual problem when the RAMBo appears to be dead as a doornail. There is one automotive-type fuse in the back, but there are also I think three small fuses on the board that look like surface-mount devices. Go to the RepRap website for the RAMBo and look for mention of the fuses in the documentation. If you have an ohmmeter, it should be easy to figure out if one of the fuses has blown.

Hi Tim,

I found two small (tinyfuse) fuses. Replacing them returned my printer to life. BUT,... as I was checking it, I noticed that one head (the one I was fiddling with when this happened) started to heat up. Before I could connect to the printer to see what it was doing, the fuse burned. Went through the following steps:

* Replacing the same fuse (the one for the nozzles and fan according to online search), and turning the printer lead to immediate fuse snap.

* Disconnecting the problematic head, and restarting, things seem fine. However, I did not manage to control temps on the second head or the print bed.

* Connecting my spare head instead of the problematic one, the printer turns on, but this head starts heating like crazy. Trying to set it to off from octoprint did not work "M104 T0 S0.000000" was basically ignored. I turned the printer off before the temp got too high (which I think is what went wrong in the first attempt).

So, can it be that the board firmware got screwed up in the process? (How do I reset it?) or is it a hardware problem?

Thanks again!

Nir

Maybe a thermistor issue?

jsc wrote:Maybe a thermistor issue?

Explain?

Thermistors are delicate with thin wires, and can fail in a mode where the firmware thinks it's not heating when it actually is. I forget if that is failing short or failing open....

Anyway, it's a possibility, but I thought there was code in Marlin to try to prevent thermal runaway like that.

jsc wrote:Thermistors are delicate with thin wires, and can fail in a mode where the firmware thinks it's not heating when it actually is. I forget if that is failing short or failing open....

I think a failing open is immediately detected as an error. A failing short may end up registering as a negative temperature, which is why setting the temperature to zero wouldn't do any good. It would think that it still needs to heat up to get to zero. Just a guess off the top of my head, though.

Anyway, it's a possibility, but I thought there was code in Marlin to try to prevent thermal runaway like that.

I thought so, too, although I'm not sure what the method is. The firmware would have to notice that you were pumping current through the heater for some amount of time without the temperature changing. . . something like that. Possibly it would have detected thermal runaway eventually and hadn't quite reached the trip point when it was shut off. Not sure.

Regardless, it's almost certainly a hardware problem. The firmware is on the digital part of the controller board which runs on its own power supply at 5V (or maybe 3.3V). It's relatively well-protected from things that go wrong with the high-voltage analog parts. It sounds like the heater cartridge shorted on the first hot-end. That heater cartridge is probably shot, unless it's a matter of exposed wires contacting the heater block (which is actually a strong possibility since the head was disassembled). If the 2nd hot-end is having problems with the thermistor. . . did you (talking to Nir) perhaps not reconnect both the heater and thermistor on the 2nd hot-end you tried, or plug the thermistor into the wrong socket? The heater and thermistor are the two points of the feedback loop, so if either one is connected to the wrong socket, thermal runaway is the result.

Anyway, from the available evidence, that's my diagnosis: (1) heater wires got exposed while re-assembling the head; (2) heater wires touched the heater block and shorted the high voltage supply; (3) the fuse blew; (4) wires are still shorting, so the fuse blows every time that hot-end is plugged in; (5) 2nd hot-end was connected as an experiment but ended up with the thermistor plug in the wrong socket; (6) thermal runaway ensues when the 2nd hot-end is turned on.

Tim wrote: Regardless, it's almost certainly a hardware problem. The firmware is on the digital part of the controller board which runs on its own power supply at 5V (or maybe 3.3V). It's relatively well-protected from things that go wrong with the high-voltage analog parts. It sounds like the heater cartridge shorted on the first hot-end. That heater cartridge is probably shot, unless it's a matter of exposed wires contacting the heater block (which is actually a strong possibility since the head was disassembled). If the 2nd hot-end is having problems with the thermistor. . . did you (talking to Nir) perhaps not reconnect both the heater and thermistor on the 2nd hot-end you tried, or plug the thermistor into the wrong socket? The heater and thermistor are the two points of the feedback loop, so if either one is connected to the wrong socket, thermal runaway is the result.

Anyway, from the available evidence, that's my diagnosis: (1) heater wires got exposed while re-assembling the head; (2) heater wires touched the heater block and shorted the high voltage supply; (3) the fuse blew; (4) wires are still shorting, so the fuse blows every time that hot-end is plugged in; (5) 2nd hot-end was connected as an experiment but ended up with the thermistor plug in the wrong socket; (6) thermal runaway ensues when the 2nd hot-end is turned on.

One piece of information - the temp measurement on the head (new one at least) was correct. It was set to zero but registered rising temps (I killed a bit before 200C).

Regarding your question - I connected both plugs. I don't think you can connect the thermoresister the wrong way - these plugs (the ones with the clip that locks them) are designed so that you cannot do that.

Any other ideas to check? I will get a multimeter and then will check the shorting head part of the diagnosis.

Thanks again,

Nir

nirfriedman wrote:One piece of information - the temp measurement on the head (new one at least) was correct. It was set to zero but registered rising temps (I killed a bit before 200C).

I expect you to see a temperature rising on the graph. . . the question is whether it thinks the temperature it's reading is for the same device that it's trying to drive the heater on. But I admit that I'm not coming up with explanations that fit the evidence.

Regarding your question - I connected both plugs. I don't think you can connect the thermoresister the wrong way - these plugs (the ones with the clip that locks them) are designed so that you cannot do that.

They don't even have to have the clip---thermistors and heaters can be plugged in either way; they're completely bidirectional. But the RAMBo has three (four?) thermistor sockets and several heater sockets, and each thermistor plug/socket has to correspond to the right heater plug/socket.

Any other ideas to check? I will get a multimeter and then will check the shorting head part of the diagnosis.

The only other thing I can think of is that it may be that the power transistor has been damaged and is no longer able to properly shut off.

If you don't have a dual extruder, then you have the option of switching all the wiring on the controller board from extruder 0 to extruder 1, if the extruder 1 power mosfets are all in proper working order.

Tim wrote:

Regarding your question - I connected both plugs. I don't think you can connect the thermoresister the wrong way - these plugs (the ones with the clip that locks them) are designed so that you cannot do that.

They don't even have to have the clip---thermistors and heaters can be plugged in either way; they're completely bidirectional. But the RAMBo has three (four?) thermistor sockets and several heater sockets, and each thermistor plug/socket has to correspond to the right heater plug/socket.

I see the confusion, I didn't touch the RAMBO connection, only the connections on the printer head.

I have a dual-head, and when I remove the problematic head (tool 0) I can't control tool 1 (the printer is ignoring temp setting commands)...