Heated Bed Not Heating?

[Falk3r]

Rostock Max v2 was printing fine yesterday; today the bed won't heat. The set point registers on the control panel, but the heater LED doesn't blink and the bed doesn't heat. I've done some power cycling, tried a few different files, did some manual setpoint manipulation, no dice.

Where should I begin with my troubleshooting? Should I order a replacement heated bed? Is this a common item that requires replacement? Thanks!

[geneb]

Did you check the fuse?

g.

[Falk3r]

Thanks, Gene - can always count on you.

I have visually inspected the Rambo, no signs of damage. All connectors seated.

I removed the 15A heater circuit breaker, no visual signs of damage. Multimeter check shows continuity. 15A reinstalled.

The 2x 5A small white fuses look "fine"; would they be discolored (gray/black) if they blew?

When attempting to head, LED6 on Rambo flickers red. LED embedded in the heated bed does not light. Resistance across the exposed leads of the LED embedded in the heated bed measures 4.7 kOhms.

I have inspected the solder joints beneath the heated bed. All kapton tape is intact, no leads are loose. There is some slight oxidation on the soldered pads for the large power leads, but nothing that seems to be the source of the problem. I removed the kapton tape on the thermistor solder joints for a closer inspection; they seem "fine".

Power supply lugs look "fine".

What's would you suggest next?

[timskloss]

The set point registers on the control panel, but the heater LED doesn't blink and the bed doesn't heat.

Ok, so the controller is commanding the RAMBO to send current to bed. When you confirm the set point is registering on the display and it should be heating, check the output voltage to the ONYX at the RAMBO connector with a DVM. You can touch the DVM probes to the screws inside the connector.

If there isn't 12 VDC at this connector then you may have a bad RAMBO board or a bad fuse. There are two small mini fuses on the RAMBO and of course the big ATC type fuse. Look up the RAMBO users guide for the location.

[Falk3r]

When I was preparing to do some power-on testing and check the 12V line to the bed, the darn thing started working.

Did reseating the fuse do it? Maybe when I carefully jiggled the wires? Or it was enough love and attention to set the beast to happy...

In any case, thank you for the help. I'll be back in 2 weeks when it starts failing again.

[timskloss]

Double check the power leads on the RAMBO to the ONYX. You may simply have a loose wire. Try tugging them out of the connector first to see if they aren't tight. (with the power off)

[Falk3r]

Hmm, that might explain some recent print failures. After a number of hours, the print loses bed adhesion (much like if the bed were to go cold) and the print turns to spaghetti.

Are those power leads the 6x screw terminals at the top/left of the RAMBO board? If so, the wires are snug and the screws are tight. No apparent issues there.

[geneb]

I do what I can.

g.

[Falk3r]

In my most recent testing, the bed again wasn't heating. I jiggled some wires and it fired up. So there you have it, definitely some intermittent connection somewhere. Guess I'll have to tear this thing down and see what I can do to improve wire routing and terminations inside.

Unfortunately, during that test build I experienced a major clog, had to tear down my E3D-v6 hotend, and now it's failing to register heat above ~110C. Probably broke my thermistor/wires in the rework. I'll report back in a couple weeks after some intensive fixin'.

[Falk3r]

Quick status update:

I disassembled most of the electronics and inspected all wiring connections, and found this blackened and swollen wire at one of the screw-terminals on the top side of the RAMBO board leading to the heated bed.

[img]http://i.imgur.com/t8GkiQt.jpg[/img]

I figured this got loose (recently moved, machine was probably jostled around a bit), weaker connection meant the same current through fewer touching strands. Overheating, intermittent connection. Problem identified.

So I trimmed the damaged area out, restripped, tightened the screw back down, retightened all other screws, and fired it back up. Everything worked for a week, but last night I am getting "DEF" temperature readouts for both Hotend and Heated Bed.

Search results indicate I have shorting thermistor wires? How likely is it that both thermistors shorted at the same time, or does the "DEF" pop up for both regardless of which one shorted out?

[joe]

A problem with either thermistor will cause a "def" fault. Usually a poor connection somewhere.

[Falk3r]

I ohm'd out the hot end thermistor wires and they report <1 ohm resistance each with no interaction across lines.

The heated bed thermistor wires report <1 ohm resistance each, but have a ~150 kohm resistance between the two which seems low. Right? Shouldn't I be expected > 10Mohm?

[EDIT]

OK, found an intermittent connection where I had connectorized the thermistor wires near the hot end. First clue was that temperature was reading as 3 C before becoming "DEF" on the head unit. Second clue was jiggling wires to make it work and break based on configuration.

Rebuilding to test. Hope I nailed it this time.

[EDIT2]

Well, I de-connectorized the Hot End Thermistor (cut out connectors, direct solder-spliced the lines) and things WERE looking good, but when I was jostling the lines, the Hot End read out at 6 or 7 C (way low) and both temps read "DEF".

When it does work long enough to heat up the hot end the thermistor is reading out ~160 C, but it must be WAY hotter due to the viscosity of the plastic that I can push through the nozzle.

Brand new thermistor in a brand new E3Dv6; same issue before and after the hot end swap. Do I need a RAMBO swap? I'm running out of things to change.

Help.