Bed won't heat...

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dsharp02
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Joined: Tue Jun 30, 2015 2:52 am

Bed won't heat...

Post by dsharp02 » Mon Sep 03, 2018 3:36 am

I was in the middle of a print when all of a sudden I noticed that my bed temps had started dropping. After the print was complete, nothing I did could get the bed to start heating again.

Measuring the voltage across the bed power pins, I get 12v. However as soon as I apply a load, the voltage drops. With a 10K-ohm load, the voltage dropped all the way down to 1v.

Is this a bad/blown mosfet? This is an old M2 (August 2012 vintage) and pre-dates the 24-volt conversion. The board still has the yellow PTC rather than the automotive style fuses.

How much would an upgraded RAMBO board cost?

How much for a 24v conversion kit? Does MG still sell the conversion kits? I was told there was a change to the wiring harness that would have to be made when I first inquired about this 4 years ago.

Does MG offer trade-in credit towards the M3-ID? :D

Thanks,
Dave

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ednisley
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Re: Bed won't heat...

Post by ednisley » Mon Sep 03, 2018 6:01 pm

dsharp02 wrote:
Mon Sep 03, 2018 3:36 am
Measuring the voltage across the bed power pins, I get 12v
With a 12 V heater, the most likely problem is at the power input connector on the RAMBo board. The wires from the 12 V power brick generally work loose inside their screw terminals, whereupon the absurdly high current heats up the weak joint and destroys the connector. You can find some hideous pictures somewhere on the forum.

Next most likely is a broken wire between the RAMBo and the heater, caused by repetitive stress injury from all that back-and-forth motion. You may be able to find this with a ohmmeter and some wiggle-jiggle action on the cable, but if even one strand remains intact, the resistance will remain very low at the meter's trivial test current. Pulling the wires out of the braided sheath will be more definitive; the insulation will be wrecked at the break.

Least likely seems to be the connector where the cable from the heater terminates on the RAMBo.

Start by inspecting the connectors; you may find some seriously charred plastic.

Depending on what you find, you may have a zero-dollar repair.

dsharp02
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Re: Bed won't heat...

Post by dsharp02 » Thu Sep 06, 2018 3:35 am

It's like you're psychic.

Image
Link to the photo that for some reason won't post: https://photos.app.goo.gl/1y162QSmAZoDvBmo7

Dave

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ednisley
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Re: Bed won't heat...

Post by ednisley » Fri Sep 07, 2018 2:37 pm

dsharp02 wrote:
Thu Sep 06, 2018 3:35 am
It's like you're psychic
Suffice it to say you're not the first person to see charred plastic … [grin]

dsharp02
Posts: 23
Joined: Tue Jun 30, 2015 2:52 am

Re: Bed won't heat...

Post by dsharp02 » Sat Sep 15, 2018 4:34 am

So I'm working wiring up the 24v power supply and v3b->v4 extruder upgrade, and I get to the point where I'm supposed to use the 4x M2-18 bolts to connect the mounting plate to the belt clamp. Unfortunately, the nuts in the clamp seem to be M2.5, so my bolts are too small. Should I have received 4x M2.5-18 bolts in my 24v upgrade kit? I didn't see any.

Edit:

I solved the missing M2.5-18mm screw problem by just using the M3 screws from the old plastic block on the back of the original M2 extruder plate. However I'm now having problems attaching the 24v fans to the new v4 filament drive. The instructions say that I should use a M3-45mm, but my M3 is only 40mm. It's a bit frustrating that the upgrade kit didn't come with all of the necessary screws. Those of us with really old M2s may not have the ones that the kit is assuming that we can re-use. Plus none of the local hardware stores seem to carry M3 socket cap screws in the lengths I need.

Edit:

There wasn't an M3-45 in the kit, but there was an M3-50mm included that I couldn't find any other use for, so I just used a few washers to tighten things up. (The white spacer from the original fan mount was too large). The only issues I can find at the moment seems to be that the z-endstop triggering seems to reset the entire board to where octopi loses the ability to control the printer and I have to disconnect and re-connect to get things working again.

Edit:

Well I thought the z-stop was the only issue, but apparently my motor mount needs replacement. I'm trying to print one on my mosaic, but the bed is taking forever to get up to 100C. Anyone know if there is a safety problems with running the Mosaic heatbed at 24v instead of 19v?

Thanks,
Dave
Last edited by dsharp02 on Mon Sep 17, 2018 2:51 am, edited 1 time in total.

airscapes
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Re: Bed won't heat...

Post by airscapes » Sat Sep 15, 2018 3:35 pm

The lack of metric hardware in the US sucks! I am dealing with it right now trying to source what I need LOCALLY to build a prosthetic arm for a child. All though school "we" were taught the metric system and it was cake, no freaking fraction to deal with!! But NO, the old farts that run the USA refused to follow the rest of the world... Give MG support a call, I am sure they will send you what you need.

dsharp02
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Re: Bed won't heat...

Post by dsharp02 » Tue Sep 18, 2018 2:51 am

Ok, so after printing a replacement motor mount on my Mosaic, I was able to get everything physically installed, however I still have a problem, and I think it has to do with my machine home toward z-min rather than z-max. As soon as my z endstop triggers, the firmware resets.

Looking at the terminal I see the following:

Send: G28 Z0Recv: \x00��\x00\x00start
Recv: echo:Marlin1.0.2
Recv: echo: Last Updated: Aug 27 2018 11:07:16 | Author: (MG|Josh, M2E - (SnNRd) v100 02/18/2016)
Recv: Compiled: Aug 27 2018
Recv: echo: Free Memory: 3259 PlannerBufferBytes: 1232
Recv: echo:Hardcoded Default Settings Loaded
Recv: echo:Steps per unit:
Recv: echo: M92 X88.88 Y88.88 Z1007.70 E471.50

At this point, I have to disconnect and then reconnect to re-establish control of the printer. Is there a github repo with a Firmware that will work on my (very early) M2?

Thanks,
Dave

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ednisley
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Re: Bed won't heat...

Post by ednisley » Tue Sep 18, 2018 2:40 pm

dsharp02 wrote:
Tue Sep 18, 2018 2:51 am
As soon as my z endstop triggers, the firmware resets.
The Z endstop cable is plugged backwards into the RAMBo socket.

The RAMBo socket has three pins: [+ - S].

The two-wire switch cable ends in a three pin connector shell (*) with one empty contact. Unfortunately, the cable connector is not symmetric, not keyed to fit the socket latch, and easily fits into the RAMBo socket either way.

Plugged correctly, the two switch wires go to the [- S] socket pins, putting the [+] socket pin in the empty contact.

If the cable is plugged backwards, the two switch wires go to the [+ -] pins, putting the [S] pin in the empty contact.

Plugged backwards, when the switch trips, it shorts the power supply to ground. Unpleasant consequences ensue.

(*) I'd be unsurprised to discover a machine with a two-wire switch cable ending in a two-pin connector shell. Those must plug into the [- S] pins, leaving the [+] pin waving in the breeze.

dsharp02
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Joined: Tue Jun 30, 2015 2:52 am

Re: Bed won't heat...

Post by dsharp02 » Tue Sep 18, 2018 11:02 pm

My printer is now back up and running, but with the firmware on the Rambo, I had to home my Z-Axis in a funny way.

Basically I have to issue M18 to turn off the motors,
G4 P6000 to wait long enough for the z-axis to finish dropping to the bottom,
G92 Z207 to set the current z-position to 207mm.

After that I can use it normally. Can stock Marlin be used on the M2? I seem to recall years ago that there were things in the M2 firmware that weren't in Marlin (electronically setting current limits?) Will this be an issue? Or is the Rambo board old enough now that full support is now in the baseline Marlin firmware?

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