Bed heater stopped working

dandan

Hi,

after an overnight print I tried to start another one and realized that the bed isn't heating anymore. For what it's worth: Last prints were PETG, so around 75°C bed temperature as opposed to my usual lower PLA temperatures.

Any ideas on where to start troubleshooting?

Samuel Pinches

Hi @dandan ,

Have you checked the dedicated A5 FAQ page on the wiki (see the stickied post in this category? There is a section regarding exactly how to troubleshoot heating issues in there. Happy to answer any specific questions.

Kind regards,

Sam

dandan

Hi Sam,

thanks, I did check it but unfortunately it doesn't solve my problem.

My model is a newer one without the drag chain and the cable is fine and everything is plugged in. Also the sensor seems to be fine as it reads the ambient temperature and not -15 or something like that. Don't know where to go from here.

Samuel Pinches

Ok, so it's reading the temperature fine, but it is not heating.

So one of these must be true,

• A ) There is a fault with the bed heater itself
• B ) There is a fault with the heater wires to the bed
• C ) There or a fault with the mosfet on the board

I would suggest, swap the thermistor connections for the nozzle and the bed, and swap the power connections for the heaters of the bed and the nozzle. Then try heating the "bed" (which should cause the nozzle to heat), and see if the "bed" (nozzle) temperature increases. That would confirm the bed mosfet is working. If not, then that confirms the bed mosfet is blown.

If that is the case, then the easiest option is to replace the main motherboard, which is not that expensive. There is no spare mosfet on the motherboard that is adquately rated for use with the high bed currents long term.

dandan

Swapping the power connections would be to unscrew and swap D10 and D8 in my case according to this diagram: 

Thermistors would be A15 and A14 on the bottom right of the diagram?

Just making sure I understand correctly before I do it.

Samuel Pinches

Yes, that's the way

The thermistor is actually A14 and A13, because the labels are not aligned with the plugs, but yes, you have the right idea.

Werewolf

First of all just check a connector of heating bed and power cable. Usually on A5 models due to overheating the contact miss on +24V or GND circuits. At least i have met a same problem month ago, and a had to replace a connector.

Der_Muck

If we wanna get save and professional, we rather go better with a drag chain cable.
As I am not an electrician I must find out the wire diameters and than find a cable what is not so stiff.
It would be a realy save and professional solution for us all because a cable break can always cause a failed print or even a fire or minimum total smoked home. 

Samuel Pinches

The original A5 (nov 2017 - march 2018 approx.) came with a drag chain which was really good. But the cables were too flexible, so the bending motion only occured at one point in the chain, causing a local fatigue failure.

So actually, you need a cable that is stiff enough so that the cable motion is smooth. The cable should not be too big, or too thin. It should not be too stiff, or too flexible. It really requires a proper engineer and proper testing to ensure the solution will last a long time.

JGAurora decided to take the easy option, and instead of fixing the problem, they just removed the cable chain all together, which is a real shame.

Der_Muck

Yeah but a drag chain with the wrong cable is the dead of the cable because it flexes always in the same direction and cause a quicker break than a cable what is free in motion and can bend in a free room. The bends are less drastic than in a drag chain. So JG took the chinese solution to be 1. cheap 2. it does the job well and 3. got the breaking cable problem solved so its good work for all but no professional solution but again its cheap.
Drag chain cables are made for a drag chain but I dont know a cable what isnt to stiff for the JGs print bed.

I have a 3 wire diam. 2,5mm shielded dragchain cable here, it is 1cm in diameter and muuuch to stiff for a quick motion of the JGs bed. There must be 6 wire cables in it. So maybe there is a flat 6 wire dragchain cable available. That would be better. At 30A 24V they say it would be a 8mm² cable, so for the JG it would be 4mm²  that would be norm savety.

Samuel Pinches

I have been suggesting to people with the original drag chain, to keep the flexible wires, and add some PTFE tubing or thick nylon cable ties inside the cable run as reinforcement. That should prevent the repeated kinking of the chain in the same spot each time.

Der_Muck

That can help yes but has to be to the connection otherwise when it ends to early you get again a sharp bending area.
The cables would break there.

As I look in my drag chain free JG the cable barely moves cause there is a loop of the wire.

Samuel Pinches

It doesn't move much for small prints, but I think for regular large prints, the drag chain might be more valuable?

Der_Muck

I realy cant tell you, that can only those say that have that drag chain, I can only guess about it.
For me it doesnt look bad without the drag chain. But I will search for a usable drag chain with propper cable for it.

cs2000

 I just had this same issue, but it was a different outcome. I came back to the LCD screen saying the system had been halted due to a fault with the bed heater. OK, weird.... Hang on, whats this black dust underneath the print bed.....

So I take off the print bed to find a missing Thermistor...seems I set my bed height just a tad too low seeing as its now a pile of dust, id basically sanded it off as the bed moved too and fro and its now just thermistor dust on the top of the printers base   . Off to ALiExpress for a new print bed heated surface....

Samuel Pinches

Oh no @cs2000 Doh!

Der_Muck

Oh maaann thats bad to hear  

cs2000

On the posotive side, id rather a new bed than a melted bed connector or a blown MOSFET on the motherboard, at least that easy to replace!

Guess il have to set my bed height a touch higher next time! Doesnt help that the metal frame is rough, its literally sandpaper, plus i had the bed at 105c as was trying to print ABS, it probably made it expand/sag a little more than the 55c i print PLA at !

Annoying as its delayed me getting my IR bed sensor working (i was printing the mounting bracket at the time). I know the sensor isnt supposed to work well on the black diamond build plate, but im going to flip that upside down anyway as im switch to PrintBite. Printbite is IR transparent, but i can trigger the IR sensor from the plain glass surface underneath it and just modify the Z height offset to get around that issue.

Der_Muck

You want to level on the glass with the IR probe? That doesnt work.

cs2000

Sorry, was being a little brief. Im going to paint the underside of the printbite, or the top of the glass, or do something similar so give the IR a good surface to measure from, just like its written about on the guide on the wiki.

I think the glass bed is actually needed, otherwise id have just binned it. From playing with the bed levelling screws, without the glass plate, I found the bed warps pretty easily without the glass there as a brace to support its overall shape.

Il have a sandwich of

Heated Bed > Glass Buildplate > IR reflective material/paint  > Printbite

From my brief materials testing of stuff I have laying around, even regular printer paper printed totally black with a laser printer blocks IR light, so il probably be using this, at least until I find it doesn't work. Paper should be "safe" too, it wont self ignite until over 230c, and if your bed is at that temperature, you have other problems seeing as regular 60/40 tin/lead solder melts at 188c and even this lead free rubbish melts at 217c. You'd have the bed connector and thermistor falling off of your heated before the paper caught fire.

Failing that, Kapton tape has a very good IR emissivity, so a wide roll or if available a sheet of that, applied to the (now inverted) glad bed would also work very well.

For what its worth, the guy who actually designed and builds the specific IR modules we're buying says from the get-go, they're designed to work on glass, so seems like info all over the web is confused.

https://reprap.org/forum/read.php?94,519697

Der_Muck

I also had a IR probe on my printer but it failed badly. It was the accuracy that was so terrible on the black diamond plate that I change to the BLtouch. The accuracy is better than it was with the IR probe.
I dont thing a IR probe would be accurate on a glas ever. Even one hair can get the probe to a wrong measurement, also the heat can do that.  
My goal was to be 0,03mm accurate but it was not passible at all.

I print with kapton its very good to print on it yes. 
But still, I dont think a IR probe would ever can work propperly on a reflecting or griddy surface.