Bed Thermal Runaway  

RE: Bed Thermal Runaway

@merrill-a

nice that it works now 👍 

Finding out the reason why a reflash was necessary is very difficult to evaluate and hard to understand (at least for me). I would probably test the first board and not waste it too soon.

happy printing!

RE: Bed Thermal Runaway

Interesting that it happened after a new firmware update last year and has now happened again after another FW update built on the last ones. Too bad I did not keep information as to which FW update was installed when this first appeared.

Having worked in writing code back in the Dark Ages, you are right...finding the problem, if that is where it is, can be a huge task. Sometimes unrelated code causes problems elsewhere in the functioning of the software/firmware. Tricky even for the experts. Just look at Microsoft an the problems they have had and the ones Prusa has had with some of the MS latest updates.

RE: Bed Thermal Runaway

I have sent the problem to GITHUB under ticket #2898. Referred them to this Forum post but sent them most of the information held here. Not whole dialogue

I appreciate all the help.

RE: Bed Thermal Runaway

Well it is back again. Same problem. I did a reflash and it did not clear this time. Just a note that I had been using my MK3S exclusively since the last failure of the MK 2.5S, except for my successful print after the last failure and the reflash. Today I needed 2 printers so went and fired up the 2.5S and after a layer of printing it failed with the same Bed thermal failure error.

RE: Bed Thermal Runaway

@carl-a-2

What about the printer environment? Is the room cold, below 16 degrees C.?

RE: Bed Thermal Runaway

Room temperature kept at about 25 to 27 C. No fans blowing on it. During the first two failures it was in an enclosure (that my MK 3s is in now). No direct sunlight, humidity about 40%

Thanks Karl for your help before and your quick response this time.

RE: Bed Thermal Runaway

@carl-a-2

the ticket number (2898) you gave us is about another problem. could you upload a link?

RE: Bed Thermal Runaway

Karl, the ticker # is for Ultimchine I believe but will check.

RE: Bed Thermal Runaway

Now not sure about the ticket number but this Forum chain has all the information I gave them and GitHub. Here is a copy of what I just sent Ultimachine and they said they would pass to their tech people for review. 

The chain of recent events and readings in this post start on Nov 6.

"

Merrill Albury

[email protected]

A little over a month ago I contacted you about a Hotbed Thermal runaway error problem with my Prusa Mk2.5s. 
It has a mini-Rambo 1.3a mainboard. This is the second time I have had this problem. After exhaustive testing the 
first time, about a year ago now, I replaced the mini-Rambo with a new board. The first board had been running for 
over 2 years without any problem. When the new board failed, about 6 months ago, I sent you a message as to the 
problem; notified Github since I thought it might be a software glitch; and had extensive communications on 
PrusaPrinters.org Forum. This resulted more of the same tests (electrical and ohm readings of the board and the bed). 
Then someone suggested that I reflash the FW, which I did, and the printer tested OK. I did one fairly long print and 
had no problem. Since then I have been using my MK3S for all of my printing so did not get back to the Mk2.5s until 
today as I needed two printers for a job. After a little over 1 layer of printing I again got the bed thermal 
runaway error. I then tried a FW reflash but with no success. Since I find it hard to believe two boards would fail
 in the same way, I am looking for any ideas as to what the problem could be. I still have most of my notes from 
the last failure and also have the original board the "failed". I can add that the bed and thersister both read OK 
and a heat test of the thermsister (using a hair dryer on the bed) seem to rule out the bed as a problem.
Readings of the power supply likewise appear to be OK. Same goes for all wiring and wiring connections.
As I said the last time this happened, I am willing to ship either failed board back to the factory for 
testing if necessary.
You may find one of my emails under [email protected]"

RE: Bed Thermal Runaway

Can I assume that no ferther options are being offered that I will have to order and install a new mini-Rambo and maybe even a new heat bed?

I wish I felt confident that this would solve the problem. have not heard anything back from Ultrimachine after multiple emails. Any idea how I can get a response from them about the problem?

RE: Bed Thermal Runaway - solved again

Well all but for the loss of a horseshoe nail.....

Ordered a new mini-Rambo board, 12V MK52 magnetic bed, and a new PSU. So I now have most of the parts for another MK2.5S. Why, you ask?

Finally found, after orderings all the parts except the PSU, that one lead did not power up the mini-Rambo. Unfortunately I had been measuring on the retainer screws on the connector at the board and seeing 12V but after switching the PSU leads between the bed and power supply connectors, the problem moved. So I thought that one leg of the PSU was bad.

So I ordered a new PSU which PRUSA sent immediately as with the magnetic bed.

I should have known better as I had initially seen some white "stuff" around the negative DC pin on the Rambo which should have told me that there was corrosion on that pin and in the connector. DAH!

When I got the new PSU I hooked it up to the printer and all was fine. No more prolem.

Well as  final test before taking the whole printer apart and replacing all the "stuff" I had ordered, I tried each cable on all the DC supply screws on the PSU and plug on the RAMBO.  One cable worked fine but the other did not. So I again looked at the connector on that cable and, although I did not see any obvious corrosion, I used a 1mm hex tool to clean out the connector hole. Note that I had tried to remove and replace the connector but could not break the retaining screws loose.

After some back and forth testing, the printer worked fine. Don't know why there was corrosion on the ground pin of the RAMBO but when I find a new PSU to Rambo cable, I will replace that one and keep an eye on the Rambo pin in future maintenance vhecks.

If anyone knows where that PSU to RAMBO cable assemble can be obtained, please let me know. And yes I know I can use the one that came with the new PSU but unless I can remove the connector, it is difficult to remove the cable (assembled) from the PSU through the hole in the lower case. I have the printer working now so can wait for a new cable or build one myself from available assets in my shop.

Thanks to all for the help provided and all the troubleshooting, including from PRUSA help desk. Sometimes it is the simplist things that turn out to be the problem.

RE: Bed Thermal Runaway

Yep, spoke too soon. The initial tests went ok. Started a print today and after about 15 minutes got the same Bed Thermal Runaway error again.

It is looking like there may be a capacitor that discharges over time and then, when used for a few minutes and recharges or arcs, it fails again.

I will now replace the mini-Rambo and hope that there is not a problem with the heated bed.

Will update after a longer testing period.

RE: Bed Thermal Runaway

Well, I just could not accept that the PSU went bad so I went back to the connector (Molex) on the PSU power leads. I had replaced one but looked at the second on and, as with the first, it was brittle and the positive lead showed blackening. So I replaced it as well. Hooked it up to the printer and it worked fine for a 5 hour print. Left the new PSU hooked up but now have the following back-ups:

2 mini-Rambos, 1 PSU, 1 heated bed plate.

With all that, I may just build another Mk 2.5S (Bear)

I will also make replacing the Molex connectors a part of my maintenance check (if necessary after inspection).

This may have been the result of my multiple removal/reconnection I did due to upgrades and problem solving.

RE: Bed Thermal Runaway

@carl-a-2

An extra controller board is not a bad thing to have.  I have one I am replacing because ti has a bad language chip and SD card on the display.  I will use the ones I remove as back up.  

RE:

Thanks a lot for your update, Carl! I had the exactly same issue and would have ordered a new board if you had not written about your molex connectors. Mine was a bot molten. Changing it fixed my heat bed.