Heated bed erratic behaviour

[Francisco]

So the heated bed on my Rostock Max v3 is not working as it should.
When I start the machine and choose 60 for the bed it starts warming up all right and once it gets to 60 it stays tehre for some time maybe ten minutes but then it goes off and the temperature starts to go down. So now the bed is not heating (the thermistor works though) and I restart the machine and it takes several restarts and some time until it starts heating again but with the same behaviour.
Any ideas?

[AlanKilian]

Are you using the controls to set the bed temp and not starting a print? Mine does that also. I think there's a timer that turns the bed heat off a certain time after no printing.

[Francisco]

Are you using the controls to set the bed temp and not starting a print? Mine does that also. I think there's a timer that turns the bed heat off a certain time after no printing.

This happens during a print and also when heating up without printing. I'll get a voltimeter and test the electricity to be sure where is the problem.

[ivanhandler]

I have the same problem and I can't ever get to 80 C. When I try, it stops around 78 and eventually I get a def notice on the lcd and need to reboot. Anyone have any idea what's happening? The temperature drop only happens after the first layer so I am less concerned about that. Also in my experience the temperature comes back after a few hours (if you are doing a long print).

[IMBoring25]

The 0.92 branch of the firmware has a feature called watchdog that monitors temperature commands and actual temperature. If a certain amount of time goes by with the heater running but no increase in measured temperature, it decides something has come disconnected and throws the def error.

If it is really doing this at 100% duty cycle it could be appropriate to check the voltage being delivered and make sure you're getting 12V under load. If it's not it might be a simple PID adjustment. In any event, check that all connections are clean and tight.

[ivanhandler]

I bought my Rostock pre-assembled, probably a mistake. Where do I check the voltage load? What is the PID and how do I adjust it? Thanks. Hopefully I will get these and other questions answered this weekend at MRRF.

[Francisco]

Well it appears that fastening the screws that hold the heated bed cables solved the issue.
(both to the conector in the rambo board and to the power suply)

[IMBoring25]

Glad you found it. It's not a bad practice to re-check those on occasion. Before the watchdog you might have joined the melted-terminals club.