Solved Bed Heat Inconsistent

For the last few days, my bed temperature is very inconsistent. Usually it won't heat beyond 32 degrees and sometimes not at all. I have checked the voltage at the Arduino board and on the leads going to the bed heater. Both are a solid 12 volts (so I know it's not the fuses). I have also checked the continuity of the bed heater, it reads a solid 1 ohm. No amount of juggling the leads makes any difference. When I manually issue a heat bed command, I never get a response - It just waits forever.

I am at my wits end and just about to pull the trigger on an order for a different printer - one that isn't a science project.

 

Could be that the thermistor is loose against the bed and not making contact to measure the temperature. Does the temperature reported relate to a "feel test"? or preferably an IR thermometer

 

I had a similar problem with the heat bed last week. Sometimes it would heat and sometimes it wouldn't heat at all. My problem was in the grey cord that has all the wires in it beneath the print bed. Where it was bent 90 degrees next to where it was glued down, the wires inside were broken and would short out sometimes. Carefully splicing them back together with a soldering iron and heat shrink tubing fixed the issue.

 

Yes, Mike. The bed is barely warm and my IR thermometer agrees with the display in MC. Bad thermistor or loose one is a possibility, but after removing the bed, I couldn't see a problem. An ohmmeter check of the thermistor leads did show a half-scale reading on the 100,000 ohm range, so I know it's not completely dead or open.

It's been days since I had a decent print (can't get the PLA to stick to a lukewarm bed, no matter what). I am tired of all the fiddling around.

 

I'm a bit stumped. It sounds to me like a loose connection somewhere. Though the ramps board may have gotten damaged if it refuses to heat at all. Look underneeth and see if an LED turns on when you enable the heated bed.

If not I'd give robo a call on the 24/7 support line: http://www.robo3d.com/pages/schedule-robo3d-printer-tech

 

I checked again this morning and can give a few more details.
When I heat the bed, the IR thermometer rises to about 51 degrees, but the MC temp display shows rising to 40 something degrees. Then after a minute or two, both temps drop back to around 32 degrees, stay there for a few minutes and then drop again to temps in the 20s. I haven't yet carefully watched the LEDs, but last night I noticed one LED start out green then I remember seeing a red LED and at one time one LED was flashing red.

The problem I was originally trying to solve was lack of sticking to the bed. The skirt seems OK, but as the support structure is laid down, it is MUCH thinner and refuses to stick. Soon I have a globbed mess.

 

Problem solved. It was the fuses. The fan was not running at full speed, so the fuses got hot and tripped the bed heater. When the fuses cooled, the bed heated up again. This cycle repeated but never enough to reach desired temperature.