Unexpected heating from ramps 1.2 !?!

Okay, this has totally confused me and I'm at a loss for what to do really xD so unexpectantly, out of the blue my ramps has decided that even when it's been told to stop, it wants to put ~9.5v through my heater (my psu currently gives ~ 11.5v into the ramps atm) ,and the only way to stop it heating is to turn off the psu. I've check for any shorts or problems with the boards, but it hasn't been touuched since before I was having this problem, I was thinking that one of the transistors have gone, but that's just my guess. Hopefully not as I had to special order them as no one near me supplies or have even heard of them, (deep in the brummy region of Dudley) :/

Anyone had any experience with this before? Could anyone with a higher understanding of electronics than me (which would be most people), possibly know what to do?

I'm at a loss of what to do really

Cheers, Ollie

Bed heater or extruder heater?

I've had the mosfet controlling the heated bed fail twice (the mosfet gets dead hot and ends up gray & toasted - eventually burning away the track...)

It's strange, because it's well within the rated capacity for the mosfet - and after I had one fail the first time I stuck some decent heatsinks on.

My solution was to use a relay controlled by the mosfet to switch the heated bed. I had to do a bit of firmware hacking to stop it switching too often (sounded like a geiger counter originally - wouldn't have lasted long).

I got all the bits from [rapidonline.com] and still have a few spares kicking around in a box somewhere...

Cheers,

Doug

Hi Doug,

It's the extruder heater, I did a quick run over of the board, but it all looked fine, but I've never had one die on me so I don't know what to look for
Your hack sounds pretty interesting, I'd like to hear more

Ollie

I've fried a few MOSFETs on my bed, but in my exp, they generally fail open/closed.

If your seeing ~9.5 volts, its switching...

Okay, well with my "extensive" knowledge of electronics, I decided to swap the heater over to another adjacent MOSFET and reprogrammed the firmware accordingly, however the mintemp alarm keeps stopping my attempts to heat, I think this may have happened at the same time the mosfet blew >.> but it's still reading fine and my mintemp on the firmware is 0 Celsius so I'm not sure what I've buggered this time....

It may be helpful if I told you all that I was running Marlin, but I dunno, again xD but I've tried a separate thermistors had lyin round and that was reading fine like the first.

Whoop for my failings...

Ollie