Solved Bed heater no longer heating (second ramps board)

Hey guys,

Been a long time Robo R1 + user since 2017. I haven’t had many issues and the ones I have had I’ve been able to solve reading this forum. About 1 month ago replaced my bed with a new stock bed I bought a year or two ago. I started having issues with the heater bed. It just stopped working altogether. I tested the voltage coming in from the power supply and I was getting 12V at the 11Amp terminals. I wasn't getting anything at the D8 terminals (no bed heater led either). I was getting ambient temperature from the bed thermistor. There aren't any issues with the hot end. So. I don’t think it’s the power supply which I replaced a month ago.

I swapped out the stock board for a generic ramps 1.4 board. I thought about swapping out the Q3 mosfet, but decided on the generic ramps 1.4 replacement instead —same price for 5 mosfets as for the board itself. I swapped in the new board and everything was working fine. So I started an ABS print and set the bed to 80 degrees Celsius, The print ran for 4 hours and then the bed temperature just dropped out. I checked the board and found the dreaded melted power supply connector at the 11 amp terminals.

About a week or so ago, I was experimenting around and configured marlin 2.0.9.3 for the printer. Everything appears to be working great. I can’t see any reason this could cause the issue, unless there is something I completely missed.

One of the reasons for updating the firmware was to to set up mesh bed leveling (which has dramatically improved my print quality) and filament runout with optical for jamming, as well as to temperature runaway protection.

I ordered an external mosfet to take the load off the ramps board. I should be getting that some time today. I think that should solve my problem, but I'm concerned something more is going on here.

What should the resistance of the heater element on the bed be? I'm getting 1.5 ohms.

Do you have any idea what can be causing this?

I’ll update after the mosfet is replaced.

Thanks for the help
Stratocasertr

 

I installed the external mosfet and replaced the melted connector and all seems to be fine right now. Ran a few prints with out issue. The external mosfet doesn't even get warm. I was curious about what was causing the metling connector since it happened on two boards. Any I guess I can consider this solved.

strat

 

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Thanks for the reply. Strange that it just started happening. I was worried there was something I missed in the configuration, since it happened on two boards. For me the only solution is the external mosfet. Just ran an ABS print with bed heater at 110 without issue.

Thanks
Strat