heated bed quit. Board LED doesn't come on

My printer has been running flawlessly for a while now, but today the bed won't heat up. The red LED on the RAMPS (1.4) board doesn't come on when I click the bed-heat button in Pronterface, or if I manually send M190 S65 through the 'send' box in Pronterface.

Can someone here help me with how to troubleshoot this?

Thanks!

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You've probably blown the D8 mosfet or burned out one of the relevant traces. Or, its a wiring problem and the 11A terminals are no longer connected.

would that disable the red LED on the board? I would think that would come on regardless of status of the MOSFET

Look at the schematic. The LED is in parallel with the load, so it lights when the mosfet is on.

that would make sense, then. I hadn't seen the schematic. Now that I looked it up, I see what you're saying. I'll change out the MOSFET and see if that fixes my problem.

Thanks for your info!


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MOSFET wasn't the problem. one of the wires from the bed thermistor broke and the board was reading zero. Found it when I changed out Q3 and it worked...for a bit. Then quit again. no LED, no heat. I happened this time to notice the zero in pronterface in the B: reading and put my meter on the plug end; it read open. I traced it about 6 inches to a break inside the insulation. After I spliced it back all is well now.


Just FYI,

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