Debugging intermittent heat bed fallout

Hi,

My heat bed was working fine on a Ramps 1.4, but sometimes it would stop heating, but come on again after some days.
Now it is completely gone. (MendelMax 1.5)

I have tried replacing the large polyfuse with a 15A carfuse.

When the heat bed is disconnected, the LED turn on/off when I set the temperature from pronterface (with a 2 sec delay, (the nozzle LED turn on/off ímmediately)).

When the heat bed is connected, the LED does not turn on.

The resistance of the disconnected heat bed is 1.5 Ohm.


Is replacing the Mosfet my next move ? (it already has a small heatsink and cooling fan).


Thank you,

That would be my next step, before you do that though I would check the power output just to be certain it is getting enough.

So, I tried replacing the Mosfet closest to the D8 connectors with the heat sink.

Same as before,...

With no load the LED turns on, and there is 2.4V on D8.

When I put a load on D8, heat bed or fan, the voltage is 1.2V and the LED does not turn on. (I'm guessing the output voltage is also driving the LED?)

When the bed is turned off there is +-0.2V on D8.

Any thoughts ?

Thank you.

Oh, and there is 12V on both main inputs, also when there is load on D8.

Could it be a software issue, although I have not changed anything.

Thank you,

Before I buy a new shield for the Arduino, is there something I should measure first ?

-or is there a better subforum to ask in ?

Thank you,

I realize I am mostly talking to my self here, but in case anyone stumbles upon this thread in the future.

I replaced the shield, but as I did I noticed one of the 12V connectors was melted and corroded, so this was probably the cause.