Heated bed not getting power to D8 output.

Hi, I recently finished my mendel90 and was too lazy to setup the heated bed until recently. I finally got it all going however when I send the command to heat it there is no 12v going to the D8 output. The heated bed thermistor is giving a correct reading, the heater itself is measuring proper resistance, just no 12v. I suspect some pin assignment issues, no idea how I would fix that in Marlin. I also checked for bad soldering points but it all looks good. Fuses are not the problem because the heater has never been used yet. Open to any suggestions thanks.

Are you connecting power to both inputs on the RAMPS? The 11 Amp connector feeds the bed. The 5 Amp connector feeds everything else.

I'm having the same problem and it turns out that the 11A fuse is flakey.

However, the RAMPs controller controls the temp by turning off and on the Negative side. 12V is powered full time.

As I inspected the solder joint, and I was not pleased the size the board traces from the 12V lead to fuse. I soldered in some extra wire to to eliminate the trace as some of the problem.

Mike

Measure the voltage between D8's + terminal (should be next to the power input connectors) and the power supply's ground. If you have 12V, then your fuse is likely fine and you have a problem with your MOSFET or the pin that's controlling the MOSFET. You should have 12v regardless if the heater is being called for. If you don't have 12V, then check directly at the input terminals. If you have 12V there, then your polyfuse is not working. Replace with automotive style blade fuse or another polyfuse (they aren't expensive either way)

With everything off, measure resistance between the D8 - and the MOSFET's center pin. The D8 MOSFET is the one oriented differently than the other two. It should mesaure nearly 0 ohms (shorted). Measure between the top pin of the MOSFET to power input - next to D8. It too should measure nearly 0 ohms. If both of these are near 0, then your ground traces should be good (but not necessarily the mosfet. If they measure open, then you have a broken trace or a bad solder joint. Both fixable.

Still with everything off, measure between the bottom pin on the MOSFET and pin d8 (6th pin from left on top of card). Resistance should be around 10 ohms I believe. As long as it doesn't read open, it should be good and the trace from D8 pin to the MOSFET is good. If it measures open, then it could be a bad resistor, cut trace, or cold solder joint. Possibly easily or more difficult to fix..but definitely fixable.

Finally, with the printer on and calling for the bed to heat, measure for voltage between the bottom pin and ground. If it measures ~5v, your pin is properly configured and trying to get the MOSFET to work. Replace the mosfet with a compatible one. Search the forms for the correct type. IRL something something something IIRC.

Tried first suggestion on making sure I have a connection to the 11a power input because apparently that controls the heated bed. Checked power supply for 12v and powered up. Arduino immediately started smoking, arduino is definitely dead so a new one is on the way. How should I test the RAMPS to make sure nothing blew up on it. Visually it looks fine but just want to make sure. Also how can I avoid my arduino from smoking in the future.

Did you have the 11A power polarity correct? - the outermost terminal is negative.

---

_______________________________________
Waitaki 3D Printer