Heated Bed Died on me.

Hi Guys,

I have beeing running a Mendel i2 with Ramps 1.4 and a 16A 12V PSU for some time now.

Some time ago the Bed stopped working, I came to the Frum and read about adding a FAN for the MOSFET, did that and the Heated bed came back to life.

Yesterday, after somo 12 hours of printing the Bed simply stopped working.

I have tryied (with no luck):

1) Removing all power and switched ev. back on
2) Verified all conections and solder points.
3) Unplug the MK2 Heated bed and Plug a Brand new MK1
4) Tested the Resistor and it Reads 0.972 Omhs
5) Tested the Heat Bed and it Reads 1.1 Omhs (the MK2 which was running) MK1 Reads 1.5 Omhs
6) With temp set on PrintRun the E8 ports is sending 4 Volts. Ev. else was turned off.
7) Power supply provides 12.2 Volts at both ports (which connect to both ramps inputs)

Looking for Ideas / Suggestions.

Regards

Crispy
Quilcam
Buenos Aires - Argentina

Crispy,

it sounds like a bad MOSFET.

With the heated bed turned on can you measure the voltage at the gate? It should be 5V.

If there is 5V at the gate and there isn't 12V at D8 then you've probably got a bad MOSFET. Do you have a heatsink on it? If not replace the bad MOSFET and add a heatsink. Blowing a fan on the RAMPS board isn't a bad idea.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

Thanks for the tips akhlut .

I'll get to that tomorrow.

Do you know if there is a way to test the MOSFETs with a digital multimeter???

Thanks

Crispy

Crispy Wrote:
-------------------------------------------------------

>
> Do you know if there is a way to test the MOSFETs
> with a digital multimeter???

Yes, Akhlut told you exactly what to check.

Ok, Done that, and it looks like the MOSFET is dead.

Difficult to get the multimeter in there tough. It does have a heatsink and, yes I have a quite big cooler (PSU size) there. Looks like 30 hours of straight printing was too much...

Will replace and come back.

Thanks for all the info.

They're easy enough to replace. Just snip the leads off at the body of the MOSFET and desolder the pins individually - much easier. You may need some solder-wick to clean out the holes before getting the new FET in there.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]