Voltage drop on D9/D10, Ramps 1.4

Hi all,

I try to get my chinese i3 up and running, but I have a problem with heating up the hotend.

When I heat up the hotend, after around 10 seconds, there is a warning "Heating Failed" in Pronterface. The hotend does not get hot at all.

Setting hotend temperature to 230.000000 degrees Celsius.
Error:Heating failed, system stopped! Heater_ID: 0

So I measured the voltage on D10, and I only get 0.1V. However, if I disconnect the Hotend and start heating, Voltage at D10 is 5V. As soon as the hotend is connected again, voltage drops to 0.1V. Same behaviour on D9

If I take an ATX PowerSupply and connect the Hotend directly to 5V there, it heats up nicely.

The heated bed on D8 works perfect, so do all the steppers etc. The temperature reading of the Hotend is also correct

PowerSupply is a 12V 33A, Ramps is 1.4

Any idea what could be wrong?

The hotend takes 12V not 5V.
Did you connect both power-inputs to 12V as it is supposed to be?
Also the 5v regulator on the Mega board is quite weak. Sometimes the voltage is to low to switch the MOSFETs fully ON, which leads to excessive heat in the FETs.
( That's more a problem with the 11A bed circuit than hotend )
-Olaf

Quote
o_lampe
The hotend takes 12V not 5V.
Did you connect both power-inputs to 12V as it is supposed to be?
Also the 5v regulator on the Mega board is quite weak. Sometimes the voltage is to low to switch the MOSFETs fully ON, which leads to excessive heat in the FETs.
( That's more a problem with the 11A bed circuit than hotend )
-Olaf

Or could it be as simple as the board had 7805 voltage regulators fitted instead of the Mosfets (wouldn't be the first time that has happened with Chinese clones) that would explain the 5V on the D10 connector dropping to practicaly 0V when effectively shorted by the heater?

Doug

Thanks for the inputs, but so far no success.

Quote
o_lampe
Did you connect both power-inputs to 12V as it is supposed to be?

Yes. Just verified them again, both have 12V on the connector, and also on the board (just to rule out a broken connector)

Quote
dougal1957
Or could it be as simple as the board had 7805 voltage regulators fitted instead of the Mosfets

All three are P55NF Mosfets

Also tried different USB-Ports for the Mega.

When I switch on the hotend, I can hear the fan in the powersupply to turn faster - so it takes more power somehow...

Probably a shorted hotend heat element?
Unscrew one wire of the hotend end measure resistance of the heating element.
-Olaf

Solved!

The (presoldered) Ramps-Board had Pins 9 and 10 shorted. I resoldered them, now everything works fine!

Thanks for the help anyways