Hotend and bed not heating

I am building an i3 clone with an e3d v6 hotend and a heated bed, and have loaded the marlin software to my Ramps 1.4

However, Pronterface is not registering any temperature for either the hotend or the bed, and when I try to set the hotend and bed temps I get an error saying that Mintemp has not been reached and it wont heat either.

How do I tell if the thermistor's are working? It seems unlikely that both thermistors are broken.

Also, what voltages should be showing at D8, D9 and D10? I'm not seeing any voltages at either which doesn't seem right?

Thanks.

You cant turn on the heaters if it can't read a sane room temperature. Its a "safety" feature

So you need to get your temperatures reading correctly.

Thermistors are just resistors that change their value with temperature. Unplug it from the controller and stick a multi meter on the thermistor cable, it should read about 100k at 25c

re voltages. D8, D9 and D10 both pins should be 12v with respect to gnd. The -ve pin will drop to gnd when its active to allow current to flow.

Thanks for the reply Dust,

I assume you mean 100k Ohms for the thermistor (I am still learning about circuits/electronics).

So, if not reading any voltage at D8, D9 & D10 I also assume that means I have a faulty Ramps board, or could it be that voltage is only applied when the relevant command is given? In other words, could it be showing no voltage at because the thermistor is registering zero temp and therefore not sending a command to heat the bed/extruder?

D8 + get 12v directly from the 11amp 12v plug (after the fuse)
D9 + and D10 + gets its power directly from the 5amp 12v plug (after the fuse)

These are on always, as long as the power is on.
Something seriously wrong if you don't get those...

Make sure you are using a real gnd for you multimeter (eg either -ve on the power plugs) ... as for eg if you measure voltage from D8+ to D8- both being at 12v, will read 0v

Do you have yellow square things (poly fuses) or real fuses just behind the green power sockets of the ramps?

Have you wired up the ramps power? both the 11A and the 5A plugs.?
Did you turn the external power supply on? (have to check!)

Edited 1 time(s). Last edit at 08/02/2017 05:30AM by Dust.

I was measuring directly from the D8 +ve and -ve terminals, but when I measure from power ground I get the 12v as you suggested, so that's not the problem.

The board I'm using has the yellow poly fuses, and I have power going to both the 11A & 5A plugs (I assume you are talking about the green power socket), which are both showing 12v.

However, I'm not sure if I'm measuring properly, but when I measured the bed and extruder thermistors I got zero resistance on both. Is there a trick to measuring them properly?

Depends on the meter, if its digital, as long as you set it to ohms, most auto range.

But it could be a old meter... in which case may to have to set it to a range that is larger than expected value.

eg looking for 100K ohms, set to 200K range

It is a pretty new meter and does autorange, and the reading I get is 0L, which I thought was a zero reading?

no OL is overload, to high to read

[learn.sparkfun.com]

so does that mean that the thermistor's are faulty?

Are you measuring the resistance with the thermistor disconnected,(hopefully)

What meter are you using ?

Hi obewan,

I am using a Digitech QM1321 multimeter (photo attached) and measuring the thermistor disconnected from the board. The attached photo shows how I have been measuring it and the reading I am getting. The one being measured in the photo is the one stuck to the bed, however the one attached to the hotend is showing the same reading and both components came from different suppliers.