Extrude Hotend AND Bed will not heat up

Hi All - I developed a problem with Hotend AND bed heaters on my Mendel. Its been perfect for months apart from the occasional Hotend heater resistor replacement. My first thought is a failed themistor but it looks intact. It might be a setting but not sure where to adjust it. The symtoms are a reading of 304c in pronterface.py and cant do a thing to change it. I think it is this that is not allowing me to heat the bed or the Hotend.
Resistance readings are:-
Hot-End Resistor 3.2 (meter set to 200)
Hot-End Themistor 332* (meter set to 2000)
Bed Heater 1.5 (meter set to 200)
Bed Themistor 1 (meter set to 200)

*Hotend assembly states "The thermistor should be about 100K at room temperature" - I'm nowhere near this

Apologies if my multi-meter readings look iffy - still havent mastered that side of things!

Here is the themistor setting from the connect sequence:-
echo:Thermistor settings: M304 Hh Bb Rr Tt, H0=Bed,

This is the feedback in the command line:-
ok T:304.7 /-273.1 B:23.8 /-273.1 @:0

As you can see the hotend temp reading is way off at 304.7c - and that 304 seems bit of a coincidence?

Other checks:-
Connection is normal.
Red flashing light on board is normal
All the motor commands are working as normal.

Edited 9 time(s). Last edit at 04/17/2013 03:57PM by spezzer.

A bit of help here? :-/

I'm going to try replacing the thermistor since the meter reading is way down. Anybody know where I can get a reasonbly small quantity in the UK within a few days?

Ok,
quote:
Hot-End Resistor 3.2 (meter set to 200)
Hot-End Themistor 332* (meter set to 2000)
Bed Heater 1.5 (meter set to 200)
Bed Themistor 1 (meter set to 200)


Hot end resistors are usually around 5.6 to 6.8 ohms
Hot end Thermistor should read around 100k at room temp (for a 100k thermistor)
Bed heater should read around 1.2 ohms - yours is probably ok.
Bed thermistor same as Hot end thermistor

All these measurements should be taken with the devices disconnected.

bugger - just got new thermistors - no difference. cannot understand why my meter is giving these reading for a 100k thermistor - im still getting 80-90 with the meter set to 200k.

worse still - i dont have a clue whats wrong with the printer - still getting cold reading of 304degs C

gonna try a reinstall.

i was going to try a reinstall then remembered i have an installation on my laptop. connected it up - exactly the same readings.

soooo to recap - software is fine - thermistor replaced - not getting the meter reading i was expecting - user error?

Edited 1 time(s). Last edit at 05/02/2013 04:48PM by spezzer.

80 to 90k is not far off 100k - depends on room temp as well. Your meter may be dodgy of course
What firmware do you use? I have only used Sprinter thus far so dunno about other flavours.
I am wondering if there is a short somewhere causing the software to read the thermistor incorrectly?

well now you mention it, it wasnt the most expensive offering from maplins but seems okay on other components. how do you test a meter I wonder?

however, i discovered one of my heat-bed connections looking somewhat iffy so re-soldered that. didnt make any difference but i also need to check the nearby resistor as i have been testing the heatbed thermistor with the resistor in line. i will isolate the thermistor and test that and then the resistor, i understand the resistor will affect my readings.

i'm with you and think i should be looking for a short but need to figure out what to test.

as for firmware - you got me there - it's been up and running for a few months but i suppose something can hasppen to firmware? i'm not sure what install it is - whats the easiest way to identify firmware?

When Pronterface connects to the printer, the returned message on the right window will display "Sprinter" for example- if that's what you have.
Not sure what you mean by "testing the heatbed thermistor with the resistor in line"? The thermistor connects directly to Ramps, not through any heatbed resistor. It may help if you bump this topic onto the "General" forum tab to get some more ideas.

this is my startup (below) - guessing the firmware is Marlin? tbh i enjoyed the build and the printing but software and firmware i've not paid too much attention to. and yes the resistor is nowhere near the heatbed thermistor- just me forgetting how i built it in January! i was able to change the thermistor settings to bring the temp reading down but that just screws with the other settings. i've added the [check temp] echo on the end.

just a thought - the M105 command returns way off values - is this anything to do with thermistor tables?

Connecting...
start
Printer is now online.
echo: Marlin 1.0.1 RRP
echo: Last Updated: 2012-12-07-JMG | Author: RepRapPro
echo: Free Memory: 11527 PlannerBufferBytes: 1232
echo: Using Default settings:
echo: Steps per unit:
echo: M92 X91.429 Y91.429 Z4000.000 E875.000
echo: Maximum feedrates (mm/s):
echo: M203 X300.000 Y300.000 Z3.000 E45.000
echo: Maximum Acceleration (mm/s2):
echo: M201 X800 Y800 Z30 E800
echo: Acceleration: S=acceleration, T=retract acceleration
echo: M204 S1000.000 T1000.000
echo: Advanced variables: S=Min feedrate (mm/s), T=Min travel feedrate (mm/s), B=minimum segment time (ms), X=maximum xY jerk (mm/s), Z=maximum Z jerk (mm/s), K=advance_k
echo: M205 S0.000 T0.000 B20000 X15.000 Z0.400 E15.000
echo: M206 X0.000 Y0.000 Z0.000
echo: M208 X210.000 Y210.000 Z140.000
echo: PID settings:
echo: M301 P12.000 I2.200 D80.000 W125
echo: Thermistor settings: M304 Hh Bb Rr Tt, H0=Bed, H1..n=nozzle, b=thermistor beta value, r=series resistor, t=thermistor resistance as 25C
echo: M304 H0
B3480 R4700 T10000 M304 H1
B3960 R4700 T100000
FPU Enabled no
transform correction not enabledecho : SD init fail

SENDING:M105
ok T:302.8 /-273.1 B:26.3 /-273.1 @:0

Edited 1 time(s). Last edit at 05/05/2013 06:47PM by spezzer.

Yep, its definitely Marlin and that's where I come unstuck as I have no experience with it.
Anyway, the return you got from M105 seems to suggest the heat bed is okay at 26.3C. However, the hot end reading may mean a short in the thermistor circuit. What I would do is disconnect the thermistor plug from the RAMPS board (T0) and stick your meter on the terminals of the removed plug (not the ramps pins) and see what reading you get. If its near 100k then that part of the circuit would seem to be fine - the problem may then be the RAMPS board itself, perhaps a blown capacitor shorting or summat.

just a quick look ( rushing off to work) shows your firmware as expecting a 10k resistance for your bed and a 100k resistance for your hot end ??
echo:
M304 H0 B3480 R4700 T10000
M304 H1 B3960 R4700 T100000

Right heres what i have in my config.h re temps

#define TEMP_SENSOR_0 1
#define TEMP_SENSOR_1 0
#define TEMP_SENSOR_2 0
#define TEMP_SENSOR_BED 1

The explanation text in my Config.h is as follows

//// Temperature sensor settings:
// -2 is thermocouple with MAX6675 (only for sensor 0)
// -1 is thermocouple with AD595
// 0 is not used
// 1 is 100k thermistor - best choice for EPCOS 100k (4.7k pullup)
// 2 is 200k thermistor - ATC Semitec 204GT-2 (4.7k pullup)
// 3 is mendel-parts thermistor (4.7k pullup)
// 4 is 10k thermistor !! do not use it for a hotend. It gives bad resolution at high temp. !!
// 5 is 100K thermistor - ATC Semitec 104GT-2 (Used in ParCan) (4.7k pullup)
// 6 is 100k EPCOS - Not as accurate as table 1 (created using a fluke thermocouple) (4.7k pullup)
// 7 is 100k Honeywell thermistor 135-104LAG-J01 (4.7k pullup)

Reading your feedback "echo" is that your firmware is expecting a 10k thermistor on your hotend ( option 4 in the text above)

hope this helps

progress - I have a 10k on the bed and a 100k on the head. i think that's what the settings reflect although did tinker with them in an effort to get the readings to make sense. definitely didn't save the new settings though.

but - did as suggested and measured disconnected from the board and the meter gave me 10 and 100 as expected.

i'm guessing this means the board is the suspect in this? do reprappro do warranty replacements?!?

how would i check the board - btw - whats does ramps stand for?

Edited 1 time(s). Last edit at 05/07/2013 03:21PM by spezzer.

Im still not convinced its your board. Lower resistance = higher reading Double check your wiring. Partial short ( to ground) would give high readings in theory.
With somebody that has both thermistors as 100K i would say swap them over at the board just to see if the problem moves as well but yours a different so no go. Can you rig the thermistor directly to the board? Bypassing your wiring ?

Im afraid i dont know what ramps means

Good luck

Updated Marlin firmware this eve using arduino-1.0.4 - it was a valuable exercise but didnt fix the problem.

checking meter readings down the board:-
hotend 100k thermistor - 99.9
heatbed 10k thermistor - 10.7
z-stop - open/close - 1/0.3
y-stop - open/close - 1/0.3
x-stop - open/close - 1/0.3
hotend resistor - 3.3
heatbed - 1.3
power (disconnected!) -1
fan - 1
...and motors responding correctly.

Edited 2 time(s). Last edit at 05/11/2013 06:30AM by spezzer.

Got this response from reprappro dot tech at gmail dot com...

Hi Spezzer

It sounds like the Analogue to Digital Converter on the Arduino chip has blown; this controls the temperature sensing. This usually happens when there's a short between the thermistor wires and 12V, for example at the hot end connector. The problem is that there is always 12V running to the hot end; it is switched on and off by the MOSFET, but it is switched on the ground side.

To test, remove the wires from the hot end heater screw terminals. Swap the bed and hot end thermistors, and connect via Pronterface to the board. You should get odd readings for the bed and hot end - though the hot end may still be stuck at 304.7C. Recalibrate the temperature monitoring for the different thermistors by typing:
M304 H1 B3480 R4700 T10000
M304 H0 B3960 R4700 T100000

The bed thermistor should show the correct value. What is the hot end temperature?

Regards,

RepRapPro tech support

I went ahead with the test and turns out to be the temp sensor on the board. Apparently its a surface mount soldering job followed by bootload flash then firmware flash which are way beyond my skills and tools!

So next - pay to have it repaired (£???), buy a new board (£90), or upgrade to tri-colour (£250+).

Anyway - that answers that one - eventually. Hopefully the thread contains some useful info ;-)

@spezzer: good job you know someone who can do SMT soldering?!

nice job droftarts