Having problems with temperature readings

Hopefully someone can help me out here...

I have a Sanguinololu 1.3a board with 4.7k pullup resistors installed.
I have a J-Head hotend MK V-BV (the real deal, not a knockoff)

The hotend has a 104GT-2 thermistor installed.

The problem that I have is that it reads values, just not correctly.

For instance...
repetier host is set to: 255C
The Thermistor reads: 235C in Repetier
My meter says the temperature is 172C

I think my meter thermocouple is the most accurate considering it seems to follow the melt point of the plastic.

Any ideas why this could be so far off?

Thanks,
Jason

Mostly likely your using the wrong thermistor table in your firmware

In marlin it should be a type 5.

If it is type 5 in marlin, then check that there is 5v on R9 and R10 (also goes threw to 5v pin is ISP header, so easy to check)

Also check the resistance of the thermistor (while unplugged from the board) , it should be near 100 kOhms at 25c (room temp, more or less)

Edited 1 time(s). Last edit at 04/18/2014 06:43AM by Dust.

I guess I should have mentioned that I was using repetier firmware.
The table is set to a type 8.

I will meter what you mentioned and report my findings in a little bit

The thermistor ohms out to 100k or pretty close to that at room temperature.

I am getting 4.98vdc at the rail.
The only thing I did notice is that the resistor value on R9 and R10 is 4.61 Kohm

I may try to make a custom table with the beta value and resistor value to see what it changes with the readings

Yeah... still open to suggestions...

The temperature reading is even worse now!
I used the beta reading of 4267k for a 104-gt2

Hi I have put together a Prusa Mendel Printer, it has a Sanginololu board, the kit came from Amozn. All it does when it is powered is to move the x and y motor a few steps in each direction and back again. So the board must have a boot loader! and some sort of a program. I have a new Atmega chip and a Arduino uno. I have arduino 1.01 version and have added gen7 to it. I am using the Arduino with it chip in and using the MSo MSI pins The Arduino has a 1284 board listed and I was able to burn a bootloader and write blink to the new chip. I have tried to compile sprinter It reports an error Cpp:28:/pin.h:439:3 .
It will compile using 2560 mega !
Can Anyone Help ! I do not Know what I need to Do.
Thanks Alan.