Bed and extruder showing same temperature

I need help troubleshooting thermistors. Using Repetier host, both bed and extruder have the same temperature when 1) no heaters are on, 2) both heaters are on, 3)4) either one of the 2 are on. I tried:
1. Thermistors seems to be fine -- connected each one to ohm meter and get appropriate readings (100kohm @ room temp).
2) Connected only the extruder thermistor to T0 (bed not connected). Repetier host indicated identical temperatures for both bed and extruder even when heating extruder.
3) checked & double checked crimped pins
4) pin headers on ramps seem to be well soldered -- no visible shorts.

Before I contact my Ramps supplier, I want to rule out everything else. Can it be Repetier? or firmware settings? what else can I try?

Thanks.

Send M105 manually and see what gets reported. This graphical host stuff isn't exactly the best tool for debugging.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

The firmware could be miss configured so that the pins for both thermistors are the same... This would be weird, but is possible.

I would turn it off. unplug the ramps from the mega. unplug the thermistors and do a continuity check from pings 2 and 4 of the thermistor plugs. There shouldnt be one... pins 1 and 3 will be connected, as thats ground.

Also check for shorts on a13 to a14 on the mega

Thank You. There is a short (0.5ohm) between pins a13 and a14 on the 2560. Damn Sainsmart clone. I'm looking at the traces on the board under microscope and don't see anything obvious. I may end up butchering the board with my soldering iron. -- one option maybe to use T2 but I will need to modify the firmware. How easy is that? I'm having so many issues...

Thanks again!

Easy to modify firmware

edit pins.h for the section relating to your board selection (33 34 or 35)
Find [github.com]

#define TEMP_0_PIN 13 // ANALOG NUMBERING
#define TEMP_1_PIN 15 // ANALOG NUMBERING
and a little further down
#define TEMP_BED_PIN 14 // ANALOG NUMBERING

swap the numbers around as you need to...
eg
#define TEMP_1_PIN 14
#define TEMP_BED_PIN 15