Thermistor values suddenly changed?!

[Jesse McKenna]

Hi all.  Hoping someone might be able to make sense of a very strange problem I've run into.

Background:  I'd previously upgraded the default Lorei bed with an aluminum bed with a silicone heater.  The bed heater was driven via a MOSFET.  

Where things got weird:  My setup has been working great until I ended up with a print that simply stopped extruding mid-print, though if I remember correctly, the extruders had a higher Z value than where the print had stopped.  When I tried to print again, the firmware safety mechanisms were preventing me from doing so because the bed thermistor was reading 1 degree.  At the same time, the extruder one thermistor was reading 100 degrees at room temperature.

I tried swapping the bed thermistor for a new one, but still got the same readings - fluctuating between 0.9 and 1.3 degrees.

Next I tried reinstalling the firmware after double-checking all the settings.  No change.

I then pulled the controller board out and couldn't see any signs of damage.

I disconnected everything from the board and powered it on and here's what I see:

I'd never really inspected the board while it was powered on, but the D13 LED on looks suspicious to me.  Can anyone confirm which LED(s) should be on in normal operating conditions?

All theories welcome!  Thanks in advance.

[dayboy]

hi Jesse

i turned ON my lorei with all wire in place 

no led ON except 1 steady led(d3) in the center and 2 blinking led (d7-d8)  on the left of your picture near the rectangular chips

the d13 led turn ON when the fan of the hot end begin to be in use

maybe your little 20mm fan is dead or something in relation with it

good luck