Hi Rick

The possibilities are:
1) faulty thermistor
2) thermistor not making good thermal contact with hot end
3) wires to Arduino board faulty
4) fault with Arduino board
5) fault with Software

1) I read that you have already addressed 1) but how do you know the replacement thermistor is not faulty. I suggest you test it by measuring its resistance at room temperature and comparing it to expected resistance at room temperature.
2) Given you replaced the thermistor this is the most likely remaining possibility. You could wrap kapton tape around it and the hot end to try and give it better thermal contact.  I replaced my Solidoodle 2 hot end with one from http://e3d-online.com/E3D-v6. The thermistor is clamped into place so I am no longer left in doubt as to whether it is making good thermal contact. It is printing better quality prints and is more reliable than with the old Solidoodle 2 hot end. If you did upgrade I suggest you print out replacement mounting brackets whilst you still can. I ended up having to order replacement brackets from a commercial service.
3), 4) & 5) are unlikely and would take quite a bit of troubleshooting.

We are talking about a Da Vinci here, not an SD2. The Da Vinci is totally different from other printers.

In tegards to Ops problem and those with the same issue,  it is a design flaw. The heater has exposed wite near the core as does the thermistor as well. If you use the included metal brush to clean while powered one of three things will happen.

1) nothing, all will be clean.

2) power gets shorted to ground and blows the fuses ( zero ohm resistors) on the 12 volt line.

3) 12 volts get shorted to thermistor lead and shorts out the analog digital converter. This is the case with the Op snd others. Only solution is new board.

The possibilities are:
1) faulty thermistor
2) thermistor not making good thermal contact with hot end
3) wires to Arduino board faulty
4) fault with Arduino board
5) fault with Software

1) I read that you have already addressed 1) but how do you know the replacement thermistor is not faulty. I suggest you test it by measuring its resistance at room temperature and comparing it to expected resistance at room temperature.
2) Given you replaced the thermistor this is the most likely remaining possibility. You could wrap kapton tape around it and the hot end to try and give it better thermal contact.  I replaced my Solidoodle 2 hot end with one from http://e3d-online.com/E3D-v6. The thermistor is clamped into place so I am no longer left in doubt as to whether it is making good thermal contact. It is printing better quality prints and is more reliable than with the old Solidoodle 2 hot end. If you did upgrade I suggest you print out replacement mounting brackets whilst you still can. I ended up having to order replacement brackets from a commercial service.
3), 4) & 5) are unlikely and would take quite a bit of troubleshooting.

I have seen a couple of reports of this issue but no one seems to have a solution.

Monitor reports 10'C even though hot end is getting hot when you try load filament or set to auto heat.

I replaced the thermistor because it didn't look great.  Exactly the same issue, monitor still says 10'C while the print head got hot enough to crack the high temp JB weld I had put it in again.

I purchased a new print head, exactly the same issue STILL!  I have checked the main board and connections at the back, nothing looks to be wrong, everything plugged in correctly no other apparent issues.

Tks!