Given that the Spartan 6 150's on other mining boards burn ~10W and only run at ~27C under a small (40mm squared) heat sink and moderate airflow, I would have thought that the Kintex is far more likely to be running at around 30C than 70C. If it is burning 10W then that heatsink and fan would have to have a thermal resistance of 5C/W to get the chip that hot - and that's pretty crappy for a heatsink with a fan...
As I remember Spartan-6 has no internal temp measuring, isn't it? My Spartan-6 boards on by both mq boards said round about 40 °C at room temp of 25 °C = 15 K difference. But they have an gpu cooler with an 6cm diameter.
The KC705 cooler with running fan tastes more than 40 °C (my finger means it's nasty warm, not to leave them to long on the cooler). So the internal +50 K looks like is a fact.
I checked the coolers stats from malico.com.tw web site (30x30x6 = MLT30-06) which I've measured. The stats says for that cooler an resistance of 4.82 K/W @ 200LFM to 2.4 K/W @ 600LFM. I'm unshure whats LFM means.
The Fan is 30x30 mm
2. I've found an titan TFD-3007M12S which could have 5m
3/h (2,95cfm).
I guess with values + internal resistance ~ 4K/W at >12W on chip looks like is not so much aside from you calculation.
The cooler on MMP K7 boards which runs only on 350 MHz because of the limited pdc tastes warm round about <40°C, but not hot. With <8W and reported internal 55° C that's consistence to the KC705.
I will search my PT100 thermometer to check the temp later on cooler, but I guess that the high results are a fact.
I tried to start chipscope but never did this before and have problems how to do that