I'm confused. Now they are giving us two temp readings. In the past, for the S7 and others have we just been seeing the pcb temp (labeled: Temp).
Then why now they showing us the chip temp. Why is that important now? Poor design?
My pcb temps are running 56, 56, 59 at 625M. On any other Antminer I would say there is plenty of room for some over-clocking. Or in this case to move to the default 650M. (EDIT)
Chip temps are 87, 86, 91. Are these temps higher than an S7 with the above pcb temps? In other words is there more of variance on this miner than the older ones. Where we can burn out a chip before the pcb gets to 80C. That's still the safety shutdown temp. I believe.
Inquiring minds want to know.
Maybe I will do some clarification here.
1) All previous chips until now are not able to read chip temperature because of missing temperature probe on chip die.
2) temp reading was done through temp probe at PCB, far away enough from chips to get much lower readings.
3) temp of PCB is extremely inacurate because it can't discover poor heatsink contact and chip overheat. PCB temp vs Chip temp accuracy is extremely affected by frequency (total heat generated) and fan speed. Low freq and low fan speed keeps PCB temp closer to chip temps.
4) generally, all chips follow the same temperature characteristic, so if datasheet says it is safe to operate the chip at 125C, it is true, because it is common to all other similar chips.
5) a lot of previous miners (S5 is the winner) suffered from high power density and poor heatsink contact, so there was big number of failed S5 due to overheating
6) knowing chip die temperature is the key to operate chip safely. Keeping the chip within safe margin keeps the chip running virtually indefinitely.
7) since antminer S5, all chips are able to withstand temperatures about 200C under load (under load is very importatnt). It is from my own experience when chips were running and due to overheat they desoldered themselves while soldering temperature is about 200C. Resoldering chips back was enough to fix the board. BTW: My Radeon 5970 GPU was working at 150C without destruction.
TLDR:
So, reading die temperature is the key to operate chips within safe region. Answers to your questions:
1) why so important: let us know key safety information
2) poor design: Yes, until now. With chip temp reading miners wouldn't fail.
3) are S7 temps lower/higher than S9: With the same PCB readings your chip temps will vary about +-10 degrees on both S7 or S9 miners. This is because PCB temperature is far away from chips and it is also cooled by fan. Depends on fan and frequency speeds.
4) OC suggestion: Keep your chips temp below 125C under any circumstances. Lower is better. From my experience chips can work even higher, but PCB componnents are aging and efficiency drops.
Hope it helped also others