S3#2 on which I re-flowed solder at the PCIE connectors and on the inside top of hashboard2/chain2, has been coming up with an x at Chain2#8. That was one, among others, that had been coming up x before the work. Now the S3, after running a day, will settle out at 426.xx with that ASIC x'd out. This has happened a couple of times. That difference from 441 is just about 1/32nd or what 1 ASIC puts out.
Someone said they had luck putting thermal conductive tape on all ASIC tops. Noting his work, I took conductive tape from a TO-220 and cut it down, put it on the single ASIC showing an x, and have just put it back up to run. It remains to be seen if the tape on that one ASIC, giving it a little more pressure than the other ASICs, pressing its underside harder onto the groundplane (if not well soldered under there) and tighter to the heatsink, will keep that ASIC from x'ing out.
This isn't working. After 2days it was down to 428GH/s so I rebooted and 9½ hrs later it's down to 424GH/s. What I notice now is that although Chain2#8 isn't x'd, it's a degree hotter than chain1 but the fan is running slower - chain1/2400/42, chain2/2160/43.
So, I tried to add a variable speed control to the pull fan and dial in same RPM's. Not only didn't it work but now I'm not getting the fan to run with a simple SPDT switch between 12v & standard out. Either my wiring is wrong or I fried something in the fan. The PWM controller has pos & neg for both IN and Mtr. I had made neg common for both. If the PWM pulls motor in below ground, e.g. intending the motor to be isolated from IN, then there may be a problem.
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No, I had put a strain on the fan wires and the connector to the hashboard, under the cover, had partly come free. Interestingly, when the S3 starts up the ground to the fan is disconnected. I know this because while the red led is blinking I can flip the switch from 12v (from the supply) to the internal fan speed output, the fan doesn't turn in either position. When the board starts hashing both fans start and the toggle from dictated speed to full speed works properly.
It may be that the PWM motor controller can work and that the internal plug had been partly separated already but I don't think so as the fan ran full blast ignoring my dialing down the rheostat on the PWM motor control.
After 8 minutes the chain2 fan was at 2220. I flipped the switch and the fan is now, well it was 4200 but has dropped to 3900.