It seems that we kind of missed something important in the silent modification of the Jasminer X4 1U miners described here and that is to take into account the one other thing that generates heat inside the miner. That is the controller chip on the miner’s control board that normally does not come with a cooling heatsink on top of it. The Xilinx Zynq-7000 SoC (XA7Z020) used is not a traditional FPGA like we kind of assumed without properly checking the specs of the chip. It is in fact a dual-core ARM Cortex-A9 Application Processor Unit (APU), and as you know having a processor, even a lower power ARM one can get things hot when operating and under load 24/7…
So, what apparently happened during the night, with no one present around the miner is the control board of the Jasminer X4 1U that we were using for testing just dying on us for no apparent reason. The only thing that comes to mind is the chip overheating for some reason and dying on us, although the normal operating temperature does not seem to suggest any overheating issues. Normally, when the miner is in its original package inside the 1U box with all the high-rpm server fans the inside ambient temperature is probably lower and thus no additional cooling has been provided for the controller board’s processor, but when you open it up and modify it to use silent fans things might become different. Thankfully we’ve had a spare controller board already ordered just in case something like that happened, so we replaced it immediately and the miner continued to function like before.
We’ve measure the operating temperature of the Zynq APU on the new controller board and it is nowhere near dangerous levels for such chips, at around 52 degrees Celsius (125.6 F) it should be pretty much safe even without extra cooling, right. Well, it might be now, but if what for some reason this temp rises for a while, probably that is what happened for some reason with the APU getting higher load for a longer period of time resulting in overheating (thouhg it could also be some totally unreleated reason as well, can’t be sure). Just to be on the safe side, it is a good idea to add a small memory chip cooler on top of the Zynq APU in order to keep the operating temperature lower at all times. Especially if you plan on using a silent modified miner and the the standard configuration where the issue could be less prone to appear.
Also, a good advice might be to order a spare controller board just in case, especially if you are running more than just a single Jasminer X4 1U ASIC miner. This is to avoid possible downtime in case something happens with the controller board on your miner. Do note that you can connect multiple hashing boards with Jasminer X4 ASICs to a single control board (our both had 3 connectors for hash board), though we’ve seen board with more connectors as well. We’ve tried and the control board detects and functions with a hashing board connected to all of the three available ports. So, as a temporary solution you might use a single control board to drive multiple hashboards of multiple miners in case you have more than juts one and you get a dead controller board.