SuperMicro Atom C2000 fix (5018A-MLTN4 with A1SAM-2550F)

We've had a number of Atom C2000 machines die during the past 1-2 years. The most recent one ran continuously since 2015 until 2020/05. The randomly dying machines are SuperMicro 5018A-MLTN4 with A1SAM-2550F motherboard.

Via EEVBlog we now found this simple fix. And it works!

Amazingly SuperMicro or other vendors don't seem to advertize or talk about this simple fix very much...

1 MOhm, 4 MHz photodetector

One-Inch-Photodetector (https://github.com/aewallin/One-Inch-Photodetector) with 1 MOhm transimpedance, a larger Hamamatsu 5791 photodiode, and OPA657 op-amp.

Achieves around 4 MHz bandwidth, which should be OK for intensity monitoring etc. This will work only for quite small powers, since the maximum DC output swing is 5V, corresponding to a 5 uA photocurrent, or around 12 uW if we assume 0.4 A/W responsivity for the photodiode.

Again I needed to tweak the TIASim simulation to make the experimental data fit the model. I now suspect this is due to capacitive loading of the op-amp output. This should be possible to test by connecting the detector directly to the Spectrum Analyzer input, and then adding successively longer cables and seeing if the response changes.