04-25-2021, 07:56 PM
For a reference, and for not wasting the images I've already created, 
attached are three excerpts from the combined schematics of the SOPine, Clusterboard, SOPine Baseboard, and Pine A64-LTS boards. The images show the wiring diagrams of the RTC power supplies, coming either from the PMICs or the batteries.
It's rather interesting to compare those three excerpts, especially the Schottky barrier diodes. The SOPine Baseboard shows the OD4 diode (the second barrier dioe) as N/C and shorted using a separate trace, which is correct because the actual second barrier diode (OD4, again) is located on the SOPine module. Thus, the SOPine Baseboard actually does the thing right with a SOPine module installed, having a total of two barrier diodes in place (OD3 on the Baseboard and OD4 on the SOPine). The Pine A64-LTS board also does the thing right: it has two barrier diodes, OD3 and OD4.
Then, why does the Clusterboard do it wrong, by having no second barrier diode? My guess would be that it had the other barrier diode at some point in time, and the testing probably discovered that the reset of SOPine modules didn't work. As a quick'n'dirty fix (or as a test?), Pine64 removed the second barrier diode, allowing full voltage from the batteries to reach the SOPine modules (and erroneously allowing the batteries to become charged, and to get discharged while the Clusterboard is powered on). The reset worked after the fix, and they probably simply forgot to make it right later.
attached are three excerpts from the combined schematics of the SOPine, Clusterboard, SOPine Baseboard, and Pine A64-LTS boards. The images show the wiring diagrams of the RTC power supplies, coming either from the PMICs or the batteries.It's rather interesting to compare those three excerpts, especially the Schottky barrier diodes. The SOPine Baseboard shows the OD4 diode (the second barrier dioe) as N/C and shorted using a separate trace, which is correct because the actual second barrier diode (OD4, again) is located on the SOPine module. Thus, the SOPine Baseboard actually does the thing right with a SOPine module installed, having a total of two barrier diodes in place (OD3 on the Baseboard and OD4 on the SOPine). The Pine A64-LTS board also does the thing right: it has two barrier diodes, OD3 and OD4.
Then, why does the Clusterboard do it wrong, by having no second barrier diode? My guess would be that it had the other barrier diode at some point in time, and the testing probably discovered that the reset of SOPine modules didn't work. As a quick'n'dirty fix (or as a test?), Pine64 removed the second barrier diode, allowing full voltage from the batteries to reach the SOPine modules (and erroneously allowing the batteries to become charged, and to get discharged while the Clusterboard is powered on). The reset worked after the fix, and they probably simply forgot to make it right later.