6 hours ago
Motivation
Since some years my system (Rockpro64 V2.1 2018-07-02) is not starting properly after a power loss, with increasing occurrence. It seems after some hours of power loss (e.g. over night) it is working more reliable, but when waiting only a few minutes this is not working anymore at all. Only the power button can be used for startup my system reliable.
In the forum there can be find a similar thread with some general information about the schematic and some measurements with a new system. Many thanks to @Nikolay_Po for his investigations on a new board. This was the base for my investigations and I solved it finally. I will describe my work step by step now, so others can repeat it and hopefully fix there system. If someone can give me an advice how to add/upload pictures, I will add my photos, so you can see what I have done.
Repeat the same measurement
"PMIC" is measured on C205 (right side) and "VCC5V0_SYS" is measured on C2006 (left side). Both can be found on top of the circuit board. The measurement results nearly equal the results from "Nikolay_Po" (the colours yellow and blue are interchanged in my measurement). So, perhaps, not the discrete components has changed its behavior but something inside RK808 changes over time. Or, the original values of the discrete components are chosen very close to the borders of the PMIC-system. No matter what it is, we can only change the discrete components - C204 catches my attention first.
Measure around and modify C204
The capacitor C204 can be found on the bottom of the circuit board (SD card slot at bottom left), in the area between C164 and C168, left of the resistor R89 and over the resistor R88. Another description: between the both big capacitor (C164 and C168) there are 4 small components in a flipped L-shape. C204 is the one in the corner of the "L".
The measurement was done with 2 channels, connected left and right of the C204 component. This means one is "VCC5V0_SYS" and the other one is the connection between C204, R89, D5 (soldered on the top side) and R88.
Try to increase the capacitor C204
Because it was working with a brand new board, most likely some aging process has changed the timings a bit. A second capacitor will increase the peak and the time a bit and maybe this can fix the problem. I added two connectors with wires left and right besides C204 and was able to add a second capacitor in parallel with an alligator clip.
1. choose 1uF --> working 100%
2. choose 100nF --> working 100%
Fix by soldering a SMD capacitor on top of C204
I disassembled some small SMD capacitors from a old circuit board and found one with around 150nF. This part I soldered on top of the C204 capacitor and this really fixed the problem for now.
Since some years my system (Rockpro64 V2.1 2018-07-02) is not starting properly after a power loss, with increasing occurrence. It seems after some hours of power loss (e.g. over night) it is working more reliable, but when waiting only a few minutes this is not working anymore at all. Only the power button can be used for startup my system reliable.
In the forum there can be find a similar thread with some general information about the schematic and some measurements with a new system. Many thanks to @Nikolay_Po for his investigations on a new board. This was the base for my investigations and I solved it finally. I will describe my work step by step now, so others can repeat it and hopefully fix there system. If someone can give me an advice how to add/upload pictures, I will add my photos, so you can see what I have done.
Repeat the same measurement
"PMIC" is measured on C205 (right side) and "VCC5V0_SYS" is measured on C2006 (left side). Both can be found on top of the circuit board. The measurement results nearly equal the results from "Nikolay_Po" (the colours yellow and blue are interchanged in my measurement). So, perhaps, not the discrete components has changed its behavior but something inside RK808 changes over time. Or, the original values of the discrete components are chosen very close to the borders of the PMIC-system. No matter what it is, we can only change the discrete components - C204 catches my attention first.
Measure around and modify C204
The capacitor C204 can be found on the bottom of the circuit board (SD card slot at bottom left), in the area between C164 and C168, left of the resistor R89 and over the resistor R88. Another description: between the both big capacitor (C164 and C168) there are 4 small components in a flipped L-shape. C204 is the one in the corner of the "L".
The measurement was done with 2 channels, connected left and right of the C204 component. This means one is "VCC5V0_SYS" and the other one is the connection between C204, R89, D5 (soldered on the top side) and R88.
Try to increase the capacitor C204
Because it was working with a brand new board, most likely some aging process has changed the timings a bit. A second capacitor will increase the peak and the time a bit and maybe this can fix the problem. I added two connectors with wires left and right besides C204 and was able to add a second capacitor in parallel with an alligator clip.
1. choose 1uF --> working 100%
2. choose 100nF --> working 100%
Fix by soldering a SMD capacitor on top of C204
I disassembled some small SMD capacitors from a old circuit board and found one with around 150nF. This part I soldered on top of the C204 capacitor and this really fixed the problem for now.
