Troubleshooting broken companion boards
Three boards
- 76, failed in Stale's battery in the field - does not run LEDs, SOC output is wrong
- 99, exhibits wrong SOC value
- 100, exhibits wrong SOC value
Nr. 99
At 37.03V input from the PSU, the scope measures
- 8.42V @ SOC
- 11.95V @ 12V
- 3.38V @ 3.3V
Can do 10.13V on the SOC output if the input is 42V
Now that I think about it, I remember that the PWM was wrong too, we have decided that last time.
So it is the input stage. Maybe the noise? Input filter?
To test this hypothesis, measuring with a battery:
- 35.03V input
- 5.9V SOC
- 20 mV noise
- D = 56.08%
EXACTLY the same result w/ PSU, except way more noise, around 400 mV.
R4: 1.82V
Nr. 100
5.45V SOC on the same conditions as above.
D = 52.16%
R4: 1.82V
Nr. 76
Nothing on the SOC, but the supply voltages are OK.
No PWM.
Re-uploaded the code - still nothing.
FUCK I forgot to remove the 48V jumper..
Now 3.8V on SOC.
D = 36.08%
Woooohoooohooo.
New start
33.5V input according to PSU, 33.67 in reality
Measuring R4: 1.82V (scope) on both
38.04% on 100
|
|
76 |
99 |
100 |
|
R4 w/ scope |
1.82V |
1.82V |
1.82V |
|
D |
21.18% |
42.75% |
36.08% / 37.65% |
I reflowed 99. Now I get 49.8%!! 47.08% after I reflowed all legs again with a soldering iron.
Trying to remove parts on nr. 100
- Removed C4 - no difference basically
- 2.2 uF - should be 0.1uF!!
- Removed R4 - no SOC
- Replace with zero Ohm - back to 5V :(\
- Swapped the chip - no difference
It is suspicious that C4 was bad - maybe also C5?
C5 was also 2.2 uF!!
Swapped to 0.1uF, everything is perfect. ^^
On Nr. 99, C5 was also 2.2uF. Swapped to 0.1uF. Fixed!!
Explanation
C5 is the AREF capacitor for the 328PB, if it is too high, the voltage reading does not work right.