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

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.