Hi, I’m currently also running into the failure 20 and after two evenings of trying to figure out what’s causing it I’m absolut clueless.
If i mention in the bottom part that something seems to be normal to me it’s just my impression. It’s my first unit so i could be wrong and the behavior is not normal
First the Board (latest 1.3): (24 pin header is the wrong way, but i fixed that with the cables)
Some things i’ve checked:
- Display and Leds work perfectly fine, but i get Failure 20
- things like low battery warnings work
- Tried it through the DC rail as well as through the battery connector
- the 5V and 12V pins on the top provide the equivalent voltage (5.1 and 11.94V)
- 7805 LDO = 5.011V
- 7809 LDOs = 8,90V
- went two times through the resistors in the Mosfet / LDO area and couldn’t find any fault.
When I hooked the Scope to the PA0 Pin on the Atmega it looked much different
So next I measure the 520N and the IRF9Z24 fets. All have 8,9V at the drain pin
Some scrope images from the gate pins
Both IRF fets (Q3 and Q6 look normal to me. Gate ~6.1V, Drain and Source 8,9V
(looks similar on both so i post just one of them)
520N Q2 and Q1 (for Channel 1) seems to be also normal (?)
(again both look the same)
But with Q5 and Q4 (for Channel 2) my headache begins
(they look both like that)
So next im measured the PB Line/Pin on the Atmega and the Gate of the 520N together
Channel A example like Q3 (yellow) and PB2 (blue)
Channel B example of Q5 (yellow) and PB1
That signal is so low and short that i’m not even sure it’s a real output of the Atmega
So now I’m really confused. If Channel A works as intended (which I guess, but don’t know), why don’t i get any signal from PB0 and PB1 to the mosfet gates of Channel B?
Or does the software check one channel after another, so there is a problem in Channel A which i don’t see so it doesn’t even trigger the test on Channel B?
I hope this post didn’t got too long Any help or suggestion appreciated.