Got this previously worked on board as a challenge, it came dead with a badly soldered BQ.
After replacing, got 15V 0.5A (thought I was done with this board), but still no power.
Noticed a short near the MAX77 bellow the CPU (shorts highlighted in yellow).
What could be causing this short?
Thanks!
I would assume the MAX77 itself.
UPDATE: The caps near the other MAX77 next to the CPU are also shorted (circled blue).
That makes me discard the possibility of a bad MAX77 (correct me if I am wrong).
What is the resistance on these caps? (rather than just “shorted”)
You’re right, they are not shorted (they do give me resistance).
Now I’m kinda lost, no obvious fault visible, can’t find any shorts.
Tried other screens, housings and batteries, still no signs of life.
Please provide the readings though, so I can compare with a board I have.
I should also point out that the board goes directly to 15V 0.5A when I plug it in, I feel like it is actually turning on but shows no signs of life. Connecting it to a dock does not show anything whatsoever.
Ok, so on my board, those caps are all in the Meg or K ohms depending on polarity. What’s your resistance to ground at the 2R2 coil?
The coil is fine, 0 ohms.
0 ohms to ground on that coil? Ok, you have a dead short on your Sys rail. Do you have a thermal cam or anything that could detect what gets hot?
my bad, the coil has 0 ohms of resistance in itself and open line to ground.
Unfortunately, I do not own a thermal camera. I do feel the BQ getting hot fast when I connect the charger.
OL to ground doesn’t sound right either. There can be a lot of flux around that coil, maybe try testing the large cap next to it instead. Given BQ getting hot I would start there, it can cause SYS rail shorts. Remove it and then see if the shorts at the MAX IC are gone before replacing.
I also feel like this is important:
It is getting detected by tegrarcm.
I will try to remove the BQ ic meanwhile.
Is that even with the eMMC connected?
Yes, it is connected.
Any change to the resistance value on the shorted caps with it removed?
BQ out, short gone. Seems like it might be causing the problem. Will resolder a new one from a donor.