Hardware 2-3 hot components. Two shorts.

flabbaba

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Hi everybody,

So I have a waterdamaged unit that I don't seem to ba able to fix. When connecting the charger I draws .19A at 15.1V
At that moment two or three components start to get pretty hot and I'm unable to touch them. I tried to remove them from the circuit, but both shorted sites remained shorted.
I have replaced the BQ2, the M92 and the 13USB. Even the Max77 chip. But to no avail. I also removed the USB-C.
The shorted cap close to BQ2 is still shorted at the pads when I remove the capacitor. The same is the case with regards to the capacitor at M92. Its stil a short when I remove the capacitor.
I even used a few hours to remove the SoC, reball it and put it on again. None of the shorts dissappeard when removing the SoC.

Does anybody have any suggestions?

And there's a missing inductor on the backside, but that should not have anything to do with the shorts.
 

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flabbaba

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Thank you so much.I'm not so sure how am supposed to make use of this, or what conclusions I should make from my findings. I would really like to know how the shorted capacitor around the BQ chip traces out on the mainboard. As you can see in this next picture. The red part has now become ground-plane. I am not able to figure out where this happens.
 

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Mightyjebus

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BQ24193 voltage.jpg

Here's the pin outd for the BQ IC. pins 17 & 18 in your picture are GND pins so they should be grounded or 0v

ignore the voltage readings on the picture as they are from a problem I was having#
 

flabbaba

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Ok. I think I will use it for parts instead...
Look. All capacitors next to the MAX77 IC is also having shorts. Also after removing the IC.So forget this. I dont't think this board is worth the hassle.

--------------------- MERGED ---------------------------

View attachment 215198
Here's the pin outd for the BQ IC. pins 17 & 18 in your picture are GND pins so they should be grounded or 0v

ignore the voltage readings on the picture as they are from a problem I was having#

Ok, but the pins in question are 15 & 16. They are grounded too, even without th IC, and I'm not sure where they go.
 

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flabbaba

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try continuity through the coil near the BQ chip and also consider swapping the BQ IC
The coil is ok. Shouldn't the short on pin 15&16 to ground go away when I remove the chip? I mean, why replace the chip if its still shortet with no chip installed? Not want to fry another...
 

Mightyjebus

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SYS 15,16 P
System connection point. The internal BATFET is connected between BAT and SYS. When the battery falls below the
minimum system voltage, switch-mode converter keeps SYS above the minimum system voltage. (Refer to Application
Information Section for inductor and capacitor selection.)

from the manual for the BQ IC. Possibly pins 15 & 16 connect to the "hot" IC's above the charge port. Might be worth buzzing them out to see if there is a direct connection or remove them to see if the short goes
 

flabbaba

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SYS 15,16 P
System connection point. The internal BATFET is connected between BAT and SYS. When the battery falls below the
minimum system voltage, switch-mode converter keeps SYS above the minimum system voltage. (Refer to Application
Information Section for inductor and capacitor selection.)

from the manual for the BQ IC. Possibly pins 15 & 16 connect to the "hot" IC's above the charge port. Might be worth buzzing them out to see if there is a direct connection or remove them to see if the short goes

Removed all 3 of them. Still short.
And just to recap - now BQ is out, the MAX is out, the power-FETs, the P13USB. And when the TEGRA was out alot of the shorts where also present. No liftet pads anywhere on the board. No more corrosion residue.
I want to thank you alot for your effort, but this might just be one of those lost cases....
 
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flabbaba

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Ok. So I have removed the SoC, the RAM, all the MAX ICs, and still the board is full of shorts in so many places. Can somebody give me a clue as to how this is possible? It was waterdamaged. Any shorted capacitor I desolder is fine outside circuit.

Can I inject voltage to see what happens? Where to inject?
 

WigWrm

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You have a short between VSYS and PGND, per the pictures you've provided. Pins 15-16 on the BQ are VSYS. Pins 18-19 are PGND.

Your ground picture in post # 3 is incorrect. What you have labeled as GND is VSYS. The red area in the picture is PGND. I would try removing the coil next to the chip where you removed the capacitor. If that doesn't remove the short then this will become complicated. There are vias on the VSYS shape and if you are lucky they will be through hole and connect to the other side of the board. You''ll have to keep tracing VSYS and removing components...

Or get an IR temp gun and find the hotspots when you apply power. Easiest way to find a short.

You would apply a very low voltage to the VSYS rail and keep your current limit on your power supply very high. This way you wont turn on the IC's connected to the VSYS rail but the shorted components should still get hot. You keep increasing the voltage on your supply until you see high current draw or your OC light on your supply comes on.
 
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flabbaba

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Anyway. I did remove the coil, and nothing happened. Not surprisingly, since a coil should have continuity.
So I went to inject voltage into those point where the capacitor was. I put current to 200 mA and increased the voltage from 1 and up to 5 volts. Then I could feel one are starting to really get warm. I put some alcohol on the spot and saw exactly what component it was.
I removed it - and seemingly all shorts on the board is gone! And this board had alot!.
So now I wonder what this component is. Does anybody know? It was clearly some corrosion under it from the water-damage, so maybe it isn't faulty.
And also I wonder what kind of inductors or coils are sitting close to this component.
shorted component..jpg

And now that this is sorted out, I realized I have really messed up the board. Yesterday I lifted the RAM and I wonder how exactly pads under the RAM is connected to the chip. I melted the solder pretty well, but maybe I lifted them off too early. I have bought a stencil for K4F6E304HB-MGCH LPDDR4 RAM and will try to add solder paste to it. But I want to ask if this is possible, or if the chips are damaged... My idea is that it will grab onto whatever contact point that is left in there and still work.
RAM.jpg

I have removed so many components on this board, and there is so much reballing to do. I am not sure if I can put everything together without one single mistake. I am dissapointed in myself that I did not try this before I removed so much on the mainboard.
 

Mightyjebus

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weirdly I got a water damaged switch today with a very similar problem. I've not checked out the IC you mentioned but I did remove the BQ, Coil and big cap we mentioned above and short was still there. Using a good board I checked for continuity from the shorted side of the coil and found that they it goes to a MAX IC just below eMMC board. The picture below shows the link. I've removed the MAX IC and the short has gone, just need to solder on a replacement to see if it fixes the problem
 

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flabbaba

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weirdly I got a water damaged switch today with a very similar problem. I've not checked out the IC you mentioned but I did remove the BQ, Coil and big cap we mentioned above and short was still there. Using a good board I checked for continuity from the shorted side of the coil and found that they it goes to a MAX IC just below eMMC board. The picture below shows the link. I've removed the MAX IC and the short has gone, just need to solder on a replacement to see if it fixes the problem
Lucky you. This was not the case here. As mentioned, I have removed almost all there was to remove :( Your board is not like my board. The area you mention is almost empty in my board with almost no components. Glad you found the fault :-) But how did you exactly find that out? On my board, before I found the culprit, there was like 30 shorted caps all over the board. Now it's none.
 
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Mightyjebus

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I find the rule of thumb with the switch is if a cap is shorted near a IC, remove the IC and see if the short goes. For my fault I just probed around a good board until I found continuity to the area I was having problems then removed the nearest IC to see if the short disappeared.
 
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