I am new to electronics repair and got a non functional nintendo switch lite from eBay which had a damaged USB-C port. I have replaced the port (and MAX17050 since it flew away while replacing the port) and now it turns on and charges but it has very high battery drain (it will go from 100% to 0% overnight in standby mode).
I checked the board again and found that the 1.8v line is shorted. (only 5ohm resistance on cap next to pin 18 on M92T36 chip) and now I am a bit lost. The rest of the caps around this chip show no shorts and normal values.
When plugged in, I can measure 1.8v in this cap. Also found shorts in other caps connected to 1.8v rail.
Could this be an issue from the M92T36 IC? Also BQ readings seem normal according to other threads I’ve read in this forum.
Thank you in advance for your help
Can you take photos front and back of the board, good quality, so I can take look (maybe something will stand out)
Use an image host and format like
imageshack (dot) com/yourimage
Makes sense without the fuel gauge and also because of the short to ground on 1V8PDR
Now you have identified the fault, refrain fom plugging in / connecting battery etc until the short is cleared to avoid further damage
Thank you for your reply. I uploaded some pics here:
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ibb . co/QFggTFV
ibb . co/hBY638X
ibb . co/hCJVWcP
ibb . co/ZKbf4Gm
ibb . co/D4JLx6Q
ibb . co/jfCsrhW
I think the switch had been opened before as some screws were missing.
I also tried troubleshooting by undoing my changes (removed port and MAX17050 but the short was still there)
Did the short to ground on 1V8PDR only occur after you did the USB port / fuel gauge rework?
I’ll attach images so others can easily see them
Nothings jumping out to me in the photos apart from possibly a few areas where I might see (hard to tell) stray solder spatter
Can you pop this shield off and provide a photo, don’t clean it
To be honest I did not check it before replacing the USB port. I saw that some pins were missing/broken there so I replaced it straight away.
I saw some signs of rework around the EN IC. Is this connected somehow to 1V8PDR?
I’ve got a donor board (BSOD) that does not show a short on 1V8PDR so I could get some readings there
I see. Given that the USB port had issues, it’d probably be wise to pull the M92 IC off regardless, as typically M92 IC will fail in USB bent pin scenario. Then might be worth checking resistance to ground again on 1V8PDR to see if anythings changed.
Indirectly, pullup lines. Have a look on edge and see if anything jumps out at you as being wrong.
I also noticed, the Fuel gauge IC which was on previously is damaged and will likely not work, so might be worth ordering some more of these (from mouser, digikey etc) for future.
Don’t worry about this just yet. If your reading approx 5 ohms to ground it’s pretty clear cut that somethings up.
Failing all the above, my thinking prior was perhaps WIFI IC shifted during USB rework due to overheat or minor knock during reflow, but looking at your image nothing looks all that bad and as you didn’t get the readings prior it’s hard to say
Bad news. Removing M92 IC didn’t fix the short. However, when I tilted the board a little I was able to see some solder balls under the WiFi IC, is it worth to try to reflow it?
I do not have more time to work on it today so I will continue tomorrow with whatever suggestion…
I’ve got some spare MAX17050 already so I could use that in case we can fix it.
Thank you again for your help!
What do you mean? do you mean you saw solder balls out of place or bridged?
Nevermind. I compared it to the other board I have and it looks ok as you said.
I am not sure what I can do next. I have inspected the board but I can’t see anything out of normal
I guess you could hook up a PSU to the shorted rail and see if you can find the culprit via heat… though, I’m not a fan of this method so early on, that, and 5 ohms is going to generate very little heat, particularly if it’s an IC responsible, so you’d be better off maintaining a consistent ground, going round the board at various 1V8PDR locations (approx 5 ohms to ground) and seeing which area of the board represents the lowest reading to narrow it down.
Just before this though, can you also check resistance to ground on the big 2R2 inductor by BQ IC just so i can rule that out. Also resistance to ground on 3V3PDR (caps near EN IC)