Switch Lite with weird shorts and one possibly blown cap

I pulled apart a Switch Lite recently that was charging (~0.63amp on the meter) but wouldn’t power on. Doing a bit of probing around the front of the board, I noticed a few odd caps that were registering a short (ImageShack urls broken up since apparently I can’t imbed photos or links):
https ://imageshack.com/i/poRWS6VTj
https ://imageshack.com/i/pm2oN7Thj
https ://imageshack.com/i/pmOWiW8aj

Looking at the back side of the board, I noticed a cap that appears to have exploded for what seems to be the backlight for the home button:
https ://imageshack.com/i/poenQnWBj

Does anyone happen to know, or could find out, the value for that capacitor on the back of the board that is blown? I’d appreciate it if so since details on these components seem to be hard to come by. As for the cap on the front of the unit, is that related to issue on the back of the board? I don’t have another unit to compare it with but I assume I shouldn’t be able to get a beep on the multimeter on both side of that thing.

I cleaned up the corrosion in that area and removed that cap but the shorts are still present. Any ideas as to what would cause a short on those cap? I did a ton of probing of caps and so far have only found those few.

0.63A would iimply that it is actually powering on, it’s possible your having display issues, likely at the backlight area or the connector, and/or passthrough, it might be worthwhile providing photos of this area, and also inspecting all connectors for signs of charring/burns

That’s an inductor, and it’s normal for it to read short to ground in this circuit.

I don’t have a Lite board to verify what rail these caps are on, but can you let me know the resistance across them?

It doesn’t look exploded to me, and would guess it’s actually fine, the area just has corrosion afaict

Thanks for getting back to me so quickly, Severence! You are totally right about that board powering on, I am just an idiot. I had too many of these things apart and thought I had ultrasonic’d the daughter board for this switch when in fact I did not and there is corrosion around the backlight connector and burned pin on the backlight ribbon. I’ve fixed one of those before so that shouldn’t be an issue. I plugged the board into another switch lite that I had with a main board that is probably dead (I’ll save that one for another post to see if it can’t be resurrected but due to the amount of corrosion I saw on the back of the board along with several shorted caps under the CPU I doubt it) and the screen came on with no problem.

I unfortunately lost that cap that I thought might have been blown with all the corrosion around it but I hijacked it off that one that is likely dead. How would I go about figuring out what the value is for that thing so I can order some replacements?

As for those 4 shorted caps(?) near the edge of the board on the back as well as that one on the front of the board that’s just north of the 4 on the back, they each measured 0.3 with the meter set to 200 Ohms if I left the probes on each for a few seconds. I probably need a multimeter that get a finer reading than that but unfortunately that is all I have to work with at the moment.

On second thought, looking at this ribbon cable for the backlight, just under half of the second pin from the left remains. The last one I fixed was burned somewhere in the middle and I was able to solder a jumper over the burned spot. Any suggestions for what to do with this burned pin with just under half of the pin remaining? I’m afraid that if I just solder a piece of jumper on there to act as a pin it might move and short out one of the other pins.

I have done something similar, let me pull something up

It works but I will be replacing mine because I fiddle with the LCD too much and cracked it

If were talking about the pads on the ribbon itself, then I’ll typically do a loop, burnish (to flatten it) tin with leaded, then use UV mask around which holds it solidly, don’t be tempted to use super glue or other.

Wish I could tell you the size of the wire I use but I just typically use the wiring out some old earphones which is the perfect size.

If were talking about the pin contacts within the connector… I wouldn’t, I’d replace the connector entirely.

If those caps are still showing as a dead short, I’d refrain from applying battery or USB until that’s resolved. On your other Lite board can you buzz the caps out to the next major IC, I expect these caps will be on the common rails 1V8PDR or 3V3PDR which can both be found at the M92 IC.

In order to select an approriate replacement capacitor, just measure the capacitance on one of the caps from your donor out of circuit, for size measure the capacitor with calipers for the standard size, voltage rating you just measure the voltage at the pads on the board then choose the next appropriate rating up from that,

I managed to repair the connector and masked off either side of the “new” pin 2. Looks pretty good too if I do say so myself :slight_smile:

As for tracing those caps back, I’m not having much luck so far. Looking at the board, on the opposite side (the front of the board) of where those caps are, in between both sets is the NFCDDR A921R9 BGA chip. Also of note, thought I don’t if it means anything, on the front of the board right next to where you can see trace for the 2 caps and whatever that dark gray piece is (what is that btw?) is a triangle test pad. Are they used as arrows to point to something or just something to denote ground? I’ll keep probing around and hopefully find a cap or test pad that they lead to that isn’t ground but so far that is all I have found.

Also of note in the pic above, the component that is at the other end of the arrow on the right is the one from one of the first pics I posted that was registering ground on both sides. Not sure if it is a cap or not but if so, I assume its related to the issue the other ones have.

Thanks for the tip! That might come in handy if I have one that is burnt any worse than what I was working on today.

Usually the triangle points at pin 1 of a nearby ic or connector.