I have two TCL A30 phones.
Old Phone: This phone worked fine for years, then stopped charging If you plugged a charger into it, the phone would make the charging sound, the phone would tell you it is charging, but the battery icon would not have the charging symbol in it and the battery would not charge.I tried new battery, same behavior.
New Phone: Works fine, bought as a donor board to try and repair Old Phone
My interest here is to repair Old Phone, using components parts off New Phone if needed. I am not interested in replacing Old Phone with New Phone. I do not want to damage Old Phone any more. Right now the phone is usable but I have to charge batteries externally and swap them out every couple days. I would rather do that than risk ruining the device.
The first thing I tried was a USB port swap. I removed the existing port on Old Phone and put a new port I had on it. I failed to realize at that time that the phone has a "reverse" micro USB port, and the port I put on was a standard one, so the cable was flipped upside down and the pins were reversed when inserted. I inserted the cable, and nothing happened at all. No charging sound, no notification, nothing. I ordered a new reverse USB port, and put that port on. Same thing, insert USB cable, and absolutely nothing happens. I am 100% sure the port swap is good, I check continuity between the pads where the legs connect and the ends of a USB cable and it showed continuous. I tried plugging the phone in a PC, also nothing, the phone is not recognized.
I looked at the Old Phone board under a thermal camera with the cable plugged in, no components were getting warm
The way the phone is designed is that the USB port is on one side of the board, but all the component are on the opposite side. The opposite side has test points corresponding to the USB pins. I checked voltages on the test pads, and on New Phone, I found 5V on one of the pads (See Pic). On Old Phone, 0V.
How could I tell if that test point is where the USB leg come up from the other side of the board, or if the circuit runs through bunch of other components and then ends up at that test point? My thought is if the test point is the beginning of the charging circuit (so it went USB Cable > USB Port > Test Point > rest of phone) I could run a wire from the USB port leg to that test point and restore charging. But if it isn't, I would be bypassing potentially important parts of the charging circuit and could be sending power to the phone in a manner that could damage it. And how likely would it be for some sort of "internal trace" connecting the leg of the USB port to the test point to break? That's what leads me to believe the test point is at the end of the circuit and not the start. It also worries me that the phone is not recognized by a PC at all.
Sorry about the blurry photos I will try and get some better ones off my microscope later
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