Remember the yellow switch with the chip out of it from earlier on in the thread, when I properly got it back together I realised that nothing worked, not a single button was registering any inputs and it had a persistant hum in its audio circuit and no sound output. Tonight I decided to fix it and I am going to show you how, something a bit different...
A little video of the problem:
Now this was a switch that has already had it's pmic and port replaced so has had some previous IC damage which I fixed enough to at least get it powering up. So before we start parts so far are port, pmic (m92t36) and a new daughter to mainboard flex cable as the previous one was torn.
So troubleshooting, first thing I did was checked for continuity across mainboard to daughter but only all the top pins and everything checked out... plus none of the buttons on mainboard are working regardless so from previous switch comms issues, I made a couple of pinout diagrams for the lite main to daughter fpc, i did this about a year ago to help the community but if I never posted them in here, well here they are:
These are going to come in super handy in a moment, anyway the switch works by sending button presses to a 32bit arm cortex mcu which then offloads to the cpu, it is the first port of call for 99% of button presses, I know this because of my destruction of switches in the name of finding out a number of things 1) how many chips can you remove and still have it boot? The answer is surprisingly a lot. and 2) what do some of the chips I don't know the function of do? well the STM32 chip was one of those again about a year ago so next that is where I turned my attention...
This is the chip:
Checked it over, everything looks fine, signs of flux on the board but the board has been reworked by somebody else and now me so thats not uncommon, It doesnt look like anybody has been here, so lets swap it and see what happens.
Chip off, came off nice and clean...
New chip on, happy enough with that could have been a little straighter but, aye, its connected.
And this is the result of the chip swap:
So mostly good but dpad up doesnt work... meh, dpad up is on the daughter and we have a new flex cable and a known good daughter... so it has to be the mainboard fpc, if we look at the fpc mainboard side we know the dpad up signal comes bottom row 8th pin across, and if you look at this picture notice anything off with bottom row 8th pin across?
So off with the fpc and on with a new one:
End result... switch lite did not defeat me