My pi B+ worked fine for few months but now it isn't anymore. When it was booting fine, red power led stays on while green act led flashes while booting (suggesting that it is reading from the card). The last time I remembered doing was apt-get upgrade and could have some errors but did not take note of it. Afterwards, it cannot boot anymore. I know that my pi is faulty because I tried to replace the power supply (2) and sd cards (3) to no avail. With only the sd card and the 5v supply only connected to my pi, the red and green leds stay forever. I tried several things like applying a bit of pressure to the card hoping that would make the green led blink at least once but it stayed on brightly. This is the same thing when you remove the sd card and power it up.
Is there anyone here who knows how to resurrect my pi? I can solder well and can read schematics. I tried resoldering the sd card port portion and checked whether any pins were shorted or open but still not working. TIA.