Is my raspberry unrepairable?

Question

First of all I'm a beginner, so please don't judge me I know I did something bad. SO, yesterday I was trying to make my raspberry pi 2 B to work with an external battery. I took a lithium polymer battery with 3.7v and 2500mah and I connect it to a booster. At first I was trying to hook it up to the micro usb input on the board and it didn't work. Then I look in youtube and I saw people plugging external batteries into the gpio pins. I joined the positive cable into the the first 5v pin and the negative cord into the first 3.3v pin and vs. Although when I connected the positive cable into the first 5v pin and the negative into the 3.3v pin for the second time with longer time touching them, it sparked and then I saw it left a kind of cut in both gpio pins. Now this morning that I try to power up my raspberry with a normal micro usb cable, I can feel the board getting warm(normal warm) but the led does not turn on. In the pictures attached, the voltmeter says 4.12 v output but yesterday I adjust it to 5.2v also using the voltmeter but I don't know why it shows 4.12v now... And also in the mark on gpio is the same in the other side (the first 3.3v pin). Is there anything I can do? Or is it burnout forever? Thanks in advance. 
 Attachments:

Robert Peter Oakes · Answer

You have most lightly blown something on the PI The 4.3V battery should NOT have been connected between the 3.3V pin and the 5V pin, these are both seperate power + rails for parts of the PI board and you just put effectivly 8V into the 5V pin or caused excessive current to flow through pins not designed to have a difference of the battery or booster voltage. What you should have done is connect the batter or booster output to 0V for the black wire and 5V for the red one (Using the booster to give you the 5V you best option is actually to feed the 5V into the PI via the USB connection though, so battery to booster, booster to PI USB power connector the schamatics have not been published but based on your description of how you connected a battery capapable of providing many amps between the 3V3 and 5V pins I would expect something to have failed Sorry for the bad news, may the PI RIP. Peter

shabaz · Answer

Hi Mauricio, The warmth near the microUSB is a sign that something serious is wrong, because it means either the rest of the circuit is drawing excessive current (due to blown chips) or that the DC-DC converter chip which is located near the micro-USB connector is faulty. Either way, the parts are tiny (about 0.4mm separation between pins, and often the pins are on the underside) and most people don't have the tools to remove and replace them (and if they do, they charge around $75USD for soldering one part - and no idea how much to desolder and clean up the board of the existing one). By wiring directly to the 40-pin connector, any (little) protection the Raspberry Pi has was bypassed. Because the supply connection was made to 5V and 3.3V rails, there is a very high risk the DC-DC converter chip has fried itself, another sign of this is the sparks you saw on the connector pins - it means a lot of current went through. In summary, the entire board has to be replaced. I didn't read the entire detail, but if your power LED is not functioning then that near-guarantees that the DC-DC converter IC (or parts near it) have died, and they are not economically replaceable. Not the news you want to hear, but at least by reading the comments you've learnt the technical details about what could have occurred. As a beginner, after the first board or two, you'll be fine - experience means you won't trust all instructables etc., and will take some precautions such as double-checking pinouts.