i was able to fix my nano .
the problem was with the on board charging ic - ltc4054 .
this charger gets really hot , but its the way it works , as its got internal thermal protection at 120 *c .
i bought my dso on ebay (wasnt even aware it was made by seeedstudio) so it be a knock off .
this part should be marked as LTH7 , but mine was marked with a different number , so it might be a cheaper part , i dont know .
anyways , i bought the right part (ltc4054) from ebay , soldered it up , all works fine now .well . my dso looks bruised now , as all the panels are glued to it ,and it wont be the same after reassembly .
btw , it wont power up without battery , it just blinks constantly .maybe my usb port power is not enough , i dont know .
but it charges the battery fine now (and works from usb port) .
heres the pic of the part after replacement:
