SD card corruption

hello world,

i bought sd card, but sd card apparently has bad sectors. when i store files on it, practically every fourth file is stored correctly. all other files appear to be stored damaged. if i open those files as raw data, all bytes in them are set to 0s. so, that means that sd card got to have bad sectors.
if i run chkdsk app on that card, windows tells me that there are no problems and does not report any bad sectors.
this is supposed to be 4 gb card, but i suspect that it might be 1 gb card which was in low level format process formatted in factory to falsely report 4 gb. or it is of so poor quality that three quarters of it got corrupted. it is likely that one of this is problem, since this sc card was ultra cheep. it was only 3 dollars for 4 gb. usually, price is 7-10 dollars for card like this. so, i guess that it can probably store only 1gb of data, and that rest are bad sectors. however, i would still like to fix it, if it is possible. so, i am looking for some special advanced app which can find and mark all bad sectors on this sd card. i do not know why chkdsk app not format app does that, but those are definitely not advanced apps. they have not changed much since ms-dos 1 in 1981 (format at least). so, i would like to test some more advanced new application which can mark bad sectors.

can you tell me, how to find bad sectors and mark them? is there any application for windows which can do that? some more advanced application then format application, since format application does not work. i mean, it formats sd card, but with its original capacity. there are no bad sectors marked.

thanx for anyone who replies.
bye world.