replace modem.img to test other basebands for MT6589

[g3kamdbs]

I recently bough a MT6589 samsung clone (brand unknown) with flaky 3g data and call issue. Everything works fine in GSM (Edge) mode but not in WCDMA. in WCDMA I can get data only with full signal and the letter above the bar shows H+.

I checked my baseband version to be MOLY.WR8.W1248.MD.WG.MP.V6, 2013/02/20

I have been trying to extract different modem.img files from different ROMS with similar MT6589 chipset. I just renamed the existing modem.img from /system/etc/firmware and replace it with the extracted file also set the correct permission. All of the modem.img(s) seem to be incompatible with my phone, there is no signal at all even the one that shows the same version MP.V6 albeit different compile date.

Are there any extra steps or files that are needed after replacing a baseband/modem file? Do I need to wipe cache etc?

Any help would be appreciated as I am quite a newbie with this android hacking process!