Too many doubts in Nokia models

Hello Friends

I got series of questions or doubts to be cleared. Hope that u people help me out.

I got 4 nokia mobile phone models. 5110, 6110, 6150 and 3310. I have succesfully upgraded my 3310 to 3315 with all latest features. Where as when i try to upgrade software version of my other 3 models it always shows Contact Service. The reason for showing contact service problem again and again could be that i may have wrong flash file upgraded to the phone. After flashing these flash files on the phone i check with the software b-phreak eeprom tools - under Test, and i get this result - PPM Checksum is bad. Phone must be repaired. Other link like Update FAID and Set default SP Locks works perfectly, whereas when i click on Repair IMIE - i get the error Phone not connected, please switch on/off the phone and then try.

I also tried solving this problem through Knok and Jordik software, but no result, still i get Contact Service :(

So, now i want to ask u people how to solve this problem ? also, which is the best site to download original mcu+ppm flash files of various mobile phone models like 5110, 6110, 6150 and others ?

Hope you experts can solve my problem and sorry for this lenghty message :)

use chkfixer with the flash file b4 flashing to the phone

Use search engines such as google, etc... to search for fresh flash files.