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I have sony xperia z c6603 kddi japan with no signal problem after following this tutorial: see post "

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I hope I can fix 4g network after following these tutorial. But after flash "C6603_10.5.1.A.0.292_baseband_v3.ftf" file, there is no signal at all. Anyone can help my problem? unfortunately, I did not back up TA file before, just dump TA file.

What you did to your phone that phone lost signal? First at all - flash generic Sony au-kddi firmware for that phone model. All parts in order: 1. appsw, 2. fsp. 3. elabel.

Japanese 4g networks are very specific and i don't recommend using their phones as a 4G device outside Japan even if you are lucky and your phone is unlocked. Most likely it's not unlocked. You can use your phone as a gsm device + other smartphone functions should work normally. If you really need LTE (4G) you can buy working unlocked C6603 main board (or phone with broken lcd for example) and swap it.

Thanks for your suggestion. but, I'm so sorry, could you please give me the download link for japanese generic firmware. I can't get the complete parts as you mentions above. May be I'll try both NTT Docomo & KDDI generic firmware. 

I'm sorry, find firmware by yourself. I don't give firmware links to anybody. And don't flash NTT DoCoMo firmware to au-KDDi phones - most likely they are completely different phones.