K750i reboots itself PLEASE HELP !!!

Hi guys! I have a problem with K750i. I got this phone from a friend of mine. When I try to put in a SIM the phone boots normally , does all things up to "Searching" ... (network) .. finds the network and connects to it and 10 seconds later gives me a White screen and reboots. it look like a software reboot since it takes less time to boot up again. If I remove the SIM and restart the phone without a SIM inside it give me the message "insert SIM" and does NOT reboot. With the SIM out phone stays on indefinitely. I flashed 2 times with different firmware and upgrade once using SEUS. Still the same. After the phone finds the network I still have 10 sec to browse the phone until it restart itself and I has able to play a mp3, make a call , take a picture..All of this are working properly. Everything seems to be working fine in that 10 sec until reboots after finding network. it seems that phone had the joystick replaced recently. I mention that Joystick is working flawlessly. I have CID 36 red.
DOES ANYONE KNOW WHAT IT COULD BE?

have u used the sony ericsson update service to reflash it
Sony Ericsson - Support - Software - Z555i - Update Service

Yes , I used SE update service from Sony site and I've flashed the latest firmware in.
But the problem didn't correct. I have the same problem . K750i reboots itself after 10 seconds from finding the network. Do you guys have any ideea of what it may be wrong?
please post if someone had the same problem and found the solution.
THANKS

its sounds like a hard were fault ie sim reader or lcd or battry

Tonight I found a new interesting thing about this phone. I put in a SIM from another country I have (T-mobile) and here there is no T-Mobile network and the phone won't reboot anymore. I put an inactive Vodafone SIM in (there are Vodafone carrier here) and the k750i reboots upon finding signal. To me seems that this has to do with the network. The carrier somehow soft resets the phone. Or, the phone doesn't reboot with T-Mobile SIM since there is no T-Mobile network and RF circuitry is OFF while with Vodafone SIM network is present and RF circuitry is ON (and probably faulty) and that resets the phone.
Any ideeas?

try unlocking

Is it an unlocked phone? If so try a different SIM card and see if it reboots with it. Im thinking it has smething to do with the SIM.

The phone is unlocked.

its a hardwere fult with the sim reader and for the phones age u proply could pick up a cheap pcb will be cheaper than have it fixed

The phone is unlocked. The only SIM I found that the phone will NOT reboot itself with, is a T-Mobile SIM. But here where I live there is no T-mobile carrier. So I'm just assuming that the phone tries to connect to a T-Mobile network according to SIM and since is not finding it gives up and shuts off the radio transmitter. It is very interesting that at all times I have 5 bars of signal on the screen (but I have no idea of what carrier's signal). On the screen anyways it shows INACTIVE SIM and the phone never reboots. I tried switching off the phone manually from power button and it switches off BUT it won't stay off.. in a matter of seconds reboots (switches back on by itself). Have any of you guys encounter this problem??
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When I put in a Vodafone SIM the phone searches for network, finds Vodafone carrier, connects to it, and after 10 sec reboots. Is the network rebooting my phone for some reason? or rejecting the phone? Or I have a faulty radio transmitter module and is drawing to much current and the phone take the decision to shut off.
In the 10 second window of time before reboot I was able to receive a phone call and hear the couterpart saying "Hello" so I know for sure Radio transmitter is working (but I don't know if it draws to much of current).
Any new ideas?

NEW INPUT: the phone will never stay OFF when I shut it off manualy from power button no matter if it has a SIM inserted or not. I removed the battery and then reinserted the battery and this way the phone stays off. Is this pointing to a problem on the PCB or is a common software problem?

the files u flashed it with were did u get them from

For the first 2 flashing jobs I got them from TOPSONY, downloads tab, and the latest flash I did on the phone I used SE upgrade service and I flashed in the latest firmware for K750i.

the next test I'll do is to take the phone in an area with no signal. There I can test of the network reboots my phone. And I'll probably decide if it is a HW problem like FLASH IC or processor or Radio AMP problem.

its hardware problem.. change power amplifier...

A bad Power amp can make my phone not to stay off when I turn it off manually?

Check your sim card. I think that your sim card is error. You should contact supply service

What do you mean by "check your SIM card"? I tried hundreds of times to remove and reseat a handful of diferent SIM cards. All the same. If I don't insert any SIM the phone won't reboot but instead asks for a SIM. It is strange because it started to reboot even with the T-Mobile SIM that it used not to reboot but now started to reboot with that SIM too. I took the phone in an area with no GSM signal and phone still reboots. It is wierd. I'm thinking to reflash the phone with the oldest firmware.. see what happens. Any idea is welcomed.

PROBLEM FIXED. Finally I got to the bottom of this.. (or that I think). I reflashed (again ) the phone with the oldest firmware available on TOPSONY.com which is R1AA008 and the phone won't reboot any more. So it was not a SIM problem or a hardware problem. It is weird anyway. I've noticed another problem though, I have only 3 bars of signals compared with the other 2 k750i's that I own on the same network which have 5 bars. It still may be a power amplifier problem...


UPDATE: After 6 months of heavy use of the SE K750i with the reboot problem it still works strong . No problem since I reflashed with the oldest firmware (which is RAA008). There was no hardware problem. I still can't figure why the phone reboots with all other firmwares. I'm afraid to reflash with a newer FW because I think I will end up with the reboot problem again.
Weird isn't it?
I have only one explanation: the size of FW RAA008 is smaller than all other newer firmwares. I might have a phone with some damaged clusters of internal memory. A large firmware will try to use this part of memory which is damaged while a smaller FW doesn't need to. With a larger FW size the phone will try to access this damaged areas, was unsuccessful and was forced to reboot.
Any ideas?

format memory card or run a scan disk, it will solve your problems, i had the same problem with my K810 from the time when bought and it did solve

I don't have any memory cards in MS slot. Th phone used to reboot even when the slot card was empty.

check for continuous short in ON/OFF button...

Hope this helps...

The problem was fixed by firmware rewrite with the oldest firmware for K750i. I thing I tried 8 different firmware until I got to the bottom of this. I don't know why using that firmware the phone is not rebooting anymore. It has been 1 year since then and the phone is still working good. THANKS guys for trying to help. I appreciate it.