US ROMs on 900/1800 phones

[Peter Poelman]

There has long been talk of it being a general bad idea to install US ROMs on 900/1800 phones. The US T-Mobile ROMs for the longest time have had the RSUpgrade package included in the RUU ROM upgrade, so once you were done flashing your device, the thing would all of a sudden start doing a Radio Upgrade on its own.

I installed the US Siemens/AT&T ROM after concluding it did not have a RSU in it. It worked fine, and came with a new tab in the phone settings called 'Band'. It allowed selection between '900' and '1900', and neither was selected.

So I checked '1900' and figured I could always get back. It said it needed to reset, and I let it.

'No signal'. Makes sense, so I went to the control panel, and set it to '900' and reset again. Still 'No Signal'. Uh oh.... Cold boot, still 'No Signal. Back to Special Edition 1.0 ROM, still 'No Signal'. Upgraded the RSU, which was at 4.16 for this unit, to 4.20. Still 'No signal', no matter how often I cold-boot or whatever. Duh, duh, triple duh!

Guess this is all part of the game... You win some, you lose some...


We're working to get this phone back to life. But let's say there continues to be a stern warning on installing US ROMs on 900/1800 devices. The other way round has never been a problem.

[vpreHoose]

You *should* be able to get it working again be following these steps.

Set the band to 900. Enter Bootloader. Press the Callender button. Scroll down to GSM 900 and press the Action button.

Your device should now work on 900.

[Peter Poelman]

Funny: this occured to me, and I performed the steps necessary, at the same time you must have posted this.

Yes, ofcourse it does work again. So there's three possible positions for the phone to be in: 900, 1900 and 900/1800. Now all we need is the corresponding AT-commands (if that's how they do it), so we can create our own little tool to do band-switching.

So the AT&T ROM can be installed without danger, provided you know how to get back to 900/1800 once if you happens to select one of the radio-buttons in 'band'.

Joy!

[itsme]

If you connect a serial line to your xda while changing mode,
you can see the at commands sent.
900 "AT%CHG900"
1900 "AT%CHG1900"
900/1800 "AT%CHGDUAL"
rfcal "AT%RFCAL"
normal "AT%NORMAL"

[vpreHoose]

Cool, what command did you type to get a list of supported AT commands?

[itsme]

it starts with 'idag.exe bootloader.bin' followed by hours/days of staring at the disassembly