For the purpose of debugging of secure provisioning I need to have a SPA508G with the "factory default" firmware, e.g. 7.4.3. So I got the one (with current 7.5.6 firmware) and downgraded it.
The downgrade itself has been successful, but the phone don't start now - dark display, ni LED lighting, even in the case the LAN cable is not connected.
I assume that 7.4.3 firmware is incompatible with either saved configuration or saved dictionary. So bootloader verify that there is valid firmware image, start it, but such image choke on configuration.
Well. Now I need either delete saved configuration or re-upgrade the phone to a new firmware.
But bootloader detected valid firmware, no S.O.S. Recovery mode is available. I can't upgrade the phone using such upgrade mode.
As phone is not starting, it's no way to upgrade it in standard mode nor reset it to factory default.
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