KEEP THIS PAGE BEFORE YOU UPDATE
A way
back.
Recovery depends on what still responds. The normal MIDI update loader and the chip's UBOOT mode are different things.
1 / The FM-1 still starts
Open the installer, detect the device and back up Bunker music while stopped. Choose Original V15 to return to the manufacturer’s firmware. Older alternatives remain under “Other firmware / archive” in the installer. For V15, download the manufacturer's unchanged FM-1.fwsc and select it locally. Its SHA-256 must match the known package. Install and wait for the final identity check.
Other firmwares do not automatically understand Bunker projects. Restore Bunker first if you later want to restore a Bunker music backup.
2 / An update was interrupted
Keep the device powered. Save the installer log. Close other MIDI programs, reconnect in the installer and choose the same target package. If ota-FM-1 answers, the installer restarts the writing phase from the beginning. It does not resume at the last byte.
Do not repeatedly unplug or reboot while writes may be in progress. The browser only reports success after a responding application returns the expected firmware identity.
3 / The application hangs
The inherited watchdog can restart a stalled application after approximately eight seconds. Two failed starts within the initial startup window can enter UBOOT, the chip update mode. This is not a normal MIDI safe mode.
Holding both OCT− and OCT+ for five seconds while the application is running also enters UBOOT. Do this only when following a chip-recovery procedure. Holding the same keys at power-on enters panel calibration instead.
4 / No compatible MIDI device answers
The browser installer cannot reach every failed application or chip mode. Check the data cable, power and USB port; record the screen state and save any available log. Use the manufacturer's downloads and M-UPGRADE tools or the community's FM-1 transporter documentation for the mode actually detected.
A chip-mode recovery may need separate tools and cannot be promised through Chrome. Do not erase flash sectors, write a raw .bin, or follow a procedure for an unconfirmed board. The normal tested loader preserves the protected boot header and calibration region.
What is protected — and what is not
Bunker keeps the existing eight-voice budget, overload fade and watchdog. There is no hidden remote-access backdoor and no replacement bootloader. These measures limit software overload and help recover from hangs; they do not make power loss during flashing harmless.
On 17 October 2026, the owner confirmed the complete original → Bunker → original update cycle, with working audio and controls. This normal-update test did not test interrupted power. Do not provoke a power failure as a test.