# MCU Boot Loader Troubleshooting

When MCU firmware load is interrupted, or the power-on firmware checksum test fails, the K3 enters its bootstrap loader. You can also force the K3 to enter its bootstrap loader by turning the K3 on with a 10-second press and hold of the front panel POWER button. The MCU boot loader displays MCU LD on the K3 front panel display. The display may not be backlit.

To load K3 firmware, follow these steps in sequence:

- Turn your K3 off by switching off or unplugging its power supply. The K3's microcontroller may continue to run at very low voltage, and it must start from a power-on reset. Disconnect any other connectors that have any possibility of providing power to the K3. A very small leakage current from another device might be enough to keep the MCU from completely resetting. Wait 30-60 seconds before turning power back on.
- If you have a P3 panadapter, disconnect its power connector so that the P3 does not turn on, even for a moment, when you subsequently apply K3 power. Current P3 firmware sends commands that disturb the K3 MCU boot loader. A future P3 firmware revision should remove this constraint, but for now, unplug the P3 power if you find yourself in this situation.
- If the K3 Utility is running, select its Port tab, then close the K3 Utility, by clicking Exit or the red X at the top right of the main window. The Port tab provides the clearest indication of a successful connection when the K3 Utility is subsequently started.
- If you are using a software sharing program such as N8LP's LP-Bridge or microHAM's Router between your personal computer and your K3's RS-232 port, change the cabling so that the PC is connected directly to the K3 without an intervening software "forwarder". These programs send K3 Programmer's Reference commands, and a K3 in its bootstrap loader isn't able to process those commands. Some commands may put the K3 bootstrap loader into an unresponsive state.
- Restart (reboot) the personal computer that will run the K3 Utility. This isn't often necessary, but occasionally a serial port or USB device driver doesn't properly close. Rebooting reinitializes the device and its driver.
- Connect your K3 to its power supply, then press and hold the K3 front-panel POWER button for 10 seconds, until you see MCU LD on the K3 front panel display (without backlighting). The red Tx light should be blinking. Release the POWER button.
- Start the K3 Utility (not the KX3 Utility) and navigate to its Port tab. The K3 Utility should discover the K3 at 38,400 bit/s. If the Port tab has been selected, you should see a dialog that looks something like this:
  If you don't see this dialog, try clicking the Test Communications button. The K3 Utility cannot load firmware if it does not receive responses. Information in USB to Serial Adapter Troubleshooting may help to resolve this issue. The problem might be serial port cabling, an incorrect COM port choice, a problem with the Personal Computer, or the K3's internal KIO3 Interface. Incorrect COM port choice is a common problem here. Sometimes USB to Serial Adapter device drivers change the COM port number unexpectedly. Some devices, such as internal modems, may respond similarly to a K3 in its boot loader.
- When you see this dialog, press its OK button to continue.
- Firmware load can take quite a long time if the View Menu Trace menu item is checked. Uncheck Trace unless you require this diagnostic information.
- Select the Firmware tab, and click Send All New Firmware to K3. If the send buttons are disabled, view Troubleshooting: Send Buttons Disabled.
- The K3 Utility should send MCU firmware to your K3, followed by any other "new" firmware required.