We are MT7628N-A for a project .and the device is booting fine …we are using bus blaster for programming and when we disconnect the USB to TTL converter (UART2) from the device the device is getting stuck and won’t boot again. even if we remove the power also its not working. It will work again work only after connecting the bus blaster.
Hi there and Welcome Here,
So looks to me Like the One of the Strapping pins is not correct. Can you show a picture of the setup and which pins are connected to the Buss Balster /Buss Pirate. The default power up mode makes all IO inputs too, also How which power connection you have. The device has avery specific reset pulse Power up reset requirements.
HTH
GL 
PJ 
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