HP-15C LE bricked?

[Hans Brueggemann]

while experimenting with flashing a different firmware on an early HP-15 LE (serno. 003xx), i managed to make it totally unresponsive. the display went out after starting the erase sequence, which i expected. however, i can't see any response from the DBGTX pin when trying to send the firmware via the UART, and mysamba consequently says that it can't connect to the calculator.
i did a reset at some point and had to disconnect the power supply from the calculator, but of course, the erase worked "successfully" and the calculator is brain dead now. i'm not too desperate to get it fixed, but would be willing to change the processor as a last resort. any chance to revive it at this point before going surgical?