Is my Quark 125B dead

[BrianG]

0.5v and 0.7v?? Is that the throttle signal cable? If so, that's about right. The signal is a PWM ~50Hz with 1-2ms pulses. So, the duty cycle ranges from about 5-10%. Assuming the voltage rail is 5v, those readings are about right (but depends on the meter's capabilities). You really need an oscilloscope to read the signal right.

Are you running an external BEC or receiver pack? And if so, do you have the ESC BEC disabled (remove red wire from the throttle cable)?

Did the ESC just start doing this after several cycles of normal running, or has this been happening ever since you installed it?