AIM I-Probe 520 DC offset failed

[icefire]

I have a problem with my iProbe 520.
The DC offset suddenly become zero when i was measuring DC current!
The device now always run on AC mode even when the AC/DC switch is switched to DC.
The calibrator works in AC mode, i can measure the calibrator square waveform.
If i rotate the Trace Position knob, the DC offset move a little bit. But shortly afterward, it return to zero, just like it is running in AC mode.

Anyone have the same issue happened?
I just bought the device on Oct, 2012, just one and a half year. And i pretty sure i have turned on the probe less than 100 hours. Didn't expect the probe is so fragile for a made in England product.